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A U T H O R

Lindsay D. Yee

Environmental Engineering

Lindsay yee is a graduating senior in

Environmental Engineering. Her research

interests are in air quality, with an

emphasis on secondary organic aero-

sols (SOA), a major contributor to fine

particulate matter. She has conducted

four years of undergraduate research

investigating SOA formation using the

environmental chamber at the College

of Engineering Center for Environmental

Research and Technology (CE-CERT).

Her academic research interests and her

outreach efforts through the Society of

Women Engineers led to her selection as

a National Science Foundation Graduate

Research Fellow. yee will expand on her

research pursing a Ph.D. at the California

Institute of Technology in fall of 2008.

A B S T R A C T

A large portion of California’s economy is based on agriculture, which depends on heavy use of pesticides to limit the amount of crop damage from insects, fungi, and unwanted weed growth. Pesticides are known to have direct health effects on humans. In this work, we investigate their potential to react within the atmosphere to form ozone and secondary organic aerosols (SOA). A series of photo-oxidation experiments were conducted within dual 90m3 reactors of our environmental chamber. Individual pesticides were added to a surrogate volatile organic compound (VOC)/nitrogen oxides (NOx) mixture and were irradiated with a 200 kW Argon arc-lamp to study increased ozone formation and SOA production. The gas surrogate consists of ethene, propene, n-butane, trans-2-butene, toluene, octane, and m-xylene. The pesticide compounds tested include carbon disulfide (CS2), kerosene, 1-3-dichloropropenes, S-ethyl N, N-di-n-propyl thiocarbamate (EPTC), and methyl isothiocyanate (MITC). Initial results show that some pesticides (i.e. EPTC, kerosene) increased SOA formation up to ten times over the base case surrogate mixture, while decreasing the ozone formation. Other pesticides (i.e. CS2, MITC) increased the SOA formation by as much as twelve times in the surrogate mixture while increasing ozone levels.

F A C U L T Y m e n T o R

David CockerDepartment of Chemical and Environmental EngineeringLindsay Yee joined our research group as a Research Advancement Program (RAP) scholar upon entering her freshman year at UC Riverside. Her academic and research skills are exceptional and she is a true pleasure to work with in the lab. Her undergraduate research has focused on estimating secondary organic aerosol formation (SOA), which is fine particle formed within the atmosphere from gaseous organic precursors. This current work reflects her investigation of the atmospheric chemistry of agricultural pesticides and their propensity to form fine particles – important from an air quality perspective as well as in the transport and environmental fate of such compounds.

Lindsay D. Yee, Bethany A. Warren, David R. Cocker IIIDepartment of Chemical and Environmental Engineering University of California, Riverside

Secondary Organic Aerosol (SOA) And Ozone Formation From Agricultural Pesticides

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SECONDARy ORGANIC AEROSOL (SOA) AND OZONE FORMATION FROM AGRICULTURAL PESTICIDES

Lindsay D. Yee

Introduction

California Agriculture relies heavily on the use of chemical pesticides as insecticides, fungicides, and herbicides for crop protection and production. While pesticides have been studied for their adverse effects on human health, little has been studied regarding their reactivity in the atmosphere. Previous pesticide atmospheric studies conducted by Carter et al. have looked at the reactivity of pesticides like methyl bromide and chloropicrin . The goal of this case study was to look at the possible fate of a new group of selected pesticides in the atmosphere through secondary reactions. Simulated atmospheric reactions in the presence of a pesticide allowed for quantitative measure of the additional reactivity that each pesticide contributed to the system in terms of the additional ozone and secondary organic aerosol formed.

