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Papers by michael ezell

The Journal of Physical Chemistry, 1987

The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast f... more The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast flow discharge system using the reaction of hydrogen atoms with NOz as the source of OH. The decay of OH in excess ClNO at a total pressure of 1.05 0.05 Torr in He was followed by resonance fluorescence. at 309.5 nm at temperatures from 262 to 373 K in 2.4-cm-diameter flow tubes coated with boric acid, phosphoric acid, or halocarbon wax. Kinetic studies were also carried out in a 4.8-cm-diameter boric acid coated flow tube. While the rate of decay of OH increased both above and below room temperature in both boric acid coated flow tubes, more typical Arrhenius behavior was observed in the phosphoric acid and halocarbon wax coated tubes. The stable products observed by mass spectrometry from 276 to 353 K and from 0.2 to 0.8 Torr total pressure were HOCl, HONO, and CIz, which supports the existence of two reaction channels suggested in earlier work by Poulet and co-workers (1981): OH + ClNO-HOCl + NO (la), OH + ClNO-HONO + C1 (lb). Molecular CIz results from the reaction of Cl atoms with the excess ClNO present. The ratio of the products HOC1/ClZ did not change significantly with temperature or total pressure. All of these data taken together indicate that the temperature dependence observed in the boric acid coated flow tubes is due to an unusual surface reaction rather than intermediate complex formation in reaction 1 b. Taking only the data for which the surface reaction is believed to be negligible, the Arrhenius expression for the rate constant kl (= k l , + klb) for the reaction of OH with ClNO is kl = (1.5T; X exp[-(458 f 2 7) / a cm3 molecule-' s-l, with kl = (3.2 0.5) X cm3 molecule-' s-' at 298 K, where all errors are two standard deviations. From these kinetic data, a typical tropospheric lifetime of ClNO with respect to reaction with OH is calculated to be-36 days, too slow to compete with ClNO photolysis.

The Journal of Physical Chemistry, 1987

The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast f... more The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast flow discharge system using the reaction of hydrogen atoms with NOz as the source of OH. The decay of OH in excess ClNO at a total pressure of 1.05 0.05 Torr in He was followed by resonance fluorescence. at 309.5 nm at temperatures from 262 to 373 K in 2.4-cm-diameter flow tubes coated with boric acid, phosphoric acid, or halocarbon wax. Kinetic studies were also carried out in a 4.8-cm-diameter boric acid coated flow tube. While the rate of decay of OH increased both above and below room temperature in both boric acid coated flow tubes, more typical Arrhenius behavior was observed in the phosphoric acid and halocarbon wax coated tubes. The stable products observed by mass spectrometry from 276 to 353 K and from 0.2 to 0.8 Torr total pressure were HOCl, HONO, and CIz, which supports the existence of two reaction channels suggested in earlier work by Poulet and co-workers (1981): OH + ClNO-HOCl + NO (la), OH + ClNO-HONO + C1 (lb). Molecular CIz results from the reaction of Cl atoms with the excess ClNO present. The ratio of the products HOC1/ClZ did not change significantly with temperature or total pressure. All of these data taken together indicate that the temperature dependence observed in the boric acid coated flow tubes is due to an unusual surface reaction rather than intermediate complex formation in reaction 1 b. Taking only the data for which the surface reaction is believed to be negligible, the Arrhenius expression for the rate constant kl (= k l , + klb) for the reaction of OH with ClNO is kl = (1.5T; X exp[-(458 f 2 7) / a cm3 molecule-' s-l, with kl = (3.2 0.5) X cm3 molecule-' s-' at 298 K, where all errors are two standard deviations. From these kinetic data, a typical tropospheric lifetime of ClNO with respect to reaction with OH is calculated to be-36 days, too slow to compete with ClNO photolysis.

The Journal of Physical Chemistry, 1987

The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast f... more The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast flow discharge system using the reaction of hydrogen atoms with NOz as the source of OH. The decay of OH in excess ClNO at a total pressure of 1.05 0.05 Torr in He was followed by resonance fluorescence. at 309.5 nm at temperatures from 262 to 373 K in 2.4-cm-diameter flow tubes coated with boric acid, phosphoric acid, or halocarbon wax. Kinetic studies were also carried out in a 4.8-cm-diameter boric acid coated flow tube. While the rate of decay of OH increased both above and below room temperature in both boric acid coated flow tubes, more typical Arrhenius behavior was observed in the phosphoric acid and halocarbon wax coated tubes. The stable products observed by mass spectrometry from 276 to 353 K and from 0.2 to 0.8 Torr total pressure were HOCl, HONO, and CIz, which supports the existence of two reaction channels suggested in earlier work by Poulet and co-workers (1981): OH + ClNO-HOCl + NO (la), OH + ClNO-HONO + C1 (lb). Molecular CIz results from the reaction of Cl atoms with the excess ClNO present. The ratio of the products HOC1/ClZ did not change significantly with temperature or total pressure. All of these data taken together indicate that the temperature dependence observed in the boric acid coated flow tubes is due to an unusual surface reaction rather than intermediate complex formation in reaction 1 b. Taking only the data for which the surface reaction is believed to be negligible, the Arrhenius expression for the rate constant kl (= k l , + klb) for the reaction of OH with ClNO is kl = (1.5T; X exp[-(458 f 2 7) / a cm3 molecule-' s-l, with kl = (3.2 0.5) X cm3 molecule-' s-' at 298 K, where all errors are two standard deviations. From these kinetic data, a typical tropospheric lifetime of ClNO with respect to reaction with OH is calculated to be-36 days, too slow to compete with ClNO photolysis.

