This material is based upon work supported by the National Science Foundation Environmental Chemical Sciences Program in the Division of Chemistry under Grant No. 1111418, the Atmospheric-GeoSciences Division of the U.S. National Science Foundation (NSF) under grant number 1524731, as well as Harvard Faculty Publication Award. We acknowledge Mona Shrestha, Adam Bateman, Pengfei Liu, and Mikinori Kuwata for useful discussions and assistance with the experiments.

1. Gas-Phase Injection of the Flow Tube Reactor
<ol>
	<li>Organic Precursor Injection 
	NOTE: All the equipment and software used during the experiment can be found in the&#160;Table of Materials. Depending on the purpose of the experiments, a wide range of volatile organic compounds can be used as the organic precursor for the experiment. &#945;-Pinene is used here as an example for the procedure of injecting the organic precursor into the flow tube reactor.
	<ol>
		<li>Use a micropipette to obtain 1.00 mL of &#945;-pinene. Transfer the liquid to a 50.00 mL volumetric flask.</li>
		<li>Use 2-butanol to fill the volumetric flask to 50.00 mL, thereby diluting the &#945;-pinene by a ratio of 1:50. Shake the volumetric flask to mix the solvent and the solute thoroughly.</li>
		<li>Use a syringe (5.00 mL) to withdraw the &#945;-pinene solution. Rinse the syringe three times with the solution and then fill it with solution.</li>
		<li>Connect the syringe to a sharp needle (25 gauge, 2-inch long). Place the syringe onto a syringe injector. Insert the needle tip into a vaporizer round-bottom flask (25 mL). Pre-heat the vaporizer flask to 135 &#177; 1 &#176;C by heating tape.</li>
		<li>Introduce a gentle flow of 0.5 sLpm purified air to vaporize and carry away &#945;-pinene injected from the syringe. Connect the purified air generator to the same power supply as the heating tape to avoid heating the round bottom flask if the pure air supply is stopped.</li>
		<li>Turn on the syringe injector, and adjust the injection rate to an appropriate value. Calculate the injection rate by applying the gas flow rate, the desired VOC concentration and the syringe size to the Clausius-Clapeyron equation. For instance, for a total flow of 4.5 sLpm, to reach 125 ppb of &#945;-pinene would require an injection rate of 11.7 &#956;L/h of the &#945;-pinene and 2-butanol mixture. Ensure that the volumetric concentration of butanol or &#945;-pinene is less than 1% in the round bottom flask to avoid the organic compounds reach the flammability limit.</li>
	</ol>
	</li>
	<li>Ozone Injection
	<ol>
		<li>Pass a flow of air at 4.00 sLpm through an ozone generator.</li>
		<li>Turn on the ozone generator. Control the ozone concentration to appropriate values by adjusting the length of the glass tube shielding the UV lamp inside the generator. The ozone and VOC ratios can vary across two orders of magnitudes depending on the purpose of the experiment. If VOC is needed to be fully reacted during the experiment, then the ozone concentration should be about 10 times higher than the VOC concentration to ensure ozone is in excess.</li>
		<li>Turn on the ozone concentration monitor and connect the ozone monitor to the computer. Using a terminal reader software to access the ozone monitor readout and save the data obtained from the ozone monitor (Figure 2). Perform the experiments after the ozone concentration stabilizes.</li>
	</ol>
	</li>
</ol>
2. Particle Production of the Flow Tube Reactor
<ol>
	<li>Adjustment of residence time
	<ol>
		<li>Unscrew the cap at the end of the flow tube reactor to adjust the position of the movable sampler tubing inside the flow tube reactor. Change different positions of the movable sampler tubing subsequently to achieve different residence times from 3 s to 38 s10.</li>
		<li>During each experiment, change the position of the movable sampler to adjust the residence time of the particles being produced inside the flow tube reactor.</li>
		<li>Position the movable sampler at the beginning of the flow tube reactor (0.10 m from the gas inlet) to obtain the shortest residence time (3 s). Position the movable sampler at the end of the flow tube reactor (1.30 m from the gas inlet) to obtain the longest residence time (38 s).</li>
	</ol>
	</li>
	<li>Temperature control for particle production
	<ol>
		<li>House the flow tube reactor in a temperature-controlled, double-walled, water-jacketed stainless-steel box. Perform a leak check and a water level check prior to each set of experiments.</li>
		<li>Set the temperature of the thermostat in the water circulator to 20.0 &#176;C. 
		NOTE: Temperature during the course of an experiment varies by no more than 0.1 &#176;C.</li>