Five pesticides of interest to the California Air Resources Board were tested in this work: 1,3-dichloropropenes (trade name Telone®), Carbon disulfide (CS2), S-Ethyl N,N-di-n-propyl thiocarbamate (EPTC), Kerosene, and Methyl Isothiocyanate (MITC). 1,3-dichloropropenes are often planted with crops to fight nematodes2. CS2 is applied to nuts, apples, and other fresh fruit crops while EPTC is often applied to potatoes, corn, peas, and alfalfa as an herbicide for weed management. Kerosene is often applied as an oil pesticide for insecticide use on the almond, avocado, cotton, grape, lemon, and cauliflower crops3. MITC is another common soil fumigant, on the EPA’s list of high volume chemicals for being produced in over 1 million pounds per year4.

When a reactive organic gas (ROG) undergoes photo-oxidation in the atmosphere reacting with an oxidizing agent like ozone, hydroxyl radical, or nitrate radical, a myriad of products are formed. Some with higher vapor pressure remain in the gas phase while others with lower vapor pressure condense and become secondary organic aerosol. Within the surrogate mixture used in the experiment, the ROGs are the aerosol forming aromatic hydrocarbons, m-xylene or toluene.

Fine particulate matter, defined as particles with diameter less than 2.5 μm (PM2.5), adversely affects human health5, 6,decreases visibility7, 8, damages property, and affects global climate change9. SOA can contribute significantly to atmospheric PM2.5. In fact, it was estimated that it can

contribute up to 70% of fine particulate matter (PM2.5) in urban air sheds10. Tropospheric ozone formation results from photochemical reactions of volatile organic compounds (VOCs) in the presence of nitrous oxides (NOx)

11. High ozone levels at ground level also remain a human health concern as it causes many respiratory problems 12.

A surrogate gas mixture with known ozone and SOA formation potential can be used to study the effects of each selected pesticide when added to the system. A surrogate mixture was developed by Carter et. al to emulate urban atmospheric reactivity15. In the presence of a pesticide, changes in the chemical mechanisms and pathways are anticipated, resulting in final ozone and SOA concentrations different from the surrogate profile. While the scope of this work does not extend to the actual mechanisms behind the results, initial determination of a pesticide as an ozone or SOA enhancing or depressing agent under the experimental conditions was gained. Further parameters of changes in particle count and particle size were also determined to gain a greater understanding of each pesticide’s effects on SOA characteristics.

Results

Experimental results from five representative pesticide experiments are presented here. A summary of the results can be found in Table 1.

Final ozone concentration in parts per billion by volume (ppb), mass volume of particles in micrograms per cubic meter (µg/m3), count of particles, and diameter of particles were recorded. The final volume was calculated from the raw data collected by the SMPS, including a correction which accounts for particle losses on the walls of the reactors15. As shown in Table 1, each run utilizes one side (indicated as A or B) of the dual reactors strictly for the surrogate mixture, while the other side is used for the surrogate mixture with a pesticide added. For example, in Run 554, Side A only contained the surrogate mixture and Side B contained the same concentration of surrogate as Side A plus 103ppb of dichloropropenes. This method allowed for direct comparison of the surrogate versus surrogate plus pesticide results.

Effects on Ozone FormationFigure 1 shows the ozone formation during

experiment from the time the light source is turned on

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(Time = 0) to the time the light source is turned off for the surrogate mixture. Ozone formation profiles for the arc light (dashed trend lines) and black light (solid trend lines) surrogate experiments are established here. The difference in these profiles results from the differing light intensity of the Argon arc light and black light sources available to initiate the photochemistry and ozone formation. The ozone results of the arc light surrogate plus pesticide experiments are directly compared to the surrogate profile shown in Figure 2, revealing dichloropropenes as an ozone forming enhancer by about 20 ppb in Run 554, and EPTC as an ozone depressant by 11 ppb in Run 590. For the pesticides run under black light conditions (Figure 3), ozone formation decreased in the presence of kerosene by 11 ppb in Run 602, while CS2 increased ozone by 15 ppb in Run 597. Most dramatic was the near seven fold increase of ozone formation in the presence of MITC from 54 ppb to 362 ppb in Run 599. The difference in ozone surrogate profiles by light source does not allow for direct comparison of all the pesticides to establish a relative order of ozone enhancing potential; however, each pesticide was identified as either an ozone enhancer or ozone depressant.