ACS Earth and Space Chemistry, 2021

The environmental fate of neonicotinoids (NNs) is a key regulatory issue due to their widespread ... more The environmental fate of neonicotinoids (NNs) is a key regulatory issue due to their widespread distribution, mobility, and role in honeybee colony collapse disorder. Here, we explore the potentia...

Communications Chemistry, 2020

Airborne particles have significant impacts on health, visibility, and climate. Here, an overview... more Airborne particles have significant impacts on health, visibility, and climate. Here, an overview of what is known about particle chemical composition is presented, along with open questions and challenges that are central to relating composition to life cycles and impacts. Airborne particles have been known for at least 800 years to negatively impact visibility and health. For example, Moses Ben Maimonides (1135-1204) described air in Cairo as "stagnant, turbid, thick, misty, and foggy", and attributed "dullness of understanding, failure of intelligence, and defect of memory" to "spoilage of the air". A recent estimate is that exposure to outdoor particulate matter (PM) currently leads to 3.3 million premature deaths per year worldwide, and this could double by the year 2050 1. It is known that these particles impact climate as well 2. The chemical composition of the particles is an important determinant of all of these atmospheric impacts. Hence, understanding the composition and processes affecting composition is critical for developing cost-effective control strategies. A first step is to distinguish "primary particles", those that are directly emitted from natural and anthropogenic sources such as sea spray, transportation, industry, forest fires, etc. from "secondary particles", those formed from chemical reactions of gaseous precursors in air. The latter include both inorganics such as sulfuric acid/sulfate from SO 2 oxidation and nitrate from NO x oxidation, as well as a host of volatile organics, which make up a major fraction of the particles around the world 3. Because there are thousands of potential organic precursors in air, and a number of different oxidation reactions involving O 3 and OH, Cl, and NO 3 radicals (Fig. 1), the organic component of particles becomes very complex 4. Further adding to the complexity of this secondary organic aerosol (SOA) are reactions in the condensed phase that can also form new products after the particle has formed 5. Composition, size, and phase A critical property of atmospheric particles is their size. Particles must grow from sub-nm seeds formed by the gas phase chemistry to~100 nm in order to scatter light efficiently. This reduces visibility and affects climate both directly through light scattering and indirectly through their impacts on clouds. This~100 nm size also efficiently reaches the alveolar region of the lung.

The Journal of Physical Chemistry, 1986

The temperature dependence of the reaction of OH with nitrosyl chloride, CINO, has been studied f... more The temperature dependence of the reaction of OH with nitrosyl chloride, CINO, has been studied from 263 to 373 K in a fast-flow discharge system. The decay of OH in the presence of excess CINO was followed by resonance fluorescence at 309.5 nm. The total pressure was 1.05 +/- 0.05 torr in He as the carrier gas. The rate constant increases both above and below room temperature suggesting the existence of two competing reaction paths, a direct abstraction reaction, HO + CINO ..-->.. HOCl + NO (1a) and one involving formation of an intermediate complex, HO + ClNO in equilibrium (HO x ClNO)* ..-->.. HONO + Cl (1b). This supports the interpretation of the room temperature product data of Poulet and co-workers. 13 references, 4 figures, 1 table.

Atmospheric Measurement Techniques, 2014

Ammonia and amines are common trace gases in the atmosphere and have a variety of both biogenic a... more Ammonia and amines are common trace gases in the atmosphere and have a variety of both biogenic and anthropogenic sources, with a major contribution coming from agricultural sites. In addition to their malodorous nature, both ammonia and amines have been shown to enhance particle formation from acids such as nitric, sulfuric and methanesulfonic acids, which has implications for visibility, human health and climate. A key component of quantifying the effects of these species on particle formation is accurate gasphase measurements in both laboratory and field studies. However, these species are notoriously difficult to measure as they are readily taken up on surfaces, including onto glass surfaces from aqueous solution as established in the present studies. We describe here a novel technique for measuring gas-phase ammonia and amines that involves uptake onto a weak cation exchange resin followed by extraction and analysis using ion chromatography. Two variants-one for parts per billion concentrations in air and the second with lower (parts per trillion) detection limits-are described. The latter involves the use of a custom-designed high-pressure cartridge to hold the resin for in-line extraction. These methods avoid the use of sampling lines, which can lead to significant inlet losses of these compounds. They also have the advantages of being relatively simple and inexpensive. The applicability of this technique to ambient air is demonstrated in measurements made near a cattle farm in Chino, CA.

Physical chemistry chemical physics : PCCP, Jan 8, 2017

Correction for 'New particle formation and growth from methanesulfonic acid, trimethylamine a... more Correction for 'New particle formation and growth from methanesulfonic acid, trimethylamine and water' by Haihan Chen et al., Phys. Chem. Chem. Phys., 2015, 17, 13699-13709.

Physical chemistry chemical physics : PCCP, Jan 8, 2017

Atmospheric particles adversely affect visibility, health, and climate, yet the kinetics and mech... more Atmospheric particles adversely affect visibility, health, and climate, yet the kinetics and mechanisms of particle formation and growth are poorly understood. Multiphase reactions between amines and dicarboxylic acids (diacids) have been suggested to contribute. In this study, the reactions of n-butylamine (BA) with solid C3-C8 diacids were studied at 296 ± 1 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. Uptake coefficients for amines on the diacids with known geometric surface areas were measured at initial amine concentrations from (3-50) × 10(11) cm(-3). Uptake coefficients ranged from 0.7 ± 0.1 (2σ) for malonic acid (C3) to <10(-6) for suberic acid (C8), show an odd-even carbon number effect, and decrease with increasing chain length within each series. Butylaminium salts formed from evaporation of aqueous solutions of BA with C3, C5 and C7 diacids (as well as C8) were viscous liquids, suggesting that ionic liquids (ILs) form on the surface during the ...

