This work is conducted in the framework of the H2020 project DownToTen. This project has received funding from the European Union&#8217;s Horizon 2020 research and innovation programme under grant agreement Nr. 724085.

<ol>
	<li>Dunne, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GRPE+Particulate+Measurement+Programme+(PMP).">GRPE Particulate Measurement Programme (PMP).</a> 7th ETH-Conference on Combustion Generated Nanoparticles. , (2003).</li><li>Sydbom, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Health+effects+of+diesel+exhaust+emissions.">Health effects of diesel exhaust emissions.</a> European Respiratory Journal. 17 (4), 733-746 (2001).</li><li>Vehicle Regulations - Transport. UNECE Available from: <a target="_blank" href="https://www.unece.org/trans/main/welcwp29.html">https://www.unece.org/trans/main/welcwp29.html</a> (2020)</li><li>Andersson, J., Wedekind, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> DETR / SMMT / CONCAWE Particulate Research Programme 1998-2001 SUMMARY REPORT. , (2001).</li><li>Samaras, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Publication+data+form+1.+Framework+Programme+European+Commission-DG+TrEn.">Publication data form 1. Framework Programme European Commission-DG TrEn.</a> 5 th Framework Programme Competitive and Sustainable Growth Sustainable Mobility and Intermodality 2. Contract No. , (2005).</li><li>R&#246;nkk&#246;, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+gaseous+sulphuric+acid+on+diesel+exhaust+nanoparticle+formation+and+characteristics.">Effects of gaseous sulphuric acid on diesel exhaust nanoparticle formation and characteristics.</a> Environmental Science and Technology. 47 (20), 11882-11889 (2013).</li><li>Liati, A., Dimopoulos Eggenschwiler, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+particulate+matter+deposited+in+diesel+particulate+filters:+Visual+and+analytical+approach+in+macro-,+micro-+and+nano-scales.">Characterization of particulate matter deposited in diesel particulate filters: Visual and analytical approach in macro-, micro- and nano-scales.</a> Combustion and Flame. 157 (9), 1658-1670 (2010).</li><li>Liati, A., Schreiber, D., Arroyo Rojas Dasilva, Y., Dimopoulos Eggenschwiler, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafine+particle+emissions+from+modern+Gasoline+and+Diesel+vehicles:+An+electron+microscopic+perspective.">Ultrafine particle emissions from modern Gasoline and Diesel vehicles: An electron microscopic perspective.</a> Environmental Pollution. 239, 661-669 (2018).</li><li>Kittelson, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+Measurements+of+Nanoparticle+Emissions+from+Engines.">Recent Measurements of Nanoparticle Emissions from Engines.</a> Current Research on Diesel Exhaust Particles Japan Association of Aerosol Science and Technology. , 5 (2001).</li><li>Bruno, T. J., Ott, L. S., Smith, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Composition-Explicit+Distillation+Curves+of+Waste+Lubricant+Oils+and+Resourced+Crude+Oil:+A+Diagnostic+for+Re-Refining+and+Evaluation.">Composition-Explicit Distillation Curves of Waste Lubricant Oils and Resourced Crude Oil: A Diagnostic for Re-Refining and Evaluation.</a> American Journal of Environmental Sciences. 6 (6), 523-534 (2010).</li><li>Giechaskiel, B., Vanhanen, J., V&#228;kev&#228;, M., Martini, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+of+vehicle+exhaust+sub-23+nm+particle+emissions.">Investigation of vehicle exhaust sub-23 nm particle emissions.</a> Aerosol Science and Technology. 51 (5), 626-641 (2017).</li><li>. Call: H2020-GV-2016-2017: DownToTen. 48th PMP Update Available from: <a target="_blank" href="https://wiki.unece.org/download/attachments/73924923/PMP-48-10/DTT_Update_Nov_2018.pdf">https://wiki.unece.org/download/attachments/73924923/PMP-48-10/DTT_Update_Nov_2018.pdf</a> (2018)</li><li>. PMP 50th Session - Transport - Vehicle Regulations - UNECE Wiki Available from: <a target="_blank" href="https://wiki.unece.org/display/trans/PMP+50th+Session">https://wiki.unece.org/display/trans/PMP+50th+Session</a> (2019)</li><li>PEMS accuracies under harsh environmental conditions. 23rd Transport and Air Pollution Conference, Thessaloniki 2019 Available from: <a target="_blank" href="https://www.tapconference.org/assets/files/previous-confereces/proceedings/2019_Proceedings.zip">https://www.tapconference.org/assets/files/previous-confereces/proceedings/2019_Proceedings.zip</a> (2019)</li><li>Karjalainen, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-resolved+characterization+of+primary+particle+emissions+and+secondary+particle+formation+from+a+modern+gasoline+passenger+car.">Time-resolved characterization of primary particle emissions and secondary particle formation from a modern gasoline passenger car.</a> Atmospheric Chemistry and Physics. 16 (13), 8559-8570 (2016).</li><li>Mikkanen, P., Moisio, M., Keskinen, J., Ristim&#228;ki, J., Marjam&#228;ki, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sampling+method+for+particle+measurements+of+vehicle+exhaust.">Sampling method for particle measurements of vehicle exhaust.</a> SAE Mobilus. , 219 (2001).</li><li>Giechaskiel, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review+of+motor+vehicle+particulate+emissions+sampling+and+measurement:+From+smoke+and+filter+mass+to+particle+number.">Review of motor vehicle particulate emissions sampling and measurement: From smoke and filter mass to particle number.</a> Journal of Aerosol Science. 67, 48-86 (2014).</li><li>EC Commission Regulation (EU) 2017/1154. Official Journal of the European Union Available from: <a target="_blank" href="https://eur-lex.europa.eu/eli/reg/2017/1154/oj">https://eur-lex.europa.eu/eli/reg/2017/1154/oj</a> (2017)</li><li>Mamakos, A., Khalek, I., Giannelli, R., Spears, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+combustion+aerosol+produced+by+a+mini-CAST+and+treated+in+a+catalytic+stripper.">Characterization of combustion aerosol produced by a mini-CAST and treated in a catalytic stripper.</a> Aerosol Science and Technology. 47 (8), 927-936 (2013).</li><li>Jing, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standard+Combustion+Aerosol+Generator+(SCAG)+for+Calibration+Purposes.">Standard Combustion Aerosol Generator (SCAG) for Calibration Purposes.</a> Atmospheric Environment. 27 (8), 1271-1275 (1999).</li><li>Moore, R. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mapping+the+operation+of+the+miniature+combustion+aerosol+standard+(Mini-CAST)+soot+generator.">Mapping the operation of the miniature combustion aerosol standard (Mini-CAST) soot generator.</a> Aerosol Science and Technology. 48 (5), 467-479 (2014).</li><li>Giechaskiel, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Implementation+of+portable+emissions+measurement+systems+(PEMS)+for+the+real-driving+emissions+(RDE)+regulation+in+Europe.">Implementation of portable emissions measurement systems (PEMS) for the real-driving emissions (RDE) regulation in Europe.</a> Journal of Visualized Experiments. (118), e54753 (2016).</li><li>EC Commission Regulation (EU) 2017/1151. Official Journal of the European Union Available from: <a target="_blank" href="https://eur-lex.europa.eu/eli/reg/2017/1151/oj">https://eur-lex.europa.eu/eli/reg/2017/1151/oj</a> (2017)</li><li>EC REGULATION (EC) No 715/2007 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL. Official journal of the European Union Available from: <a target="_blank" href="https://eur-lex.europa.eu/Legal-content/EN/ALL/?uri=CELEX:32007R0715">https://eur-lex.europa.eu/Legal-content/EN/ALL/?uri=CELEX:32007R0715</a> (2007)</li><li>EC DIRECTIVE 2007/46/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL. Official journal of the European Union Available from: <a target="_blank" href="https://eur-lex.europa.eu/Legal-content/EN/ALL/?uri=CELEX:32007L0046">https://eur-lex.europa.eu/Legal-content/EN/ALL/?uri=CELEX:32007L0046</a> (2007)</li><li>EC Commission Regulation 2790/99. Official Journal of the European Communities Available from: <a target="_blank" href="https://eur-lex.europa.eu/Legal-content/EN/TXT/?uri=CELEX:3A31999R2790">https://eur-lex.europa.eu/Legal-content/EN/TXT/?uri=CELEX:3A31999R2790</a> (1999)</li><li>Hinds, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Aerosol technology: properties, behavior, and measurement of airborne particles. , (2012).</li><li>Badshah, H., Kittelson, D., Northrop, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Particle+Emissions+from+Light-Duty+Vehicles+during+Cold-Cold+Start.">Particle Emissions from Light-Duty Vehicles during Cold-Cold Start.</a> SAE International Journal of Engines. 9 (3), 1775-1785 (2016).</li><li>First results of vehicle technology effects on sub-23nm exhaust particle number emissions using the DownTo10 sampling and measurement system. 22nd ETH-Conference on Combustion Generated Nanoparticles Available from: <a target="_blank" href="https://www.nanoparticles.ch/archive/2018_Andersson_PR.pdf">https://www.nanoparticles.ch/archive/2018_Andersson_PR.pdf</a> (2018)</li><li>Giechaskiel, B., Manfredi, U., Martini, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engine+exhaust+solid+sub-23+nm+particles:+I.+Literature+survey.">Engine exhaust solid sub-23 nm particles: I. Literature survey.</a> SAE International Journal of Fuels and Lubricants. 7 (2834), 950-964 (2014).</li><li>Including cold-start emissions in the Real-Driving Emissions (RDE) test procedure. Publications Office of the European Union Available from: <a target="_blank" href="https://op.europa.eu/en/publication-detail/-/publication/66874f0c-fd85-11e6-8a35-01aa75ed71a1/language-en/format-PDF/source-120155396">https://op.europa.eu/en/publication-detail/-/publication/66874f0c-fd85-11e6-8a35-01aa75ed71a1/language-en/format-PDF/source-120155396</a> (2017)</li><li>Mathissen, M., Scheer, V., Vogt, R., Benter, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+on+the+potential+generation+of+ultrafine+particles+from+the+tire-road+interface.">Investigation on the potential generation of ultrafine particles from the tire-road interface.</a> Atmospheric Environment. 45 (34), 6172-6179 (2011).</li><li>Grigoratos, T., Martini, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brake+wear+particle+emissions:+a+review.">Brake wear particle emissions: a review.</a> Environmental Science and Pollution Research. 22 (4), 2491-2504 (2015).</li></ol>