		<li>Turn on the temperature recording software in the main computer, and set the data sampling time to 10 s (Figure 3). The temperature sensor is located at the center point of the flow tube. Start logging the temperature measured from the temperature sensor when turning on the&#160;Record&#160;button.</li>
		<li>Record the temperature for 4 to 6 h. Stabilize the temperature before performing the experiment. 
		NOTE: The temperature fluctuation of the flow tube reactor is less than &#177; 0.1 &#176;C during a 24-hour period.</li>
	</ol>
	</li>
	<li>The pressure monitoring system
	<ol>
		<li>Connect a pressure monitor to the flow tube outlet through a &#188; inch connector and the main computer</li>
		<li>Turn on the pressure monitor software (Figure 4), and then click&#160;File&#160;|&#160;New&#160;|&#160;Time/Sample Interval&#160;to set the sampling interval to 10 s.</li>
		<li>Click on&#160;Total Data Points&#160;to set the sampling length to 36,000 points. Click&#160;OK&#160;to record the data. 
		NOTE: The outlet pressure stays within &#177; 0.01 atm during a 24-hour period, suggesting the pressure within the flow tube is stable.</li>
	</ol>
	</li>
</ol>
3. Characterization of Produced Particle Population of the Flow Tube Reactor
<ol>
	<li>Number-diameter distributions
	<ol>
		<li>Connect the outlet of the flow tube reactor to a scanning mobility particle sizer (SMPS) by electrostatic-resistant tubing. Similar instrument can also be used to measure the number-diameter distributions instead of the SMPS. 
		NOTE: The detailed operating procedures or troubleshooting of the SMPS can be found in its manual.</li>
		<li>Start the software that records the number-diameter distribution. Create a new file by clicking on&#160;Create A New File. Set each parameter shown in&#160;Figure 5. Record the number-diameter distributions of the particles exiting the flow tube reactor by clicking on&#160;OK&#160;button.</li>
	</ol>
	</li>
	<li>Relative humidity control
	<ol>
		<li>Connect the two inlets of a water bubbler to two mass flow controllers (MFCs) so as to adjust the humidity of the sheath air in the flow tube. Adjust the flow rate of the two inlets from 0-10 sLpm so as to change the relative humidity of the sheath air from &#60;5% to &#62;95%.</li>
		<li>Connect the outlet of the water bubbler to the sheath air inlet of the permeable membrane tube. Connect the outlet of the flow tube reactor to the main sampling inlet of the same permeable membrane tube.</li>
		<li>Connect a relative humidity (RH) sensor to the outlet of the permeable membrane tube to measure the RH of the sampling air.</li>
		<li>Start the RH measuring program by clicking on the&#160;Start&#160;button, entering the file name, and clicking the&#160;Save&#160;button to record the RH data.</li>
	</ol>
	</li>
	<li>Mass and dynamic shape factor of the SOM particles
	<ol>
		<li>Connect the outlet of the relative humidity control setup to the inlet of a differential mobility analyzer (DMA) with a three-feet-long electrostatic-resistant tubing. Connect the outlet of the DMA to the inlet of the APM instrument by one-feet-long electrostatic-resistant tubing. Connect the outlet of the APM to a condensation particle counter (CPC). 
		NOTE: The detailed operating procedures or troubleshooting of the DMA and CPC can be found in its manual.</li>
		<li>Turn on the APM instrument and the APM control box by pressing the respective power buttons. Click&#160;Remote&#160;button on the APM control box so that the instrument can be operated from the software interface in the computer.</li>
		<li>Turn on the APM control software. Load a pre-set scanning file by clicking the&#160;File&#160;and&#160;Load&#160;buttons (Figure 6).</li>
		<li>Click on the&#160;Start&#160;button of the APM control software so that the APM instrument starts to collect data.</li>
	</ol>
	</li>
	<li>Particle collection from the flow tube reactor
	<ol>
		<li>Connect the flow tube outlet to a nanometer aerosol sampler (NAS) by a three-feet-long electrostatic-resistant tubing.</li>
		<li>Clean a silicon substrate (prime grade, resistance 1-10 &#937;&#8729;cm) by a cycle of methanol, water, and again methanol. Dry the substrate using a gentle flow of nitrogen.</li>
		<li>Place the cleaned substrate onto the electrode of the NAS. Secure the edge of the substrate with tape to keep it stable during the collection22.</li>
		<li>Turn on the NAS. Set the voltage to -9.9 kV. Set the flow rate to 1.8 Lpm.</li>
		<li>Turn on the sampling instrument to run for 12-36 h. Afterwards, remove the silicon substrate loaded with collected particles from the NAS. Perform further analysis of particles on the substrate, such as morphology by SEM7&#160;or surface analysis9.</li>
	</ol>
	</li>
</ol>