Atmospheric Measurement Techniques Discussions, 2016

The application of direct analysis in real time mass spectrometry (DART-MS), which is finding inc... more The application of direct analysis in real time mass spectrometry (DART-MS), which is finding increasing use in atmospheric chemistry, to two different laboratory model systems for airborne particles is investigated: (1) submicron C₃-C₇ dicarboxylic acid (diacid) particles reacted with gas phase trimethylamine (TMA) or butylamine (BA); (2) secondary organic aerosol (SOA) particles from the ozonolysis of α-cedrene. The diacid particles exhibit a clear odd-even pattern in their chemical reactivity toward TMA and BA, with the odd-carbon diacid particles being substantially more reactive than even ones. The ratio of base to acids in reacted particles, determined using known acid-base mixtures, was compared to that measured by high resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), which vaporizes the whole particle. Results show that DART-MS probes mainly surface layers, consistent with other studies on different systems. For ...

Environmental Science Technology, 2010

Physical Chemistry Chemical Physics, 2015

Water participates in the formation of initial clusters to enhance particle formation from methan... more Water participates in the formation of initial clusters to enhance particle formation from methanesulfonic acid and trimethylamine.

RSC Advances, 2012

Extractive electrospray ionization mass spectrometry (EESI-MS) has been shown, in other laborator... more Extractive electrospray ionization mass spectrometry (EESI-MS) has been shown, in other laboratories, to be a useful technique for the analysis of aerosols from a variety of sources. EESI-MS is applied here, for the first time, to the analysis of secondary organic aerosol (SOA) formed from the reaction of ozone and a-pinene. The results are compared to those obtained using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The SOA was generated in the laboratory and merged with electrospray droplets. The recovered ions were directed towards the inlet of a triple quadrupole mass spectrometer. Through the use of a denuder to remove gas phase compounds, the EESI-MS technique was found to be effective for measuring the major ozonolysis products either in particles alone or in a combination of vapor phase and particulate products. Due to its relatively simple setup and the avoidance of sample collection and work-up, EESI-MS shows promise as an excellent tool for the characterization of atmospherically relevant particles.

The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic com... more The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic compounds are O3, OH and nitrate radical (NO3). While O3 and OH-initiated oxidation occur during the day, NO3 radical-initiated oxidation is recognized to be a major contributor to the night-time chemistry of volatile organic compounds in the troposphere. Specifically, the reaction of biogenic hydrocarbons with NO3 is

A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formati... more A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formation and reactions of aerosols relevant to the troposphere has been constructed, modeled and experimentally tested. The total flow tube length is 7.3 m which includes a 1.2 m section used for mixing. The flow tube is equipped with ultraviolet lamps for photolysis. The diameter of

Proceedings of the National Academy of Sciences, 2012

Airborne particles play critical roles in air quality, health effects, visibility, and climate. S... more Airborne particles play critical roles in air quality, health effects, visibility, and climate. Secondary organic aerosols (SOA) formed from oxidation of organic gases such as α-pinene account for a significant portion of total airborne particle mass. Current atmospheric models typically incorporate the assumption that SOA mass is a liquid into which semivolatile organic compounds undergo instantaneous equilibrium partitioning to grow the particles into the size range important for light scattering and cloud condensation nuclei activity. We report studies of particles from the oxidation of α-pinene by ozone and NO 3 radicals at room temperature. SOA is primarily formed from low-volatility ozonolysis products, with a small contribution from higher volatility organic nitrates from the NO 3 reaction. Contrary to expectations, the particulate nitrate concentration is not consistent with equilibrium partitioning between the gas phase and a liquid particle. Rather the fraction of organic ...

Proceedings of the National Academy of Sciences, 2012

Airborne particles affect human health and significantly influence visibility and climate. A majo... more Airborne particles affect human health and significantly influence visibility and climate. A major fraction of these particles result from the reactions of gaseous precursors to generate low-volatility products such as sulfuric acid and high-molecular weight organics that nucleate to form new particles. Ammonia and, more recently, amines, both of which are ubiquitous in the environment, have also been recognized as important contributors. However, accurately predicting new particle formation in both laboratory systems and in air has been problematic. During the oxidation of organosulfur compounds, gas-phase methanesulfonic acid is formed simultaneously with sulfuric acid, and both are found in particles in coastal regions as well as inland. We show here that: ( i ) Amines form particles on reaction with methanesulfonic acid, ( ii ) water vapor is required, and ( iii ) particle formation can be quantitatively reproduced by a semiempirical kinetics model supported by insights from qua...

Physical Chemistry Chemical Physics, 2008

The photooxidation of 0.6-0.9 ppm a-pinene in the presence of a deliquesced thin film of NaNO 3 ,... more The photooxidation of 0.6-0.9 ppm a-pinene in the presence of a deliquesced thin film of NaNO 3 , and for comparison increasing concentrations of NO 2 , was studied in a 100 L Teflon s chamber at relative humidities from 72-88% and temperatures from 296-304 K. The loss of a-pinene and the formation of gaseous products were followed with time using proton transfer mass spectrometry. The yields of gas phase products were smaller in the NaNO 3 experiments than in NO 2 experiments. In addition, pinonic acid, pinic acid, trans-sobrerol and other unidentified products were detected in the extracts of the wall washings only for the NaNO 3 photolysis. These data indicate enhanced loss of a-pinene at the NaNO 3 thin film during photolysis. Supporting the experimental results are molecular dynamics simulations which predict that a-pinene has an affinity for the surface of the deliquesced nitrate thin film, enhancing the opportunity for oxidation of the impinging organic gas during the nitrate photolysis. This new mechanism of oxidation of organics may be partially responsible for the correlation between nitrate and the organic component of particles observed in many field studies, and may also contribute to the missing source of SOA needed to reconcile model predictions and field measurements. In addition, photolysis of nitrate on surfaces in the boundary layer may lead to oxidation of co-adsorbed organics.