The authors have nothing to disclose.

This work presents the DTT sampling system and its application as a portable emission measurement system. The system was designed and constructed within the EU Horizon 2020 project DTT to enable particle number emission measurements below the current legislative particle size limit of 23 nm. The system&#8217;s versatility enables the assessment of the regulated solid particle number emissions as well as total particle emissions and studies on secondary aerosols. To interpret measurement results accurately, a calibration procedure is necessary with the DTT system. This is to evaluate the relative particle penetration for different particle sizes, to be able to calculate a correction factor that accounts for the particle losses. It is critical to provide sufficient warm up time for the sampling system itself and the rest of the experimental setup to reach thermal equilibrium and achieve accurate calibration measurement results.
The application of the DTT system for the measurement of solid particle number emissions with a lower particle size cutoff of 23 nm (current regulation) and 10 nm (experimental) is described. To be able to assess particle number emissions of a vehicle it is necessary to determine the particle number concentration and the exhaust mass flow rate. The DTT system covers the particle number concentration measurement. The exhaust mass flow is measured using an exhaust flow meter (EFM). It is critical to install the EFM according to the manufacturer&#8217;s instructions. Erroneous measurements of the exhaust flow rate directly affect the deduced emission rates. When processing the measured data, it is important to perform an accurate time alignment of the particle concentration data and the exhaust flow data. This is necessary because the emission rate is the exhaust flow rate multiplied by the particle number concentration. If the two signals are not aligned correctly, the emissions over the whole drive can significantly deviate from the real emissions.
The DTT system is not a commercial device but a versatile research tool. It is used to investigate unregulated vehicle emissions as opposed to performing certification measurements validating compliance with current regulations. The high versatility comes at the cost of increased energy and dilution air consumption. When using the system for mobile measurements, the weight added to the vehicle due to the battery (30 kg) and gas bottle (20 kg) to cover the energy and air consumption of the system must be kept in mind. The total weight added to the car when measuring the PN emissions with the DTT system is approximately 80 kg, which is comparable to another person being transported in the vehicle. The added weight can lead to slightly increased emissions, especially if the drive includes a great deal of acceleration and/or hills.
The DTT system can be used to investigate the unregulated &#60;23 nm particle number exhaust emissions. Both solid and total particle number emissions can be measured. Furthermore, it can be a useful tool to study the complex field of secondary aerosol formation. Another possible application of the system is the measurement of automotive brake wear particles. A significant fraction of the particles emitted during braking events can be smaller than 30 nm34. With a d50 of approximately 11 nm, the DTT system is suitable for studying these emissions. Although it is known that non-exhaust emissions contribute almost equally to traffic-related PM10 emissions35, non-exhaust particle emissions are still unregulated. This is due to the complex and seldom reproducible process of particle generation, making it very difficult to set regulatory actions. Furthermore, the chemical composition and the related toxicity of organic brake wear particles is still widely unknown35.
The DTT system is a useful tool to improve our understanding of both exhaust and non-exhaust traffic-related particle emissions.