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The authors declare no competing financial interests.

By adjusting the conditions in the flow tube reactor, a wide range of SOA particles with well-defined number concentrations and mass concentrations can be produced. The growth mechanism can also be altered between the condensational growth and coagulative growth modes, forming particles with different shapes. The critical steps in the protocol include maintaining a relative stable temperature of the flow tube reactor, and stabilizing the ozone concentration out of the ozone generator. It is also important to note that the position of the movable injector needs to be carefully recorded every time so that the residence time would stay the same when repeating the experiments.
If the particle concentration from the flow tube reactor seems to be different than expected, several troubleshooting procedures can be performed. An air-tight examine of the flow tube reactor can be performed first. Following the airtight exam, the number-diameter measurement instrument needs to be checked in order to exclude all the potential malfunction possibilities such as clogging at the inlet and depletion of 1-butanol solution for CPC.
Hence, the flow tube reactor described above is a useful tool for studying the physicochemical properties and evolution of the organic aerosols spanning a wide range of concentrations. Compared with other aerosol generation systems, the flow tube reactor can quickly produce aerosol particles for a variety of particle number and mass concentrations13, which is especially useful in high mass-loading sampling. The flow tube reactor is also equipped with a movable sampler, enabling study on the evolution and growth of the aerosol particles. On the other hand, the reactor has a relatively short residence time and a relatively high precursor concentration, which limits its ability to simulate close-to-ambient reaction conditions. Future work involving the flow tube reactor is to add ultraviolet illumination onto the inner walls so that photo-oxidation reactions can be conducted within the flow tube reactor. Plans are in place for other VOC reactants, such as &#946;-caryophyllene and limonene, to be studied as well24.

Volatile organic compounds (VOCs) emitted from the biosphere and anthropogenic activities undergo reactions in the atmosphere with oxidants (such as ozone or OH radicals) to produce secondary oxygenated compounds1,2. Some of these compounds, due to their low volatility, ultimately contribute to the mass concentration of atmospheric PM1,3,4. Atmospheric particles have important effects on climate, human health, and visibility5. The production mechanisms of organic PM, however, remain insufficiently characterized and understood, both qualitatively and quantitatively, to predict number and mass concentrations as well as physical and chemical properties. One approach for bridging this knowledge gap is to perform laboratory studies that use flow tube reactors for mimicking the production processes of atmospheric organic PM, thereby facilitating mechanistic, process, and characterization studies of the PM6,7,8,9,10,11,12. The flow tube reactor enables the rapid synthesis of aerosol particles for a variety of particle number and mass concentrations13.
The present study describes, through the use of video material, the production of organic PM as submicron-sized particles from the ozonolysis of a dominant atmospheric monoterpene (viz. &#945;-pinene) in a flow tube reactor, which was first described in Shrestha et al.13 Briefly, the flow tube was made of glass with an inner diameter of 48.2 mm and a length of 1.30 m. The flow tube was operated slightly above ambient pressure in the laminar flow regime (Reynolds number of 9.4 &#177; 0.5), and with a residence time of 38 &#177; 1 s 14. The temperature was set to be 25 &#177; 1 &#176;C by using a recirculating chiller to flow water in a double-layered customized box that housing the flow tube reactor.
A schematic plot of the flow tube reactor system is shown in Figure 1. A pure air generator is used to generate ultra-pure air that passes through an ozone generator, producing 200-500 ppm of ozone. An additional flow of pure air at 0.50 sLpm is used to evaporate &#945;-Pinene injected by a syringe injector in a round bottom flask. &#945;-Pinene is pre-mixed with 2-butanol at a dilution ratio of 1:5015,16,17 before being withdrawn to the syringe injector, because 2-butanol can act as an OH scavenger to ensure that ozonolysis was the only reaction occurring inside the flow tube. The round bottom flask was heated to 135 &#177; 1 &#176;C allowing quick evaporation of the injected organic compounds. The &#945;-pinene and ozone flow inlets were also arranged perpendicular to each other to induce turbulence and rapid mixing at the injection point. The outlet of the flow tube was split between sample collection, size distribution measurements (by the scanning mobility particle sizer-SMPS), particle density measurement, and exhaust. Reaction conditions are varied to control the relative contribution of condensation compared to coagulation to particle growth. The output of the flow tube needs to have at least one line connecting to an open-air exhaust hood, to ensure that it is not possible to build up pressure inside the flow tube and the round bottom flask even under incorrect experimental conditions. The characteristics of the produced particle population can thereby be finely adjusted. The flow tube reactor is equipped with a movable sampler enabling sampling of the organic PM at different time points in its production. The number-diameter distribution of the produced particle population is measured at various length of the flow tube. An APM measures the particle mass distribution and the dynamic shape factor7,18,19, which gives information about the morphology and other physical properties of the produced particle population.20,21 Particles are also collected on a nanometer particle sampler for offline imaging by an SEM7,22. The implication is that the flow tube reactor is a suitable medium for performing ozonolysis experiments and fast online and offline analysis of the PM produced therein.