The Journal of Chemical Physics, 1981

The production of significant concentrations of 0(' P) in the gas phase reaction of hydrogen atom... more The production of significant concentrations of 0(' P) in the gas phase reaction of hydrogen atoms with ozone in a fast flow discharge system at 1.1 ±0.1 Torr total pressure in Ar and at room temperature has been reported earlier. These yields were observed to be independent of the concentration of known deactivators of OHt (v = 9) such as 0, and CO,. We report here the results of detailed studies of the yields of 0(3p) and ground state OH(X '1T;),~O (OH) using resonance fluorescence under a wide variety of reaction conditions. It is shown that the highest yields of Oep), 27 ±2% of the calculated loss of 0 3 ,are observed when H is present in excess and the flow tube is coated with a halocarbon wax. The yields are substantially lower when 0 3 is present in excess and increases as [0 3 10 increases. In addition, in an excess of either reagent, the 0(' P) yields are lower when the walls of the flow tube are coated with boric acid, which is known to deactivate the vibrationally excited OHt produced in the initial reaction of H with 0 3 , Addition of NO decreased the yield of 0(3 PI, and increased the yield of OR. These results suggest that secondary reactions of OHt, likely with Hand 0 3 , are responsible for the production of O(,P), and that a second primary reaction channel, H + 03-+HO, + 0(' P) [Eq. (Ib)] accounts for :0; 2% of the net reaction. A subsequent direct search 28 for ground state H0 2 (ZA"), the second product in Reaction (lb), by laser magnetic resonance failed to detect this species and an upper lima

Environmental Science & Technology, 2011

Anthropogenic sources release into the troposphere a wide range of volatile organic compounds (VO... more Anthropogenic sources release into the troposphere a wide range of volatile organic compounds (VOCs) including aromatic hydrocarbons, whose major sources are believed to be combustion and the evaporation of fossil fuels. An important question is whether there are other sources of aromatics in air. We report here the formation of p-cymene [1-methyl-4-(1methylethyl) benzene, C 6 H 4 (CH 3)(C 3 H 7)] from the oxidation of R-pinene by OH, O 3 , and NO 3 at 1 atm in air and 298 K at low (<5%) and high (70%) relative humidities (RH). Loss of R-pinene and the generation of p-cymene were measured using GC-MS. The fractional yields of p-cymene relative to the loss of R-pinene, Δ [p-cymeme]/Δ [R-pinene], were measured to range from (1.6 (0.2) Â 10 À5 for the O 3 reaction to (3.0 (0.3) Â 10 À4 for the NO 3 reaction in the absence of added water vapor. The yields for the OH and O 3 reactions increased by a factor of 4À8 at 70% RH (uncertainties are (2s). The highest yields at 70% RH for the OH and O 3 reactions, ∼15 times higher than for dry conditions, were observed if the walls of the Teflon reaction chamber had been previously exposed to H 2 SO 4 formed from the OH oxidation of SO 2. Possible mechanisms of the conversion of R-pinene to p-cymene and the potential importance in the atmosphere are discussed. ' INTRODUCTION Volatile organic compounds (VOCs) are emitted into the atmosphere from both anthropogenic and biogenic sources. 1 Globally on a mass basis, emissions of VOCs from biogenic sources dominate, with ∼1150 Tg carbon per year 2 versus 140 Tg per year from anthropogenic sources. 3 The biogenic species include isoprene, monoterpenes, sesquiterpenes, and oxygenated hydrocarbons. 2,4 Among the monoterpenes, R-pinene is the most abundant. 2,5 In the troposphere, these compounds react with hydroxyl radicals (OH), ozone (O 3), and nitrate radicals (NO 3) 6 to form numerous oxidation products. Although biogenic sources of VOCs dominate over anthropogenic sources on a worldwide basis, this is not the case in urban areas. In cities such as Los Angeles, the nonmethane VOCs are typically 40À45% alkanes, 20% aromatic hydrocarbons, 10% alkenes, and 10À15% oxygenates in addition to some unidentified VOCs. 7 The major sources of monocyclic aromatic hydrocarbons, of which benzene, toluene, and the xylenes are the most abundant, include combustion and evaporation of fossil fuels. 8,9 Many of these aromatics and their oxidation products have adverse health effects and have been shown to be mutagenic. 10,11 In addition, aromatic hydrocarbons contribute significantly to photochemical air pollution and act as precursors to secondary organic aerosols (SOA). 12À14 Although there are clearly significant anthropogenic sources of aromatic hydrocarbons, they have also been recently associated with biogenic emissions. 15À18 For example, while p-cymene [1-methyl-4-(1-methylethyl) benzene, C 6 H 4 (CH 3)(C 3 H 7)] is released from motor vehicle exhaust, solvent evaporation, and industrial wastewater, 19,20 direct emissions from plants have also been reported. 2,21À24 Furthermore, the concentration of p-cymene was recently reported to increase as a function of altitude above a forest canopy that had significant emissions of R-pinene, 15 suggesting that it might be formed by atmospheric reactions. We report here studies showing that p-cymene can indeed be formed during the oxidation of R-pinene by OH, O 3 , or NO 3 in air. Possible mechanisms and atmospheric implications are discussed.