Effects on SOA FormationFigure 5 (see page 72) presents the ozone and SOA

formation for each pesticide run. SOA is shown as a mass concentration of SOA formation during experiments. Total aerosol mass formed was calculated from the final particle size distribution, after wall loss correction, and assuming unit density13. In the case of SOA formation, all surrogate only experiments had the same SOA profile regardless of

Run Light PesticidePesticide

Added O3 Final (ppb)

PM Final Volume (μg/m3)

PM Final Count

Final Diameter (nm)

554A Arc None 0 ppb 146 7.8 31700 60

554B Arc Dichloropropenes 103 ppb 165 7.0 29000 62

590A Arc None 0 ppb 140 6.9 25100 118

590B Arc EPTC 250 ppb 129 51.0 70900 76

597A BL None 0 ppb 118 6.8 21100 72

597B BL CS2 630 ppb 133 32.7 63500 97

599A BL MITC 990ppm 362 62.8 81100 112

599B BL None 0 ppb 54 5.1 16500 72

602A BL kerosene 1.0 ppmC 99 50.1 16000 192

602B BL None 0 ppmC 110 5.0 15300 79

Table 1. Results of the experiment in terms of final ozone concentration, mass concentration of SOA formed, particle count, and particle size (by diameter) is recorded below for each Run. Under the “Light” column, Arc refers to the Argon arc lamp and BL refers to the black lights being used for that particular run.

Ozone Formation from Surrogate by Light Source

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Figure 1. Ozone formation profiles for the surrogate gas mixture under the Argon arc light source and Black light source. Each run has a surrogate ozone formation profile shown. Ozone formation potential is higher under the arc light for the surrogate gas mixture; this is due to differing intensities of the light sources.

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SOA Formation

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light source used. This allows for a direct comparison of all pesticides in terms of their particle formation potential (Figure 4).

Clearly, all the pesticides enhanced SOA formation except for dichloropropenes, where no significant difference from the surrogate was observed. CS2 caused an almost five

times increase in SOA and the particle count tripled. The diameter of the particles also increased by 25 nm, suggesting that CS2 has increased the number of particles formed as well as their size (Table 1). Yet, while EPTC depressed ozone formation (Figure 5, see page 72), the SOA mass concentration was seven times larger and particle count was

Ozone Formation from Arc Light Experiments

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Figure 2. Ozone formation in the presence of Dichloropropenes and EPTC compared to the 1.1 ppmC Surrogate only.

Figure 3. Kerosene was the only pesticide run under black light conditions to result in lower ozone than the surrogate base case.

Figure 4. The volume of SOA formed during experiment is shown for all runs for overall comparison. This comparison can be made because the SOA formed by the surrogate mixture alone is the same regardless of light source, as shown by the overlapping surrogate SOA profiles for all five runs. The graphical analysis allows for a predicted trend of lowest to highest SOA formation potential amongst the tested pesticides, determined as: dichloropropenes, CS2, EPTC, kerosene, and MITC.

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almost tripled. In addition, diameter size of the particles in the presence of EPTC was smaller (Table 1). It is possible that a large nucleation burst at the onset of particle formation led to the lower final diameter achieved in the presence of EPTC. Kerosene, on the other hand, while decreasing ozone slightly has ten times the SOA mass concentration (Figure 5, see page 72) while maintaining a close particle count but with increased diameter size (Table 1). MITC had very dramatic and direct impacts on the surrogate system, putting out ozone concentrations seven times higher and an aerosol mass concentration twelve times higher (Table 1, Figure 5). In the presence of MITC particle count was a staggering 81,100 cm-3 compared to 16,500 cm-3 and they were significantly larger too (Table 1). In addition, SOA formed within 50 minutes of the experiment, compared to around 100 minutes for the surrogate base as seen in the MITC SOA plot in Figure 5 (see page 72). MITC could be initiating SOA formation pathways earlier with nucleation and/or even serving as a reactive organic gas to directly react and contribute to the SOA yield. It could also be affecting kinetics of the reaction.