<table><tbody><tr><td>(-)-&amp;alpha;-pinene&amp;nbsp;</td><td>Sigma-Aldrich</td><td>305715</td><td></td></tr><tr><td>2-butanol&amp;nbsp;</td><td>Sigma-Aldrich</td><td>294810</td><td></td></tr><tr><td>5.00 mL syringe&amp;nbsp;</td><td>Hamilton</td><td>201300</td><td></td></tr><tr><td>Aerosol particle mass analyzer</td><td>Kanomax</td><td>3600</td><td></td></tr><tr><td>Condensational particle counter</td><td>TSI</td><td>3022</td><td></td></tr><tr><td>Differential mobility analyzer</td><td>TSI</td><td>3081</td><td></td></tr><tr><td>Heating mantle</td><td>Cole-parmer</td><td>WU-36225-10</td><td></td></tr><tr><td>Mass flow controller</td><td>MKS</td><td>M100B</td><td></td></tr><tr><td>Nafion tube</td><td>Perma Pure</td><td>MD-700-24F-1</td><td></td></tr><tr><td>Nanometer aerosol sampler</td><td>TSI</td><td>3089</td><td></td></tr><tr><td>Ozone generator</td><td>Jelight</td><td>600</td><td></td></tr><tr><td>Ozone monitor</td><td>Ecosensors</td><td>UV-100</td><td></td></tr><tr><td>Pressure sensor</td><td>Omega</td><td>PX409</td><td></td></tr><tr><td>RH sensor</td><td>Rotronic</td><td>60587161</td><td></td></tr><tr><td>Round-bottom, three neck flask</td><td>Aceglass</td><td>6944-04</td><td></td></tr><tr><td>Scanning electron microscope</td><td>Zeiss</td><td>N/A</td><td>Ultra plus FESEM</td></tr><tr><td>Scanning mobility particle sizer</td><td>TSI</td><td>3071A+3772</td><td>electrostatic classifier is model 3071A and the condensational particle ocunter is 3772</td></tr><tr><td>Silicon substrate</td><td>University Wafer</td><td>1707</td><td></td></tr><tr><td>Syringe Needle</td><td>Hamilton</td><td>90025</td><td>25 G, 2 inch</td></tr><tr><td>Syringe pump</td><td>Chemyx</td><td>Fusion Touch 200</td><td></td></tr><tr><td>Temperature sensor and software</td><td>National Instrument</td><td>USB-TC01</td><td></td></tr><tr><td>water circulator</td><td>Brinkmann</td><td>RC6</td><td></td></tr></tbody></table>

production and measurement of organic particulate matter in a flow tube reactor

Organic particulate matter (PM) is increasingly recognized as important to the Earth's climate system as well as public health in urban regions, and the production of synthetic PM for laboratory studies have become a widespread necessity. Herein, experimental protocols demonstrate approaches to produce aerosolized organic PM by &#945;-pinene ozonolysis in a flow tube reactor. Methods are described for measuring the size distributions and morphology of the aerosol particles. The video demonstrates basic operations of the flow tube reactor and related instrumentation. The first part of the video shows the procedure for preparing gas-phase reactants, ozonolysis, and production of organic PM. The second part of the video shows the procedures for determining the properties of the produced particle population. The particle number-diameter distributions show different stages of particle growth, namely condensation, coagulation, or a combination of both, depending on reaction conditions. The particle morphology is characterized by an aerosol particle mass analyzer (APM) and a scanning electron microscope (SEM). The results confirm the existence of non-spherical particles that have grown from coagulation for specific reaction conditions. The experimental results also indicate that the flow tube reactor can be used to study the physical and chemical properties of organic PM for relatively high concentrations and short time frames.