The Journal of Physical Chemistry, 1987

The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast f... more The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast flow discharge system using the reaction of hydrogen atoms with NOz as the source of OH. The decay of OH in excess ClNO at a total pressure of 1.05 0.05 Torr in He was followed by resonance fluorescence. at 309.5 nm at temperatures from 262 to 373 K in 2.4-cm-diameter flow tubes coated with boric acid, phosphoric acid, or halocarbon wax. Kinetic studies were also carried out in a 4.8-cm-diameter boric acid coated flow tube. While the rate of decay of OH increased both above and below room temperature in both boric acid coated flow tubes, more typical Arrhenius behavior was observed in the phosphoric acid and halocarbon wax coated tubes. The stable products observed by mass spectrometry from 276 to 353 K and from 0.2 to 0.8 Torr total pressure were HOCl, HONO, and CIz, which supports the existence of two reaction channels suggested in earlier work by Poulet and co-workers (1981): OH + ClNO-HOCl + NO (la), OH + ClNO-HONO + C1 (lb). Molecular CIz results from the reaction of Cl atoms with the excess ClNO present. The ratio of the products HOC1/ClZ did not change significantly with temperature or total pressure. All of these data taken together indicate that the temperature dependence observed in the boric acid coated flow tubes is due to an unusual surface reaction rather than intermediate complex formation in reaction 1 b. Taking only the data for which the surface reaction is believed to be negligible, the Arrhenius expression for the rate constant kl (= k l , + klb) for the reaction of OH with ClNO is kl = (1.5T; X exp[-(458 f 2 7) / a cm3 molecule-' s-l, with kl = (3.2 0.5) X cm3 molecule-' s-' at 298 K, where all errors are two standard deviations. From these kinetic data, a typical tropospheric lifetime of ClNO with respect to reaction with OH is calculated to be-36 days, too slow to compete with ClNO photolysis.

The Journal of Physical Chemistry, 1987

The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast f... more The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast flow discharge system using the reaction of hydrogen atoms with NOz as the source of OH. The decay of OH in excess ClNO at a total pressure of 1.05 0.05 Torr in He was followed by resonance fluorescence. at 309.5 nm at temperatures from 262 to 373 K in 2.4-cm-diameter flow tubes coated with boric acid, phosphoric acid, or halocarbon wax. Kinetic studies were also carried out in a 4.8-cm-diameter boric acid coated flow tube. While the rate of decay of OH increased both above and below room temperature in both boric acid coated flow tubes, more typical Arrhenius behavior was observed in the phosphoric acid and halocarbon wax coated tubes. The stable products observed by mass spectrometry from 276 to 353 K and from 0.2 to 0.8 Torr total pressure were HOCl, HONO, and CIz, which supports the existence of two reaction channels suggested in earlier work by Poulet and co-workers (1981): OH + ClNO-HOCl + NO (la), OH + ClNO-HONO + C1 (lb). Molecular CIz results from the reaction of Cl atoms with the excess ClNO present. The ratio of the products HOC1/ClZ did not change significantly with temperature or total pressure. All of these data taken together indicate that the temperature dependence observed in the boric acid coated flow tubes is due to an unusual surface reaction rather than intermediate complex formation in reaction 1 b. Taking only the data for which the surface reaction is believed to be negligible, the Arrhenius expression for the rate constant kl (= k l , + klb) for the reaction of OH with ClNO is kl = (1.5T; X exp[-(458 f 2 7) / a cm3 molecule-' s-l, with kl = (3.2 0.5) X cm3 molecule-' s-' at 298 K, where all errors are two standard deviations. From these kinetic data, a typical tropospheric lifetime of ClNO with respect to reaction with OH is calculated to be-36 days, too slow to compete with ClNO photolysis.

The Journal of Physical Chemistry, 1987

The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast f... more The kinetics and products of the gas-phase reaction of OH with ClNO have been studied in a fast flow discharge system using the reaction of hydrogen atoms with NOz as the source of OH. The decay of OH in excess ClNO at a total pressure of 1.05 0.05 Torr in He was followed by resonance fluorescence. at 309.5 nm at temperatures from 262 to 373 K in 2.4-cm-diameter flow tubes coated with boric acid, phosphoric acid, or halocarbon wax. Kinetic studies were also carried out in a 4.8-cm-diameter boric acid coated flow tube. While the rate of decay of OH increased both above and below room temperature in both boric acid coated flow tubes, more typical Arrhenius behavior was observed in the phosphoric acid and halocarbon wax coated tubes. The stable products observed by mass spectrometry from 276 to 353 K and from 0.2 to 0.8 Torr total pressure were HOCl, HONO, and CIz, which supports the existence of two reaction channels suggested in earlier work by Poulet and co-workers (1981): OH + ClNO-HOCl + NO (la), OH + ClNO-HONO + C1 (lb). Molecular CIz results from the reaction of Cl atoms with the excess ClNO present. The ratio of the products HOC1/ClZ did not change significantly with temperature or total pressure. All of these data taken together indicate that the temperature dependence observed in the boric acid coated flow tubes is due to an unusual surface reaction rather than intermediate complex formation in reaction 1 b. Taking only the data for which the surface reaction is believed to be negligible, the Arrhenius expression for the rate constant kl (= k l , + klb) for the reaction of OH with ClNO is kl = (1.5T; X exp[-(458 f 2 7) / a cm3 molecule-' s-l, with kl = (3.2 0.5) X cm3 molecule-' s-' at 298 K, where all errors are two standard deviations. From these kinetic data, a typical tropospheric lifetime of ClNO with respect to reaction with OH is calculated to be-36 days, too slow to compete with ClNO photolysis.