Discussion

These preliminary results suggest that many of these agricultural pesticides impact the atmospheric chemistry that would normally occur from just the surrogate base. Reaction mechanisms and pathways could be altered, bypassed, or changed completely in the presence of a pesticide. Reaction kinetics and timing of nucleation could be affected, as in the case of MITC, EPTC, and CS2. The number and physical properties of the particles formed were also changed. All of these properties are related to their atmospheric transport. Moreover, there is no direct correlation or predictor that a pesticide affects ozone formation in the same direction it does for SOA formation. A pesticide independently impacts the yields of ozone and particulate matter formed. Yet a trend of lowest to highest SOA forming potential was proposed. The results of this study, in addition to the quantified maximum incremental reactivity as determined by Carter and Malkina14 for these pesticides, could serve as motivation for new limitations on the use of certain pesticides in order to meet federal and state air quality standards. Future work would include further investigation into the reasons behind these trends.

Further experimental detail on all the pesticide experiments completed can be found in Carter and Malkina14.

Materials and Methods

UC Riverside/CE-CERT Environmental ChamberThe experiments were performed using the UC

Riverside/CE-CERT Environmental Chamber, consisting of dual 90m3 reactors made from 2 mil FEP Teflon® film. Pure air from an AADCO® air purification system (NOx <10ppt, <0.2 particles) is cycled through the chamber prior to commencing experiments. The enclosure is maintained at a constant temperature of 27°C ±1°C. The framework that holds the Teflon reactors moves down during the experiment to maintain a 0.025” H2O positive pressure compared to the enclosure pressure as air is withdrawn from the reactors. A 200kW Argon arc lamp with a UV and visible spectra very similar to the sun was used for some experiments. Other experiments were performed using banks of 115W Sylvania 350BL black lights. The selected light source provided the energy to initiate the photochemistry. The pesticide was injected into the reactor via a heated injection tube under a stream of purified nitrogen. The liquid surrogate compounds were also injected this way. The ethene, propene, n-butane, trans-2-butene, toluene, octane, and m-xylene gas surrogate compounds were directly injected from a certified gas cylinder at a flow of 900cc/min for 10.75 minutes. Injection bulbs of known volume were filled to the necessary pressure of NO and NO2 and injected through the injection tube as well. More information on the environmental chamber can be found in Carter et al.15

Gas Phase SamplingA Hewlett-Packard 5890 Series II gas chromatograph

with a DB-5 column and flame ionization detector (FID) was used to track the decaying concentrations of m-xylene, toluene, MITC, and the dichloropropenes. Another GC-FID, HP 5890 Series II was utilized with a Tenax sample cartridge to monitor EPTC as well as MITC and dichloropropenes. A Dasibi Model 1003-AH Model 8410 Ozone Analyzer was used to track the ozone formation during the experiment, while a Teco Model42 C Analyzer was used to monitor NOx levels.

Particle Phase SamplingParticle size and number were determined using a

Scanning Mobility Particle Spectrometer (SMPS), built

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SOA from Dichloropropenes Run 554

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Figure 5. All pesticides were plotted over time in terms of their ozone formation and the volume concentration of SOA formed. Comparison of the ozone formation and SOA formation plots for each pesticide show that each pesticide independently affects ozone and SOA formation. For example, while kerosene depressed ozone formation, there was a dramatic increase in SOA formed in its presence.

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from a TSI model 88Kr neutralizer, a Dynamic Mobility Analyzer (DMA) TSI 3081 long column, and a TSI Model 3760 Condensation Particle Counter (CPC). The SMPS was located within the chamber enclosure and pulled three samples per side at a 60 second scan rate. The column was ramped from -40 to -7000 V to monitor particle diameters from 28-730 nm. The DMA air flows consisted of 2.5 L min-1 for sheath and excess flows and 0.25 L min-1 for aerosol and monodisperse flows.