The Particle Measurement Programme (PMP) was founded by the UK Government for the &#8220;development of type approval test protocols for assessing vehicles fitted with advanced particulate reduction technology that would complement or replace current legislative measurement procedures&#8221;1. The PMP is the world&#8217;s first particle number-based emissions regulation, targeted specifically at carbonaceous particles &#8805;23 nm. Recent measurements indicate that it may be necessary to include smaller particles.
Negative health impacts of diesel soot are well understood2, and therefore, the &#8216;precautionary principle&#8217; was invoked on the basis that the elimination of carbon particles from diesel exhaust, via the mandatory use of diesel particulate filters (DPFs), was imperative on health grounds. However, because in European legislation a limit value must force adoption of emissions control technologies, this could not be achieved without an appropriate measurement method. With strong political backing across Europe, the UK Government led the conception of the PMP to improve particulate measurements. The PMP, under the auspices of the United Nations Economic Commission for Europe (UN-ECE)3, included the expertise of others from around the globe. Two particle research projects were completed in 2001. One of them (Particulate Research4) was carried out by the UK Government Department of the Environment, Transport and the Regions (DETR), in partnership with the Society of Motor Manufacturers and Traders (SMMT) and the Oil Companies European Organisation for Environment, Health and Safety (CONCAWE). The other one (PARTICULATES5) was funded by the European Union&#39;s 5th Framework and was carried out by 14 different European partners. The results of both projects indicated that particle number-based procedures were promising, but that challenges for repeatable and reproducible measurements remained.
In 2007 the final report of the PMP Light-duty Inter-laboratory Correlation Exercise was published6, including some improvements on the filter-based mass measurement method, primarily demonstrating the feasibility of a number count-based method for regulatory purposes based upon a defined particle size range and particle volatility. Both methods were implemented based upon sampling from the existing constant volume sampler (CVS) dilution tunnel approach originally developed for particulate matter mass and bagged dilute gaseous emissions measurements.
Within the number count-based method, a lower particle size limit of ~20 nm was selected. The primary objective of the project was to ensure particles of this size and above were controlled by legislation. It is now known that the primary particle size in engine exhaust can be &#60;20 nm7,8,9. For practical reasons, a particle counter with a 50% counting efficiency (d50) at 23 nm was selected, and this size became the accepted lower size threshold. It was recognized that due to the high sensitivity to properties such as dilution, air temperature, humidity, and ratio10, volatile particle size distribution and integrated number measurements could be repeatable in one CVS-equipped facility with one vehicle, but much less so from facility to facility. Thus, for rigorous regulations, it was necessary to focus purely on nonvolatile particles, with the measurement approach effectively defining the regulatory particle boundary conditions on size and volatility. European diesel fuel has back-end volatility such that only a few percent boils at temperatures above 350 &#176;C, and early work within the PMP indicated that short residence times at this temperature were suitable for the complete evaporation of tetracontane, a linear hydrocarbon containing 40 carbon atoms with volatility towards the end boiling point of engine lubricant11. Consequently, a temperature of 350 &#176;C has become the de facto reference point for regulatory &#62;23 nm particle volatility.
The PMP measurement system specification comprises components for sampling, sample conditioning, and measurement, summarized in Table 1.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Stage</td>
			<td>Identity</td>
			<td>Purpose</td>
		</tr>
		<tr>
			<td>0</td>
			<td>Sample source</td>
			<td>Origin of sample</td>
		</tr>
		<tr>
			<td>1</td>
			<td>Particle Transport</td>
			<td>Conduct sample from origin to measurement system</td>
		</tr>
		<tr>
			<td>2</td>
			<td>Volatile Particle Remover</td>
			<td>Eliminate volatiles and define non-volatile particles to be measured</td>
		</tr>
		<tr>
			<td>3</td>
			<td>Particle Number Counter</td>
			<td>Enumerate non-volatile particles and define the lower size limit</td>
		</tr>
	</tbody>
</table>
Table 1: Elements of the PMP Measurement System.
The European PMP PN approach is being implemented and now applies to light-duty diesel (September 2011, EURO 5b) and GDI vehicles (September 2014, EURO 6), and to diesel and gas heavy-duty engines (February 2013, EURO VI).
Recent measurements showed that some light-duty vehicles and, in particular, spark ignition technologies, can emit substantial levels of particles &#60;23 nm12,13,14. This led the European Commission to fund research projects to develop new or extended methods that can be rapidly implemented as a replacement, or addition to, the current &#62;23 nm regulation.
One such project, DownToTen (DTT), aims to preserve the general approach of PMP and extend the measurement range down to a d50 &#8804;10 nm. To this end, the configuration of the DTT measurement system was designed to include the same basic elements described in Table 1, but with the conditioning and measurement steps optimized to enable efficient transport and detection of the &#60;23 nm particles. The DTT system was initially developed for laboratory use but was modified to operate as a portable emissions measurement system (PEMS). For the DTT PN-PEMS system, the components were optimized to reduce weight and power consumption and increase physical robustness without substantially diverging from the original design. For mobile application, the system must be resistant to harsher and erratic temperatures, pressures, and vibration environments likely encountered in light- and heavy-duty PEMS testing. The impact of pressure variations at the inlet of the system was modelled and studied experimentally15. The resistance to vibrations was assessed using a dedicated test bed16. Vibrations and accelerations that occur during typical RDE drives did not impair the measurement results of the condensation particle counters used. The DTT system is also designed for use at low temperatures, where the volatile removal function is inactive, to feed an aging chamber and study secondary organic aerosol formation17.