ACS Earth and Space Chemistry, 2021

The environmental fate of neonicotinoids (NNs) is a key regulatory issue due to their widespread ... more The environmental fate of neonicotinoids (NNs) is a key regulatory issue due to their widespread distribution, mobility, and role in honeybee colony collapse disorder. Here, we explore the potentia...

Communications Chemistry, 2020

Airborne particles have significant impacts on health, visibility, and climate. Here, an overview... more Airborne particles have significant impacts on health, visibility, and climate. Here, an overview of what is known about particle chemical composition is presented, along with open questions and challenges that are central to relating composition to life cycles and impacts. Airborne particles have been known for at least 800 years to negatively impact visibility and health. For example, Moses Ben Maimonides (1135-1204) described air in Cairo as "stagnant, turbid, thick, misty, and foggy", and attributed "dullness of understanding, failure of intelligence, and defect of memory" to "spoilage of the air". A recent estimate is that exposure to outdoor particulate matter (PM) currently leads to 3.3 million premature deaths per year worldwide, and this could double by the year 2050 1. It is known that these particles impact climate as well 2. The chemical composition of the particles is an important determinant of all of these atmospheric impacts. Hence, understanding the composition and processes affecting composition is critical for developing cost-effective control strategies. A first step is to distinguish "primary particles", those that are directly emitted from natural and anthropogenic sources such as sea spray, transportation, industry, forest fires, etc. from "secondary particles", those formed from chemical reactions of gaseous precursors in air. The latter include both inorganics such as sulfuric acid/sulfate from SO 2 oxidation and nitrate from NO x oxidation, as well as a host of volatile organics, which make up a major fraction of the particles around the world 3. Because there are thousands of potential organic precursors in air, and a number of different oxidation reactions involving O 3 and OH, Cl, and NO 3 radicals (Fig. 1), the organic component of particles becomes very complex 4. Further adding to the complexity of this secondary organic aerosol (SOA) are reactions in the condensed phase that can also form new products after the particle has formed 5. Composition, size, and phase A critical property of atmospheric particles is their size. Particles must grow from sub-nm seeds formed by the gas phase chemistry to~100 nm in order to scatter light efficiently. This reduces visibility and affects climate both directly through light scattering and indirectly through their impacts on clouds. This~100 nm size also efficiently reaches the alveolar region of the lung.

The Journal of Physical Chemistry, 1986

The temperature dependence of the reaction of OH with nitrosyl chloride, CINO, has been studied f... more The temperature dependence of the reaction of OH with nitrosyl chloride, CINO, has been studied from 263 to 373 K in a fast-flow discharge system. The decay of OH in the presence of excess CINO was followed by resonance fluorescence at 309.5 nm. The total pressure was 1.05 +/- 0.05 torr in He as the carrier gas. The rate constant increases both above and below room temperature suggesting the existence of two competing reaction paths, a direct abstraction reaction, HO + CINO ..-->.. HOCl + NO (1a) and one involving formation of an intermediate complex, HO + ClNO in equilibrium (HO x ClNO)* ..-->.. HONO + Cl (1b). This supports the interpretation of the room temperature product data of Poulet and co-workers. 13 references, 4 figures, 1 table.

Atmospheric Measurement Techniques, 2014

Ammonia and amines are common trace gases in the atmosphere and have a variety of both biogenic a... more Ammonia and amines are common trace gases in the atmosphere and have a variety of both biogenic and anthropogenic sources, with a major contribution coming from agricultural sites. In addition to their malodorous nature, both ammonia and amines have been shown to enhance particle formation from acids such as nitric, sulfuric and methanesulfonic acids, which has implications for visibility, human health and climate. A key component of quantifying the effects of these species on particle formation is accurate gasphase measurements in both laboratory and field studies. However, these species are notoriously difficult to measure as they are readily taken up on surfaces, including onto glass surfaces from aqueous solution as established in the present studies. We describe here a novel technique for measuring gas-phase ammonia and amines that involves uptake onto a weak cation exchange resin followed by extraction and analysis using ion chromatography. Two variants-one for parts per billion concentrations in air and the second with lower (parts per trillion) detection limits-are described. The latter involves the use of a custom-designed high-pressure cartridge to hold the resin for in-line extraction. These methods avoid the use of sampling lines, which can lead to significant inlet losses of these compounds. They also have the advantages of being relatively simple and inexpensive. The applicability of this technique to ambient air is demonstrated in measurements made near a cattle farm in Chino, CA.

Physical chemistry chemical physics : PCCP, Jan 8, 2017

Correction for 'New particle formation and growth from methanesulfonic acid, trimethylamine a... more Correction for 'New particle formation and growth from methanesulfonic acid, trimethylamine and water' by Haihan Chen et al., Phys. Chem. Chem. Phys., 2015, 17, 13699-13709.

Physical chemistry chemical physics : PCCP, Jan 8, 2017

Atmospheric particles adversely affect visibility, health, and climate, yet the kinetics and mech... more Atmospheric particles adversely affect visibility, health, and climate, yet the kinetics and mechanisms of particle formation and growth are poorly understood. Multiphase reactions between amines and dicarboxylic acids (diacids) have been suggested to contribute. In this study, the reactions of n-butylamine (BA) with solid C3-C8 diacids were studied at 296 ± 1 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. Uptake coefficients for amines on the diacids with known geometric surface areas were measured at initial amine concentrations from (3-50) × 10(11) cm(-3). Uptake coefficients ranged from 0.7 ± 0.1 (2σ) for malonic acid (C3) to <10(-6) for suberic acid (C8), show an odd-even carbon number effect, and decrease with increasing chain length within each series. Butylaminium salts formed from evaporation of aqueous solutions of BA with C3, C5 and C7 diacids (as well as C8) were viscous liquids, suggesting that ionic liquids (ILs) form on the surface during the ...