A matrix of reaction conditions is summarized in Table 1. There is a range of number and mass concentrations of organic PM that can be produced depending on the selected &#945;-pinene and ozone concentrations13. For instance, as shown in Table 1, when the ozone concentration is 43 ppm, varying the &#945;-pinene concentration from 0.125-100 ppm could produce (4.4 &#177; 0.6) &#215; 105 to (9.1 &#177; 0.3) &#215; 106 particles&#8729;cm3 and mass concentrations of 101 to 104 &#181;g&#8729;m-3, respectively.
The evolution of the dynamic characteristics of the particle population can be studied inside the flow tube reactor. By means of video demonstration, an experiment was conducted using 50 &#177; 1 ppm of ozone and 125 ppb of &#945;-pinene. The longitudinal position of the particle sampler inside the flow tube allowed sampling at various times from 3.0 &#177; 0.2 to 38 &#177; 1 s. Figure 7 shows the number-diameter distributions of the aerosol particle population for this experiment. The total number concentration and the mode diameter of the particles increased with the residence time. For a residence time of 3 s, no particles were detected. For longer residence times, a particle population was obtained and measured. The mode diameter increased from less than 10 nm to about 50 nm for an increase in residence time from 17 &#177; 0.5 s to 38 &#177; 1 s. The corresponding number concentration increased from (8.6 &#177; 0.5) &#215; 104 cm-3 to (2.56 &#177; 0.07) &#215; 105 cm3.
Examples of the number-mass distributions recorded in three replicate experiments by the APM setup are shown in Figure 8. The particle mass and mobility diameters were used to calculate the dynamic shape factor, &#967;, across particle subpopulation. The dynamic shape factor &#967; is the ratio of the drag force on an actual particle divided by the drag force experienced by a volume-equivalent sphere23. Shape factors of nearly spherical particles approach unity whereas highly aspherical particles have significantly larger shape factors. Figure 9 shows the dynamic shape factors of the particles exiting the flow tube at various mobility diameters and humidity levels. The respective &#967; values for &#60;5% RH were 1.21 &#177; 0.02, 1.09 &#177; 0.02, and 1.08 &#177; 0.02 (one-sigma uncertainty), suggesting that the particle populations were composed largely of non-spherical particles.
As the RH was increased, &#967; decreased for all three populations, reaching a final value of 1.02 &#177; 0.01 at 35% RH and corresponding within uncertainty to spherical particles. Figure 10 shows SEM images of the particles exposed to &#60;5% RH (left column) and 80% RH (right column). The images indicate that the non-spherical particles became round after exposure to high RH, as discussed in detail in Zhang et al.7. The results above indicate that the flow tube reactor is capable of performing various kinds of online and offline analysis.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55684/55684fig1v2.jpg" /> 
Figure 1. A schematic flow diagram of the flow tube reactor system. The red lines show the flow containing ozone, the light blue lines show the flow containing &#945;-pinene, and the dark blue lines show the flow of the organic PM. The APM system consist of a DMA, an APM, and a CPC that are connected together. This figure previously appeared in Shreatha et al.13 and is reproduced here with permission.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55684/55684fig2v2.jpg" /> 
Figure 2. Graphical user interface for the ozone monitoring and recording program.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/55684/55684fig3v2.jpg" /> 
Figure 3. Graphical user interface for the temperature monitoring and recording program.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/55684/55684fig4v2.jpg" /> 
Figure 4. Graphical user interface for the pressure monitoring and recording program.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/55684/55684fig5v2.jpg" /> 
Figure 5. Graphical user interface for the number-diameter distribution program. <a href="https://www.jove.com/files/ftp_upload/55684/55684fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/55684/55684fig6v2.jpg" /> 
Figure 6. Graphical user interface for the APM program.
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/55684/55684fig7v2.jpg" /> 
Figure 7. Size distribution of the particle population from the flow tube at different residence times. The total number concentrations for each size distribution are 1.69 &#215; 10-1, 7.50 &#215; 103, 8.58 &#215; 104, 2.00 &#215; 105, 2.33 &#215; 105, and 2.56 &#215; 105 particles cm-3 for residence times of 3, 10, 17, 25, 32, and 38 s, respectively. The shaded areas are the standard deviation of particle size distribution. This figure previously appeared in Shreatha et al.13 and is reproduced here with permission. <a href="https://www.jove.com/files/ftp_upload/55684/55684fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/55684/55684fig8v2.jpg" /> 
Figure 8. An example of the number-mass distribution, as measured using the DMA-APM system. Results of three replicate experiments are shown to demonstrate reproducibility. Two-sigma uncertainty is represented by the error bars, which are approximately the same size as the data markers. The lines represent fits of a normal distribution to the data. The abscissa is calculated based on the APM rotation speed and the voltage applied between the walls of the APM cylinders. The particles shown in the plot were produced from 700 ppb &#945;-pinene and 14 ppm ozone. A central mobility diameter of 126.0 nm was selected by the DMA. This figure previously appeared in Zhang et al.7&#160;and is reproduced here with permission. <a href="https://www.jove.com/files/ftp_upload/55684/55684fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/55684/55684fig9v2.jpg" /> 