The thermal conditioning elements of the DTT measurement system that define the regulatory volatility boundary of particles closely parallel the elements of the PMP system in that both systems contain the sequence:
<ol>
	<li>First particle number dilution stage</li>
	<li>HC/volatile elimination stage</li>
	<li>Second particle number dilution stage</li>
</ol>
The primary differences between the DTT and PMP systems are that the DTT system components are selected to:
<ol>
	<li>Maximize transmission of ~10 nm PN from the sample source to the particle counter using low loss dilution and particle transmission approaches</li>
	<li>Comprehensively remove volatiles using oxidative particle elimination rather than merely reducing partial pressures of condensable HC species through evaporation and dilution</li>
	<li>Count particles of ~10&#8211;50 nm with greater efficiency than current PMP systems</li>
</ol>
The objective of this paper is to present the use of the DTT PN-PEMS system for measuring nonvolatile particles &#8805;10 nm from an in-use road vehicle. This includes an introduction to the measurement system and its main components, performing laboratory-based calibration measurements, installing the device for a mobile application, conducting a real driving emission measurement, and processing the collected measurement data.
Instrumentation
The DTT PN-PEMS was designed to provide high particle penetration down to a few nanometers, robust particle number dilution, removal of volatile particles, and prevention of artificial particle formation. The components of the system were selected based on results from laboratory experiments comparing a variety of technologies for dilution and aerosol conditioning. This section provides an overview of the system, its working principle, and the components used. Figure 1 shows a schematic of the system. Figure 2 shows a photo of the system. The DTT system is 60 cm high and has a footprint of 50 cm x 50 cm. The weight of the system is approximately 20 kg. Including the required peripheral elements (i.e., battery and gas bottle) the total weight is approximately 80 kg. The major elements of the system are the two dilution stages (i.e., first hot, second cold), a catalytic stripper, and at least one condensation particle counter (CPC).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61287/61287fig01.jpg" /> 
Figure 1: Schematic drawing of the DTT particle number portable emission measurement system. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61287/61287fig02.jpg" /> 
Figure 2: Top view picture of the DTT sampling system. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Two dilution stages reduce the particle number concentrations to levels measurable by condensation particle counters (&#60;104 #/cm3). Custom-made porous tube diluters are used for both dilution stages. This technology was selected because of its low particle loss18,19. The radial ingress of dilution air convectively keeps particles away from the walls, which reduces particle losses. Furthermore, these diluters can be very small and can withstand temperatures of 400 &#176;C. The porous material used is a sintered hastalloy X tube (GKN Filters Metals GmbH, Radevormwald, Germany). Static mixing elements inside the porous tube provide a well-mixed aerosol directly downstream of the diluter. This allows taking a representative sample of the diluted aerosol for further conditioning or measurement by splitting the aerosol flow directly downstream of the diluter, and allows for a compact sampling system. The primary dilution stage is typically heated to 350 &#176;C, while the second stage is operated at ambient temperature. The dilution factor of the system is approximately 80. The exact value is dependent on the inlet flow and the mass flow management: The flow rates in the sampling system are managed by a system of two mass flow controllers and two mass flow meters. The mass flow controllers control the dilution air flow rates. The mass flow meters monitor the flow rates extracted downstream of dilution stages 1 and 2. The differences between the flows extracted and the flows supplied can be changed. In other words, the net flow added or subtracted in one dilution stage can be defined. The sample flow rate, Qsample, is defined as the sum of all other flow rates: 1) Flow rate drawn by the measurement instruments (Qinst); 2) the dilution air flow rates (Qdil,i); and 3) the excess flow rates Qex,i. For the calculation of the sample flow, the contributions of the flows extracted from the system are positive and the contributions of the flows fed into the system are negative.
<img alt="Equation 1" src="/files/ftp_upload/61287/61287equ01.jpg" />
The total dilution ratio DR is calculated by:
<img alt="Equation 2" src="/files/ftp_upload/61287/61287equ02.jpg" />
A catalytic stripper (CS) is situated between dilution stage 1 and 2 and is operated at 350 &#176;C at a flow rate of 1 liter per minute (L/min). The catalytic stripper provides oxidation of organic compounds and sulphur storage. The removal of these substances ensures the isolation of the solid particle fraction. The undesired formation of volatile and semivolatile particles and growth of subcut size particles is prevented. The catalytic stripper used is commercially available (AVL GmbH). The volatile particle removal efficiency of the CS was verified with polydisperse emery oil particles &#62;50 nm and &#62;1 mg/m3 (3.5&#8211;5.5 mg/m3) showing an efficiency of &#62;99% (actual value 99.9%) as defined by RDE regulations20. This is a more rigorous test than the tetracontane test prescribed in the current PMP protocol.
One or more condensation particle counters are used to measure the particle number concentration downstream of the second dilution stage. A CPC with a d50 of 23 nm enables the measurement of the currently regulated emission of solid particles larger than 23 nm. Additionally, measuring the particle number concentration with one or more CPCs with a lower d50 cut point (e.g., 10 nm, 4 nm) enables the assessment of the currently unregulated solid particle fraction &#60;23 nm down to the d50 cut size of the applied CPC.