Atmospheric Measurement Techniques Discussions, 2016

The application of direct analysis in real time mass spectrometry (DART-MS), which is finding inc... more The application of direct analysis in real time mass spectrometry (DART-MS), which is finding increasing use in atmospheric chemistry, to two different laboratory model systems for airborne particles is investigated: (1) submicron C₃-C₇ dicarboxylic acid (diacid) particles reacted with gas phase trimethylamine (TMA) or butylamine (BA); (2) secondary organic aerosol (SOA) particles from the ozonolysis of α-cedrene. The diacid particles exhibit a clear odd-even pattern in their chemical reactivity toward TMA and BA, with the odd-carbon diacid particles being substantially more reactive than even ones. The ratio of base to acids in reacted particles, determined using known acid-base mixtures, was compared to that measured by high resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), which vaporizes the whole particle. Results show that DART-MS probes mainly surface layers, consistent with other studies on different systems. For ...

Environmental Science Technology, 2010

Physical Chemistry Chemical Physics, 2015

Water participates in the formation of initial clusters to enhance particle formation from methan... more Water participates in the formation of initial clusters to enhance particle formation from methanesulfonic acid and trimethylamine.

RSC Advances, 2012

Extractive electrospray ionization mass spectrometry (EESI-MS) has been shown, in other laborator... more Extractive electrospray ionization mass spectrometry (EESI-MS) has been shown, in other laboratories, to be a useful technique for the analysis of aerosols from a variety of sources. EESI-MS is applied here, for the first time, to the analysis of secondary organic aerosol (SOA) formed from the reaction of ozone and a-pinene. The results are compared to those obtained using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The SOA was generated in the laboratory and merged with electrospray droplets. The recovered ions were directed towards the inlet of a triple quadrupole mass spectrometer. Through the use of a denuder to remove gas phase compounds, the EESI-MS technique was found to be effective for measuring the major ozonolysis products either in particles alone or in a combination of vapor phase and particulate products. Due to its relatively simple setup and the avoidance of sample collection and work-up, EESI-MS shows promise as an excellent tool for the characterization of atmospherically relevant particles.

The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic com... more The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic compounds are O3, OH and nitrate radical (NO3). While O3 and OH-initiated oxidation occur during the day, NO3 radical-initiated oxidation is recognized to be a major contributor to the night-time chemistry of volatile organic compounds in the troposphere. Specifically, the reaction of biogenic hydrocarbons with NO3 is

A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formati... more A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formation and reactions of aerosols relevant to the troposphere has been constructed, modeled and experimentally tested. The total flow tube length is 7.3 m which includes a 1.2 m section used for mixing. The flow tube is equipped with ultraviolet lamps for photolysis. The diameter of

Proceedings of the National Academy of Sciences, 2012

Airborne particles play critical roles in air quality, health effects, visibility, and climate. S... more Airborne particles play critical roles in air quality, health effects, visibility, and climate. Secondary organic aerosols (SOA) formed from oxidation of organic gases such as α-pinene account for a significant portion of total airborne particle mass. Current atmospheric models typically incorporate the assumption that SOA mass is a liquid into which semivolatile organic compounds undergo instantaneous equilibrium partitioning to grow the particles into the size range important for light scattering and cloud condensation nuclei activity. We report studies of particles from the oxidation of α-pinene by ozone and NO 3 radicals at room temperature. SOA is primarily formed from low-volatility ozonolysis products, with a small contribution from higher volatility organic nitrates from the NO 3 reaction. Contrary to expectations, the particulate nitrate concentration is not consistent with equilibrium partitioning between the gas phase and a liquid particle. Rather the fraction of organic ...

Proceedings of the National Academy of Sciences, 2012

Airborne particles affect human health and significantly influence visibility and climate. A majo... more Airborne particles affect human health and significantly influence visibility and climate. A major fraction of these particles result from the reactions of gaseous precursors to generate low-volatility products such as sulfuric acid and high-molecular weight organics that nucleate to form new particles. Ammonia and, more recently, amines, both of which are ubiquitous in the environment, have also been recognized as important contributors. However, accurately predicting new particle formation in both laboratory systems and in air has been problematic. During the oxidation of organosulfur compounds, gas-phase methanesulfonic acid is formed simultaneously with sulfuric acid, and both are found in particles in coastal regions as well as inland. We show here that: ( i ) Amines form particles on reaction with methanesulfonic acid, ( ii ) water vapor is required, and ( iii ) particle formation can be quantitatively reproduced by a semiempirical kinetics model supported by insights from qua...