Figure 9. Dynamic shape factor for increasing relative humidity. Panel A: Particles produced from 700 ppb &#945;-pinene and 14, 25, and 30 ppm ozone for particle populations having central mobility diameters of 126.0, 175.0, and 190.0 nm, respectively. The exposure time to relative humidity was 310 s. The error bars in each panel represent two sigma of standard deviation. This figure previously appeared in Zhang et al.7&#160;and is reproduced here with permission. <a href="https://www.jove.com/files/ftp_upload/55684/55684fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/55684/55684fig10v2.jpg" /> 
Figure 10. SEM images of the particles obtained from 700 ppb &#945;-pinene and sampled for a central mobility diameter of 180.0 nm. The aerosol particles were collected on the silica substrate for 12 h and then coated with 5 nm of Pt/Pd. The voltage for the electron beam was 5 kV, and the working distance was 2.3 mm. Column 1 shows dimer, trimer, and higher-order agglomerates of the granular monomers for &#60;5% RH. Red circles identify the monomers. Column 2 shows nearly spherical particles that were collected after exposure to 80% RH followed by drying to &#60;5% RH. This figure previously appeared in Zhang et al.7&#160;and is reproduced here with permission.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>O3 (ppm)</td>
			<td rowspan="4"></td>
			<td colspan="2" rowspan="4">0.15&#177;0.02</td>
			<td rowspan="4">0.9&#177;0.1</td>
			<td rowspan="4">5.7&#177;0.2</td>
			<td rowspan="4">43&#177;1</td>
			<td rowspan="4">194&#177;2</td>
		</tr>
		<tr>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-pinene</td>
		</tr>
		<tr>
			<td>(ppm)</td>
		</tr>
		<tr>
			<td rowspan="4">0.125 &#177; 0.003</td>
			<td>Num. Conc.</td>
			<td colspan="2">0</td>
			<td>(1&#177;1)&#215;102</td>
			<td>(1.0&#177;0.6)&#215;105</td>
			<td>(4.4&#177;0.6)&#215;105</td>
			<td>(3.2&#177;0.2)&#215;105</td>
		</tr>
		<tr>
			<td>Mass. Conc.</td>
			<td colspan="2">0</td>
			<td>(3&#177;5)&#215;10-2</td>
			<td>15&#177;5</td>
			<td>11&#177;3</td>
			<td>20&#177;2</td>
		</tr>
		<tr>
			<td>Mode Diameter</td>
			<td colspan="2">0</td>
			<td>22&#177;4</td>
			<td>60&#177;5</td>
			<td>35&#177;3</td>
			<td>34&#177;2</td>
		</tr>
		<tr>
			<td>Geo. St. Deviation</td>
			<td colspan="2">N/A</td>
			<td>1.2</td>
			<td>1.3</td>
			<td>1.3</td>
			<td>1.5</td>
		</tr>
		<tr>
			<td rowspan="4">1.00 &#177; 0.03</td>
			<td>Num. Conc.</td>
			<td colspan="2">0</td>
			<td>(3.1&#177;0.9)&#215;102</td>
			<td>(1.5&#177;0.2)&#215;105</td>
			<td>(5.5&#177;0.2)&#215;105</td>
			<td>(5.8&#177;0.4)&#215;105</td>
		</tr>
		<tr>
			<td>Mass. Conc.</td>
			<td colspan="2">0</td>
			<td>(9&#177;3)&#215;10-3</td>
			<td>61&#177;9</td>
			<td>(52&#177;0.1)&#215;102</td>
			<td>(66&#177;0.1)&#215;102</td>
		</tr>
		<tr>
			<td>Mode Diameter</td>
			<td colspan="2">0</td>
			<td>33&#177;7</td>
			<td>86&#177;6</td>
			<td>84&#177;3&#160;</td>
			<td>85&#177;19&#160;</td>
		</tr>
		<tr>
			<td>Geo. St. Deviation</td>
			<td colspan="2">N/A</td>
			<td>1.3</td>
			<td>1.4</td>
			<td>1.5</td>
			<td>1.7</td>
		</tr>
		<tr>
			<td rowspan="4">10.0 &#177; 0. 3</td>
			<td>Num. Conc.</td>
			<td colspan="2">(2&#177;2)&#215;101</td>
			<td>(4.0&#177;0.2)&#215;105</td>
			<td>(6.0&#177;0.7)&#215;105</td>
			<td>(6.3&#177;0.7)&#215;105</td>
			<td>(1.8&#177;0.2)&#215;106</td>
		</tr>
		<tr>
			<td>Mass. Conc.</td>
			<td colspan="2">0*</td>
			<td>(1.6&#177;0.2)&#215;102</td>
			<td>(2.5&#177;0.2)&#215;103</td>
			<td>(1.19&#177;0.02)&#215;104</td>
			<td>(1.57&#177;0.02)&#215;104</td>
		</tr>
		<tr>
			<td>Mode Diameter</td>
			<td colspan="2">8&#177;9</td>
			<td>81&#177;2</td>
			<td>147&#177;9</td>
			<td>245&#177;38</td>
			<td>155&#177;5</td>
		</tr>
		<tr>
			<td>Geo. St. Deviation</td>
			<td colspan="2">1</td>
			<td>1.4</td>
			<td>1.4</td>
			<td>1.4</td>
			<td>1.5</td>
		</tr>
		<tr>
			<td rowspan="4">100 &#177; 3</td>
			<td>Num. Conc.</td>
			<td colspan="2">(4.4&#177;0.3)&#215;105</td>
			<td>(8.3&#177;0.3)&#215;105</td>
			<td>(8.3&#177;0.4)&#215;106</td>
			<td>(9.1&#177;0.2)&#215;106</td>
			<td>(1.3&#177;0.02)&#215;107</td>
		</tr>
		<tr>
			<td>Mass. Conc.</td>
			<td colspan="2">35&#177;3</td>
			<td>(8.6&#177;0.1)&#215;102</td>
			<td>(1.3&#177;0.1)&#215;104</td>
			<td>(1.6&#177;0.04)&#215;105</td>
			<td>(4.0&#177;0.1)&#215;105</td>
		</tr>
		<tr>
			<td>Mode Diameter</td>
			<td colspan="2">48&#177;2</td>
			<td>88&#177;5&#160;</td>
			<td>134&#177;8</td>
			<td>262&#177;12</td>
			<td>334&#177;4</td>
		</tr>
		<tr>
			<td>Geo. St. Deviation</td>
			<td colspan="2">1.4</td>
			<td>1.6</td>
			<td>1.5</td>
			<td>1.7</td>
			<td>1.9</td>
		</tr>
	</tbody>
</table>
Table 1. Number concentrations (cm-3), mass concentrations (&#181;g m-3), mode diameter (nm), and geometric diameter standard deviation of the particles produced by &#945;-pinene ozonolysis. A material density of 1200 kg&#8729;m3 was used for conversion of volume concentrations to mass concentrations and the residence time was 38 s for all experiments. *Although particles were present, the mass concentration was below the detection limit. This table previously appeared in Shreatha et al.13 and is reproduced here with permission.