The dilution air supply line, the primary porous tube diluter, and the catalytic stripper have independent heating elements containing k-type thermocouples (TC). Independently heating different sections controls the temperature distribution in the system.
In addition to the thermocouples in the heating elements, two thermocouples are placed downstream of dilution stage 1 and 2. These two thermocouples directly measure the aerosol temperature.
Two absolute pressure sensors (NXP MPX5100AP) are used to monitor the pressure at the inlet and the outlet of the sampling system.
For mobile measurements, a Clayton Power LPS 1500 battery pack is used. A 10 L synthetic air bottle supplies the system with dilution air during mobile applications. The sizes of the battery and the gas bottle are chosen so that the system can operate independently for 100 min.
The system is controlled via a NI myRIO running a LabVIEW virtual instrument. The virtual instrument allows for control of the flow rates and heater temperatures. Apart from the controlled parameters, the aerosol temperatures, pressures, and acceleration (via the sensor integrated in myRIO) can be monitored and logged. A myRIO accessory GPS module enables logging of the position data. Figure 3 and Figure 4 show the user interface of the virtual instrument used for controlling the DTT system.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61287/61287fig03.jpg" /> 
Figure 3: DTT virtual instrument dilution stage parameter overview. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61287/61287fig04.jpg" /> 
Figure 4: DTT virtual instrument heater control panel. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Any kind of sampling procedure causes particle losses. To be able to account for these losses, laboratory measurements are performed to determine the particle size dependent particle penetration through the DTT sampling system. In these measurements, the particle concentration of monodisperse aerosol is measured upstream and downstream of the sampling system using two condensation particle counters. Figure 5 shows the experimental setup for the calibration measurements. In this setup, a Jing miniCAST is used as a particle source21,22. Mass flow controllers (MFC) are used to control the gas flows into the burner. A dilution bridge enables the adjustment of the particle number concentration. The dilution bridge is a high-efficiency particulate air (HEPA) filter parallel to a needle valve. Adjusting the position of the needle valve alters the dilution ratio by changing the ratio between the fraction of the aerosol passing through the HEPA filter and the fraction of the aerosol passing through the needle valve. The filtered and the unfiltered aerosols are recombined with a T-piece to form a diluted aerosol. A catalytic stripper is used to remove possibly abundant volatile compounds generated as byproducts of the combustion process. A TSI 3082 electrostatic classifier together with a TSI 3085 differential mobility analyzer (nano DMA) are used for the size selection of particles. Two TSI CPCs 3775 (d50 = 4 nm) are used to measure the particle number concentration upstream and downstream of the DTT sampling system. The counters&#8217; cut point of d50 = 4 nm allows for the penetration determination at particle sizes as low as 10 nm and below.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61287/61287fig05.jpg" /> 
Figure 5: Schematic drawing of the experimental setup used for the calibration of the DTT sampling system. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table>
	<tbody>
		<tr>
			<td>2x Condensation Particle Counter 4 nm</td>
			<td>TSI</td>
			<td>3775</td>
			<td>Particle counter with a cut point of 4 nm</td>
		</tr>
		<tr>
			<td>5x Mass Flow Controllers (MFC)</td>
			<td>V&#246;gtlin</td>
			<td></td>
			<td>Mass flow controllers for controlling the miniCast gas flows</td>
		</tr>
		<tr>
			<td>AVL M.O.V.E. EFM Exhaust Flow Meter</td>
			<td>AVL</td>
			<td></td>
			<td>Device for the measurement of the exhaust flow rate of vehicles</td>
		</tr>
		<tr>
			<td>Catalytic Stripper</td>
			<td>Custom made</td>
			<td></td>
			<td>Device for the removal of volatile compounds in an aerosol by oxidation</td>
		</tr>
		<tr>
			<td>Compressed Air</td>
			<td></td>
			<td></td>
			<td>Oxidation and dilution air supply for miniCast</td>
		</tr>
		<tr>
			<td>Condensation Particle Counter 10 nm</td>
			<td>AVL</td>
			<td></td>
			<td>Particle counter with a cut point of 10 nm</td>
		</tr>
		<tr>
			<td>Condensation Particle Counter 23 nm</td>
			<td>TSI</td>
			<td>3790A</td>
			<td>Particle counter with a cut point of 23 nm</td>
		</tr>
		<tr>
			<td>Differential Mobility Analyzer</td>
			<td>TSI</td>
			<td>3085</td>
			<td>Part of the electrostatic classifier where the particle are separeted by mobility.</td>
		</tr>
		<tr>
			<td>Dilution Bridge</td>
			<td>Custom made</td>
			<td></td>
			<td>Needle valve in parallel to HEPA filters. Used to adjust particle concentrations for calibration purposes</td>
		</tr>
		<tr>
			<td>DownToTen Sampling System</td>
			<td>Custom made</td>
			<td></td>
			<td>Custom made sampling system for the assessment of automotive sub-23 nm particle emissions</td>
		</tr>
		<tr>
			<td>Electrostatic Classifier</td>
			<td>TSI</td>
			<td>3082</td>
			<td>Device for the classifaction of arosol particles by electrical mobility diameter</td>
		</tr>
		<tr>
			<td>Hand held Mass Flow Meter (MFM)</td>
			<td>V&#246;gtlin</td>
			<td></td>
			<td>Device for measuring the inlet flow of measurement instruments</td>
		</tr>
		<tr>
			<td>miniCast Soot Generator</td>
			<td>Jing Ltd</td>
			<td></td>
			<td>Combastion aerosol standard, soot generator</td>
		</tr>
		<tr>
			<td>Mobile Battery LPS 1500</td>
			<td>Clayton Power</td>
			<td></td>
			<td>Battery for power supply of the DTT measurement system</td>
		</tr>
		<tr>
			<td>Nitrogen Gas Bottle</td>
			<td></td>
			<td></td>
			<td>Nitrogen for Mixing gas and quench gas supply of miniCast</td>
		</tr>
		<tr>
			<td>Propane Gas Bottle</td>
			<td></td>
			<td></td>
			<td>Fuel for miniCast</td>
		</tr>
		<tr>
			<td>Soft X-Ray Neutralizer</td>
			<td>TSI</td>
			<td>3088</td>
			<td>Device for the establishmentof the equillibrium charge distribution of aerosol particles</td>
		</tr>
		<tr>
			<td>Synthetic Air Bottle 10 L</td>
			<td></td>
			<td></td>
			<td>Gas Bottle for the dilution air supply</td>
		</tr>
	</tbody>
</table>