Use of the SurrogateA case study of the pesticide effects on the 25ppb

NOx (1/3 NO2, 2/3 NO), 1.1ppmC surrogate runs was performed. The surrogate mixture contained ethene, propene, n-butane, trans-2-butene, toluene, octane, and m-xylene. Experiments were run by injecting surrogate in both reactors and then injecting atmospherically relevant concentrations of pesticide into only one reactor. This allowed for a direct comparison of the SOA and ozone formation profiles for the surrogate-only reactor to the surrogate plus pesticide reactor.

Acknowledgements

We gratefully acknowledge funding from National Science Foundation CAREER 0449778 and California Air Resources Board Contract No. 04-334 for support of this project. We thank Kurt Bumiller, Irina Malkina, and William P.L. Carter for their knowledge, design, and expertise in conducting these experiments.

References

Carter, W. P. L., D. Luo and I. L. Malkina (1997b): 1. Investigation of that Atmospheric Reactions of Chloropicrin,” Atmos. Environ. 31, 1425-1439.EPA. R.E.D. Facts 1,3-Dichloropropene; 2. EPA/787/F/98/014; Environmental Protection Agency: Washington, DC, 1998.Department of Pesticide Regulation. 3. Summary of Pesticide Use Report Data 2005 Indexed by Chemical; California Environmental Protection Agency: Sacramento, CA, 2006. Scorecard The Pollution Information Site. Chemical 4. Profile for METHYL ISOTHIOCYANATE (CAS Number: 556-61-6), http://www.scorecard.org.Schwartz, J.; Dockery, D.W.; Neas, L.M.; et al. Is daily 5. mortality associated specifically with fine particles? J. Air Waste Manage. Assoc. 1996, 46, 927-39.EPA. 6. Air Quality Criteria for Particulate Matter; EPA/600/P-95/001cF; Environmental Protection Agency: Washington, DC, 1996.Eldering, A.; Cass, G.R. Source-oriented model for air 7. pollutant effects on visibility. J. Geophy. Res. 1996, 101, 19343-19369.Larson, S. M; Cass, G.R. Characteristics of summer 8. midday low-visibility events in the Los Angeles area. Environ. Sci. Technol. 1989, 23 (3), 281-289.Pilinis, C.; Pandis, S.; Seinfeld, J.H. Sensitivity of 9. direct climate forcing by atmospheric aerosols to aerosol size and composition. J. Geophys. Res. 1995, 100, 18739-18754.

SOA from MITC Run 599

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Turpin, B.J.; Huntzicker, J.J. Secondary formation 10. of organic aerosol in the Los-Angeles basin—a descriptive analysis of organic and elemental carbon concentrations. Atmos. Environ. 1991, 25A (2), 207-215.Seinfeld, J.H.; Pandis, S.N.; 11. Atmospheric Chemistry and Physics: from Air Pollution to Climate Change; J. Wiley: Hoboken, N.J., 2006; 2nd ed.Environmental Protection Agency. Ground-level 12. ozone: Health and the Environment, http://www.epa.gov/air/ozonepollution/health.html Forstner, H.J.L.; Flagan, R.C.; Seinfeld, J.H. Secondary 13. organic aerosol from the photooxidation of aromatic hydrocarbons: molecular composition. Environ. Sci. Technol. 1997, 31, 1345-1358.

Carter, W. P. L.; Malkina, I. L. 14. Investigation of Atmospheric Ozone Impacts of Selected Pesticides; Final Report to the California Air Resources Board; Contract No. 04-334; 2007.Carter, W. P. L.; Cocker, D. R., III; Fitz, D. R.; 15. Malkina, I. L.;Bumiller, K.; Sauer, C. G.; Pisano, J. T.; Bufalino, C.; Song, C. A new environmental chamber for evaluation of gas- phase chemical mechanisms and secondary aerosol formation. Atmos. Environ. 2005, 39, 7768-7788.