Watch this Scientific Journal Video about Production and Measurement of Organic Particulate Matter in a Flow Tube Reactor at JoVE.com

Production and Measurement of Organic Particulate Matter in a Flow Tube Reactor

This paper describes the operation procedure for the flow tube reactor and related data collection. It shows the protocols for setting the experiments, recording data and generating the number-diameter distribution as well as the particle mass information, which gives useful information about chemical and physical properties of the organic aerosols.

Organic particulate matter (PM) is increasingly recognized as important to the Earth's climate system as well as public health in urban regions, and the ...

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JoVE Journal

Environment

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Video: Production and Measurement of Organic Particulate Matter in a Flow Tube Reactor

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Agricultural ammonia (NH3) emissions (90% of total EU emissions) are responsible for about 45% airborne eutrophication, 31% soil acidification and 12% fine dust formation within the EU15. But NH3 emissions also mean a considerable loss of nutrients. Many studies on NH3 emission from organic and mineral fertilizer application have been performed in recent decades. Nevertheless, research related to NH3 emissions after application fertilizers is still limited in particular with respect to relationships to emissions, fertilizer type, site conditions and crop growth. Due to the variable response of crops to treatments, effects can only be validated in experimental designs including field replication for statistical testing. The dominating ammonia loss methods yielding quantitative emissions require large field areas, expensive equipment or current supply, which restricts their application in replicated field trials. This protocol describes a new methodology for the measurement of NH3 emissions on many plots linking a simple semi-quantitative measuring method used in all plots, with a quantitative method by simultaneous measurements using both methods on selected plots. As a semi-quantitative measurement method passive samplers are used. The second method is a dynamic chamber method (Dynamic Tube Method) to obtain a transfer quotient, which converts the semi-quantitative losses of the passive sampler to quantitative losses (kg nitrogen ha-1). The principle underlying this approach is that passive samplers placed in a homogeneous experimental field have the same NH3 absorption behavior under identical environmental conditions. Therefore, a transfer co-efficient obtained from single passive samplers can be used to scale the values of all passive samplers used in the same field trial. The method proved valid under a wide range of experimental conditions and is recommended to be used under conditions with bare soil or small canopies (&#60;0.3 m). Results obtained from experiments with taller plants should be treated more carefully.

Calibrated Passive Sampling - Multi-plot Field Measurements of NH3 Emissions with a Combination of Dynamic Tube Method and Passive Samplers

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The production and the evolution of atmospheric organic particulate matter (PM) are insufficiently understood for accurate simulations of atmospheric chemistry and climate. The complex production mechanisms and reaction pathways make this a challenging research topic. To address these issues, an environmental chamber, providing enough residence time and close-to-ambient concentrations of precursors for secondary organic materials, is needed. The Harvard Environmental Chamber (HEC) was built to serve this need, simulating the production of gas and particle phase species from volatile organic compounds (VOCs). The HEC has a volume of 4.7 m3 and a mean residence time of 3.4 h under typical operating conditions. It is operated as a completely mixed flow reactor (CMFR), providing the possibility of indefinite steady-state operation across days for sample collection and data analysis. The operation procedures are described in detail in this article. Several types of instrumentation are used to characterize the produced gas and particles. A High-Resolution Time-of-Fight Aerosol Mass Spectrometer (HR-ToF-AMS) is used to characterize particles. A Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) is used for gaseous analysis. Example results are presented to show the use of the environmental chamber in a wide variety of applications related to the physicochemical properties and reaction mechanisms of organic atmospheric particulate matter.

This paper describes operation procedures for the Harvard Environmental Chamber (HEC) and related instrumentation for measuring gaseous and particle species. The environmental chamber is used to produce and study secondary organic species produced from the organic precursors, especially related to atmospheric organic particulate matter.

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We demonstrate a versatile protocol to be used for determining the effectiveness of photocatalysts in degrading indoor air concentration (ppb) volatile ...