measuring sub-23 nanometer real driving particle number emissions using the portable downtoten sampling system

The current particle size threshold of the European Particle Number (PN) emission standards is 23 nm. This threshold could change because future combustion engine vehicle technology may emit large amounts of sub-23 nm particles. The Horizon 2020 funded project DownToTen (DTT) developed a sampling and measurement method to characterize particle emissions in this currently unregulated size range. A PN measurement system was developed based on an extensive review of the literature and laboratory experiments testing a variety of PN measurement and sampling approaches. The measurement system developed is characterized by high particle penetration and versatility, which enables the assessment of primary particles, delayed primary particles, and secondary aerosols, starting from a few nanometers in diameter. This paper provides instruction on how to install and operate this Portable Emission Measurement System (PEMS) for Real Drive Emissions (RDE) measurements and assess particle number emissions below the current legislative limit of 23 nm.

Calibration Data (Particle Penetration):
Figure 11 shows an exemplary plot of the relative particle penetration of the DTT system as a function of the particle mobility diameter. The corresponding data have been measured and evaluated as described in instruction section 1. The plot shows that the deviations between two measurement points at the same mobility diameter were less than 5%. Deviations larger than 10% indicate instabilities in the experimental setup. In this case, the calibration had to be repeated with increased warm up stabilization times. Both the warm up time (typically 30 min) and the stabilization time (typically 30 s) increased by a factor of 1.5.
The particles passing through the DTT system were lost due to diffusion and thermophoresis. Thermophoretic losses were caused by a temperature gradient drawing particles towards the walls of the sampling system. This is a particle size independent effect29; in contrast, diffusion is highly particle size dependent. A concentration gradient caused a net particle flux towards the walls where particles were lost. The diffusivity rising with lower particle size made this the dominant loss mechanism for particles &#8804;10 nm. The lines in Figure 11 indicating thermophoretic, diffusional, and total losses demonstrate the respective particle size dependencies. For the diffusional losses, this function was used to illustrate the approximate particle size dependency:
<img alt="Equation 11" src="/files/ftp_upload/61287/61287equ11.jpg" />
The penetration P depends on a fit parameter a and the diffusion coefficient D:
<img alt="Equation 12" src="/files/ftp_upload/61287/61287equ12.jpg" />
The diffusion coefficient depends on the Boltzmann constant k, the absolute temperature T, the viscosity &#951;, the particle diameter dp, and the Cunningham slip correction factor Cc, which is a function of the mean free path and the particle diameter29.
The data illustrated in Figure 11 resulted in the following mean particle penetration efficiency Pmean:
<img alt="Equation 13" src="/files/ftp_upload/61287/61287equ13.jpg" />
The particle size where the penetration efficiency amounts to 50% is referred to as d50. The d50 describes the penetration cutoff characteristic of a system. For the DTT system the d50 was 11 nm. The d50 is shown in Figure 11.
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/61287/61287fig11.jpg" /> 
Figure 11: Particle penetration as a function of particle mobility diameter. 
Points marked in blue are measurement results. The dashed lines in orange and green indicate the losses associated with thermophoresis and diffusion, respectively. The red line represents the total losses as the sum of diffusional and thermophoretic losses. The dotdashed purple line shows the average particle penetration Pmean as calculated in the calibration measurement instruction section 1. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Solid Particle Number:
Figure 12 shows the particle number emission rate over time for the first ten minutes of an RDE measurement drive. The data from the DTT PEMS using a 10 nm and a 23 nm CPC are shown together with data from a commercially available 23 nm cut point system. The particle emission rates were calculated from the respective particle concentrations multiplied by the exhaust flow rate as described above in the data analysis instruction section 4. The reference instrument (AVL MOVE) relied on a diffusion charger for the particle number concentration measurement. Despite the different sensor principles, the data measured with the DTT PEMS were overall in very good agreement with the data measured by the commercially available PEMS. Sharp downwards pointing spikes in all three signals occurred because the particle measurement devices can report zero particle concentrations temporarily and zeros cannot be displayed in logarithmic plots. The particle emissions measured with the 10 nm CPC were very close to the emissions measured with the 23 nm CPC for the majority of the time period shown in Figure 12. However, right at the beginning between 10 s and 25 s there was an occurrence of significant &#60;23 nm particle emission. The DTT 10 nm signal was significantly higher than the 23 nm signal of the DTT system and the AVL MOVE. In this case, &#62;50% of the total number of particles emitted were between 10 nm and 23 nm. Cold start dynamic processes in non-thermal equilibrium can cause particle size distributions to differ from emissions from a hot vehicle30. The discussion of these complex processes is beyond the scope of this work. Further information on this topic can be found in the literature31,32,33.
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/61287/61287fig12.jpg" /> 
Figure 12: The upper part of the figure shows the particle number emission rate over time for the first 10 mins of an RDE measurement drive. 
Data measured with the DTT PEMS using 10 nm and 23 nm CPC and a commercially available 23 nm cut point system (AVL MOVE) are used as a reference. The lower part of the figure shows the velocity of the vehicle. <a href="https://www.jove.com/files/ftp_upload/61287/61287fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Measuring Sub-23 Nanometer Real Driving Particle Number Emissions Using the Portable DownToTen Sampling System at JoVE.com

Measuring Sub-23 Nanometer Real Driving Particle Number Emissions Using the Portable DownToTen Sampling System

Presented here is the DownToTen (DTT) portable emission measurement system to assess real driving automotive emissions of sub-23 nm particles.