Lab-Scale Model to Evaluate Odor and Gas Concentrations Emitted by Deep Bedded Pack Manure

A lab-scaled simulated bedded pack model was developed to study air quality and nutrient composition of deep-bedded packs used in cattle mono-slope facilities. This protocol has been used to effectively evaluate many different bedding materials, environmental variables (temperature, humidity), and potential mitigation treatments that can improve air quality in commercial deep-bedded mono-slope facilities. The model is dynamic and allows researchers to easily collect many chemical and physical measurements from the bedded pack. Weekly measurements, collected over the course of six to seven weeks, allows sufficient time to see changes in air quality measurements over time as the bedded pack matures. The data collected from the simulated bedded packs is within the range of concentrations previously measured in commercial deep-bedded mono-slope facilities. Past studies have demonstrated that 8 - 10 experimental units per treatment are sufficient to detect statistical differences among the simulated bedded packs. The bedded packs are easy to maintain, requiring less than 10 minutes of labor per bedded packs per week to add urine, feces, and bedding. Sample collection using the gas sampling system requires 20 - 30 minutes per bedded pack, depending on the measurements that are being collected. The use of lab-scaled bedded packs allows the researcher to control variables such as temperature, humidity, and bedding source that are difficult or impossible to control in a research or commercial facility. While not a perfect simulation of &#34;real-world&#34; conditions, the simulated bedded packs serve as a good model for researchers to use to examine treatment differences among bedded packs. Several lab-scale studies can be conducted to eliminate possible treatments before trying them in a research or commercial-sized facility.

A protocol has been developed to measure gases, odors, and nutrient composition in lab-scaled bedded manure packs, which can be used to study ways to improve air quality in commercial cattle facilities using deep-bedded manure packs.

A lab-scaled simulated bedded pack model was developed to study air quality and nutrient composition of deep-bedded packs used in cattle mono-slope ...

A System to Create Stable Nanoparticle Aerosols from Nanopowders

Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring minimal amounts of test materials (min. 200 mg), for studying powder aerosolization behavior and aerosol properties. The aerosolization procedure follows the concept of the fluidized-bed process, but occurs in the modified volume of a V-shaped aerosol generator. The airborne particle number concentration is adjustable by controlling the air flow rate. The system supplied stable aerosol generation rates and particle size distributions over long periods (0.5-2 hr and possibly longer), which are important, for example, to study aerosol behavior, but also for toxicological studies. Strict adherence to the operating procedures during the aerosolization experiments ensures the generation of reproducible test results. The critical steps in the standard protocol are the preparation of the material and setup, and the aerosolization operations themselves. The system can be used for experiments requiring stable aerosol concentrations and may also be an alternative method for testing dustiness. The controlled aerosolization made possible with this setup occurs using energy inputs (may be characterized by aerosolization air velocity) that are within the ranges commonly found in occupational environments where nanomaterial powders are handled. This setup and its operating protocol are thus helpful for human exposure and risk assessment.

We designed and developed an effective nanopowder aerosolization setup and operating protocol. The system generated nanoparticle aerosols with stable number concentrations and size distributions for long durations, requiring only small quantities of test material (min. 200 mg).

Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring ...

Engineering

Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional batch reactors, coined stop-flow micro-tubing (SFMT) reactors. In SFMT, chemical reactions that require high pressure can be screened in parallel through a safer and convenient way. Cross-contamination, which is a common problem in reaction screening for continuous flow reactors, is avoided in SFMT. Moreover, the commercially available light-permeable micro-tubing can be incorporated into SFMT, serving as an excellent choice for light-mediated reactions due to a more effective uniform light exposure, compared to batch reactors. Overall, the SFMT reactor system is similar to continuous flow reactors and more superior than batch reactors for reactions that incorporate gas reagents and/or require light-illumination, which enables a simple but highly efficient reaction screening system. Furthermore, any successfully developed reaction in the SFMT reactor system can be conveniently translated to continuous-flow synthesis for large scale production.

A protocol for organic reaction screening using stop-flow micro-tubing (SFMT) reactors employing gaseous reactants and/or visible-light mediated reactions is presented.

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

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.

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 ...

Additive Manufacturing-Enabled Low-Cost Particle Detector

As particles with a size of 1 &#181;m or smaller pose a severe health risk to the human body, the detection and regulation of particle emissions are of great importance. A large share of particulate emissions are emitted by the transport sector. Most of the commercially available particle detectors are bulky, very expensive, and need additional equipment. This paper presents a protocol to build and test a standalone particle detector that is small and cost-efficient. 
The focus of this paper lies in the description of the detailed construction manual with video and the sensor evaluation procedure. The computer-aided design model of the sensor is included in the supplemental material. The manual explains all the construction steps, from 3D printing to the fully operational sensor. The sensor can detect charged particles and is therefore suitable for a wide range of applications. A possible field of application would be soot detection from power plants, wildfires, industries, and automobiles.

Here, we present a protocol on how to build and test a simple but efficient low-cost particle detector.

As particles with a size of 1 &#181;m or smaller pose a severe health risk to the human body, the detection and regulation of particle emissions are of ...

Production and Measurement of Organic Particulate Matter in a Flow Tube Reactor

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