The current particle size threshold of the European Particle Number (PN) emission standards is 23 nm. This threshold could change because future ...

measuring-sub-23-nanometer-real-driving-particle-number-emissions

Research

JoVE Journal

Engineering

5.4K Views.  Graz University of Technology. Presented here is the DownToTen (DTT) portable emission measurement system to assess real driving automotive emissions of sub-23 nm particles.

Video: Measuring Sub-23 Nanometer Real Driving Particle Number Emissions Using the Portable DownToTen Sampling System

Echo Particle Image Velocimetry

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.2 For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.3,4,5,6 In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine7 with a PC running commercial particle image velocimetry (PIV) software8 is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported.
For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/&delta;t. (See 9 for a review of ultrasound imaging.)
For a typical EPIV experiment, the frame rate is between 20-60 fps, depending on flow conditions, and 100-1000 B-mode images of the spatial distribution of the tracer particles in the flow are acquired. Once acquired, the B-mode ultrasound images are transmitted via an ethernet connection to the PC running the PIV commercial software. Using the PIV software, tracer particle displacement fields, D(x,y)[pixels], (where x and y denote horizontal and vertical spatial position in the ultrasound image, respectively) are acquired by applying cross correlation algorithms to successive ultrasound B-mode images.10 The velocity fields, u(x,y)[m/s], are determined from the displacements fields, knowing the time step between image pairs, &Delta;T[s], and the image magnification, M[meter/pixel], i.e., u(x,y) = MD(x,y)/&Delta;T. The time step between images &Delta;T = 1/fps + D(x,y)/B, where B[pixels/s] is the time it takes for the ultrasound probe to sweep across the image width. In the present study, M = 77[&mu;m/pixel], fps = 49.5[1/s], and B = 25,047[pixels/s]. Once acquired, the velocity fields can be analyzed to compute flow quantities of interest.

An echo particle image velocimetry (EPIV) system capable of acquiring two-dimensional fields of velocity in optically opaque fluids or through optically opaque geometries is described, and validation measurements in pipe flow are reported.

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 ...

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model

Analysis of the size distribution of nanocrystals is a critical requirement for the processing and optimization of their size-dependent properties. The common techniques used for the size analysis are transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). These techniques, however, are not suitable for analyzing the nanocrystal size distribution in a fast, non-destructive and a reliable manner at the same time. Our aim in this work is to demonstrate that size distribution of semiconductor nanocrystals that are subject to size-dependent phonon confinement effects, can be quantitatively estimated in a non-destructive, fast and reliable manner using Raman spectroscopy. Moreover, mixed size distributions can be separately probed, and their respective volumetric ratios can be estimated using this technique. In order to analyze the size distribution, we have formulized an analytical expression of one-particle PCM and projected it onto a generic distribution function that will represent the size distribution of analyzed nanocrystal. As a model experiment, we have analyzed the size distribution of free-standing silicon nanocrystals (Si-NCs) with multi-modal size distributions. The estimated size distributions are in excellent agreement with TEM and PL results, revealing the reliability of our model.

We demonstrate how to determine the size distribution of semiconductor nanocrystals in a quantitative manner using Raman spectroscopy employing an analytically defined multi-particle phonon confinement model. Results obtained are in excellent agreement with the other size analysis techniques like transmission electron microscopy and photoluminescence spectroscopy.

Analysis of the size distribution of nanocrystals is a critical requirement for the processing and optimization of their size-dependent properties. The ...

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their behavior for single stages of a process or even an entire process. For the simulation with occurring particle-particle and particle-wall contacts, the value of the coefficient of restitution is required. It can be determined experimentally. The coefficient of restitution depends on several parameters like the impact velocity. Especially for fine particles the impact velocity depends on the air pressure and under atmospheric pressure high impact velocities cannot be reached. For this, a new experimental setup for free-fall tests under vacuum conditions is developed. The coefficient of restitution is determined with the impact and rebound velocity which are detected by a high-speed camera. To not hinder the view, the vacuum chamber is made of glass. Also a new release mechanism to drop one single particle under vacuum conditions is constructed. Due to that, all properties of the particle can be characterized beforehand.

The coefficient of restitution is a parameter that describes the loss of kinetic energy during collision. Here, a free-fall setup under vacuum conditions is developed to be able to determine the coefficient of restitution parameter for particles in micrometer range with high impact velocities.

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their ...

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is &#177; 5 parts in 107. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength.

We describe the generation of far-infrared radiation using an optically pumped molecular laser along with the measurement of their frequencies with heterodyne techniques. The experimental system and techniques are demonstrated using difluoromethane (CH2F2) as the laser medium whose results include three new laser emissions and eight measured laser frequencies.

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and ...

Design and Use of a Full Flow Sampling System (FFS) for the Quantification of Methane Emissions

The use of natural gas continues to grow with increased discovery and production of unconventional shale resources. At the same time, the natural gas industry faces continued scrutiny for methane emissions from across the supply chain, due to methane&#39;s relatively high global warming potential (25-84x that of carbon dioxide, according to the Energy Information Administration). Currently, a variety of techniques of varied uncertainties exists to measure or estimate methane emissions from components or facilities. Currently, only one commercial system is available for quantification of component level emissions and recent reports have highlighted its weaknesses.
In order to improve accuracy and increase measurement flexibility, we have designed, developed, and implemented a novel full flow sampling system (FFS) for quantification of methane emissions and greenhouse gases based on transportation emissions measurement principles. The FFS is a modular system that consists of an explosive-proof blower(s), mass airflow sensor(s) (MAF), thermocouple, sample probe, constant volume sampling pump, laser based greenhouse gas sensor, data acquisition device, and analysis software. Dependent upon the blower and hose configuration employed, the current FFS is able to achieve a flow rate ranging from 40 to 1,500 standard cubic feet per minute (SCFM). Utilization of laser-based sensors mitigates interference from higher hydrocarbons (C2+). Co-measurement of water vapor allows for humidity correction. The system is portable, with multiple configurations for a variety of applications ranging from being carried by a person to being mounted in a hand drawn cart, on-road vehicle bed, or from the bed of utility terrain vehicles (UTVs). The FFS is able to quantify methane emission rates with a relative uncertainty of &#177; 4.4%. The FFS has proven, real world operation for the quantification of methane emissions occurring in conventional and remote facilities.

Design and Use of a Full Flow Sampling System FFS for the Quantification of Methane Emissions

We have designed, developed, and implemented a novel full flow sampling system (FFS) for quantification of methane emissions and greenhouse gases from across the natural gas supply chain.

The use of natural gas continues to grow with increased discovery and production of unconventional shale resources. At the same time, the natural gas ...

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown that when operated in amplitude-modulation (tapping) mode, atomic or molecular-level resolution images can be achieved over a wide range of soft and hard samples in liquid. In these situations, small oscillation amplitudes (SAM-AFM) enhance the resolution by exploiting the solvated liquid at the surface of the sample. Although the technique has been successfully applied across fields as diverse as materials science, biology and biophysics and surface chemistry, obtaining high-resolution images in liquid can still remain challenging for novice users. This is partly due to the large number of variables to control and optimize such as the choice of cantilever, the sample preparation, and the correct manipulation of the imaging parameters. Here, we present a protocol for achieving high-resolution images of hard and soft samples in fluid using SAM-AFM on a commercial instrument. Our goal is to provide a step-by-step practical guide to achieving high-resolution images, including the cleaning and preparation of the apparatus and the sample, the choice of cantilever and optimization of the imaging parameters. For each step, we explain the scientific rationale behind our choices to facilitate the adaptation of the methodology to every user's specific system.

We present a method for achieving sub-nanometer resolution images with amplitude-modulation (tapping mode) atomic force microscopy in liquid. The method is demonstrated on commercial atomic force microscopes. We explain the rationale behind our choices of parameters and suggest strategies for resolution optimization.

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown ...

Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.

We present a parametric driving method to cool an ultracold Fermi gas in a crossed-beam optical dipole trap. This method selectively removes high-energy atoms from the trap by periodically modulating the trap depth with frequencies that are resonant with the anharmonic components of the trapping potential.

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs ...

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Optimized sampling protocols and the development of new wipe materials can be facilitated by standardized measurements of collection efficiency from wipe-sampling. Our approach for sampling trace explosives uses an automated device to control speed, force, and distance during wipe-sampling followed by extraction of collected explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common ...

Simultaneous Measurement of Turbulence and Particle Kinematics Using Flow Imaging Techniques

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine micro-organisms, and/or sediments in the ocean, or fluidized bed reactors and combustion processes in engineered systems. In order to study the effect of turbulence on the kinematics of particles in such flows, simultaneous measurements of both the flow and particle kinematics are required. Non-intrusive, optical flow measurement techniques for measuring turbulence, or for tracking particles, exist but measuring both simultaneously can be challenging due to interference between the techniques. The method presented herein provides a low cost and relatively simple method to make simultaneous measurements of the flow and particle kinematics. A cross section of the flow is measured using a particle image velocimetry (PIV) technique, which provides two components of velocity in the measurement plane. This technique utilizes a pulsed-laser for illumination of the seeded flow field that is imaged by a digital camera. The particle kinematics are simultaneously imaged using a light emitting diode (LED) line light that illuminates a planar cross section of the flow that overlaps with the PIV field-of-view (FOV). The line light is of low enough power that it does not affect the PIV measurements, but powerful enough to illuminate the larger particles of interest imaged using the high-speed camera. High-speed images that contain the laser pulses from the PIV technique are easily filtered by examining the summed intensity level of each high-speed image. By making the frame rate of the high-speed camera incommensurate with that of the PIV camera frame rate, the number of contaminated frames in the high-speed time series can be minimized. The technique is suitable for mean flows that are predominantly two-dimensional, contain particles that are at least 5 times the mean diameter of the PIV seeding tracers, and are low in concentration.

The technique described herein offers a low cost and relatively simple method to simultaneously measure particle kinematics and turbulence in flows with low particle concentrations. The turbulence is measured using particle image velocimetry (PIV), and particle kinematics are calculated from images obtained with a high-speed camera in an overlapping field-of-view.

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine ...

Measurement of Dynamic Force Acted on Water Strider Leg Jumping Upward by the PVDF Film Sensor

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, with its peak locomotion speed reaching 150 cm/s. First of all, we observed the microstructure and hierarchy of water strider legs using the scanning electron microscope. On the basis of the observed morphology of the legs, a theoretical model of the detachment from water surface was established, which explained water striders' capability to slide on water surface effortlessly in terms of energy reduction. Secondly, a dynamic force measurement system was devised using the PVDF film sensor with excellent sensitivity, which could detect the whole interaction process. Subsequently, a single leg in contact with water was pulled upward at different speeds, and the adhesion force was measured at the same time. The results of the departing experiment suggested a deep understanding of the fast jumping of water striders.

The protocol here is dedicated to investigating the free and quick maneuvering of water strider on water surface. The protocol includes observing the microstructure of legs and measuring the adhesion force when departing from water surface at different speeds.

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, ...