Physical Chemistry Chemical Physics, 2008

The photooxidation of 0.6-0.9 ppm a-pinene in the presence of a deliquesced thin film of NaNO 3 ,... more The photooxidation of 0.6-0.9 ppm a-pinene in the presence of a deliquesced thin film of NaNO 3 , and for comparison increasing concentrations of NO 2 , was studied in a 100 L Teflon s chamber at relative humidities from 72-88% and temperatures from 296-304 K. The loss of a-pinene and the formation of gaseous products were followed with time using proton transfer mass spectrometry. The yields of gas phase products were smaller in the NaNO 3 experiments than in NO 2 experiments. In addition, pinonic acid, pinic acid, trans-sobrerol and other unidentified products were detected in the extracts of the wall washings only for the NaNO 3 photolysis. These data indicate enhanced loss of a-pinene at the NaNO 3 thin film during photolysis. Supporting the experimental results are molecular dynamics simulations which predict that a-pinene has an affinity for the surface of the deliquesced nitrate thin film, enhancing the opportunity for oxidation of the impinging organic gas during the nitrate photolysis. This new mechanism of oxidation of organics may be partially responsible for the correlation between nitrate and the organic component of particles observed in many field studies, and may also contribute to the missing source of SOA needed to reconcile model predictions and field measurements. In addition, photolysis of nitrate on surfaces in the boundary layer may lead to oxidation of co-adsorbed organics.

The Journal of Chemical Physics, 1981

The production of significant concentrations of 0(' P) in the gas phase reaction of hydrogen atom... more The production of significant concentrations of 0(' P) in the gas phase reaction of hydrogen atoms with ozone in a fast flow discharge system at 1.1 ±0.1 Torr total pressure in Ar and at room temperature has been reported earlier. These yields were observed to be independent of the concentration of known deactivators of OHt (v = 9) such as 0, and CO,. We report here the results of detailed studies of the yields of 0(3p) and ground state OH(X '1T;),~O (OH) using resonance fluorescence under a wide variety of reaction conditions. It is shown that the highest yields of Oep), 27 ±2% of the calculated loss of 0 3 ,are observed when H is present in excess and the flow tube is coated with a halocarbon wax. The yields are substantially lower when 0 3 is present in excess and increases as [0 3 10 increases. In addition, in an excess of either reagent, the 0(' P) yields are lower when the walls of the flow tube are coated with boric acid, which is known to deactivate the vibrationally excited OHt produced in the initial reaction of H with 0 3 , Addition of NO decreased the yield of 0(3 PI, and increased the yield of OR. These results suggest that secondary reactions of OHt, likely with Hand 0 3 , are responsible for the production of O(,P), and that a second primary reaction channel, H + 03-+HO, + 0(' P) [Eq. (Ib)] accounts for :0; 2% of the net reaction. A subsequent direct search 28 for ground state H0 2 (ZA"), the second product in Reaction (lb), by laser magnetic resonance failed to detect this species and an upper lima

Environmental Science & Technology, 2011

Anthropogenic sources release into the troposphere a wide range of volatile organic compounds (VO... more Anthropogenic sources release into the troposphere a wide range of volatile organic compounds (VOCs) including aromatic hydrocarbons, whose major sources are believed to be combustion and the evaporation of fossil fuels. An important question is whether there are other sources of aromatics in air. We report here the formation of p-cymene [1-methyl-4-(1methylethyl) benzene, C 6 H 4 (CH 3)(C 3 H 7)] from the oxidation of R-pinene by OH, O 3 , and NO 3 at 1 atm in air and 298 K at low (<5%) and high (70%) relative humidities (RH). Loss of R-pinene and the generation of p-cymene were measured using GC-MS. The fractional yields of p-cymene relative to the loss of R-pinene, Δ [p-cymeme]/Δ [R-pinene], were measured to range from (1.6 (0.2) Â 10 À5 for the O 3 reaction to (3.0 (0.3) Â 10 À4 for the NO 3 reaction in the absence of added water vapor. The yields for the OH and O 3 reactions increased by a factor of 4À8 at 70% RH (uncertainties are (2s). The highest yields at 70% RH for the OH and O 3 reactions, ∼15 times higher than for dry conditions, were observed if the walls of the Teflon reaction chamber had been previously exposed to H 2 SO 4 formed from the OH oxidation of SO 2. Possible mechanisms of the conversion of R-pinene to p-cymene and the potential importance in the atmosphere are discussed. ' INTRODUCTION Volatile organic compounds (VOCs) are emitted into the atmosphere from both anthropogenic and biogenic sources. 1 Globally on a mass basis, emissions of VOCs from biogenic sources dominate, with ∼1150 Tg carbon per year 2 versus 140 Tg per year from anthropogenic sources. 3 The biogenic species include isoprene, monoterpenes, sesquiterpenes, and oxygenated hydrocarbons. 2,4 Among the monoterpenes, R-pinene is the most abundant. 2,5 In the troposphere, these compounds react with hydroxyl radicals (OH), ozone (O 3), and nitrate radicals (NO 3) 6 to form numerous oxidation products. Although biogenic sources of VOCs dominate over anthropogenic sources on a worldwide basis, this is not the case in urban areas. In cities such as Los Angeles, the nonmethane VOCs are typically 40À45% alkanes, 20% aromatic hydrocarbons, 10% alkenes, and 10À15% oxygenates in addition to some unidentified VOCs. 7 The major sources of monocyclic aromatic hydrocarbons, of which benzene, toluene, and the xylenes are the most abundant, include combustion and evaporation of fossil fuels. 8,9 Many of these aromatics and their oxidation products have adverse health effects and have been shown to be mutagenic. 10,11 In addition, aromatic hydrocarbons contribute significantly to photochemical air pollution and act as precursors to secondary organic aerosols (SOA). 12À14 Although there are clearly significant anthropogenic sources of aromatic hydrocarbons, they have also been recently associated with biogenic emissions. 15À18 For example, while p-cymene [1-methyl-4-(1-methylethyl) benzene, C 6 H 4 (CH 3)(C 3 H 7)] is released from motor vehicle exhaust, solvent evaporation, and industrial wastewater, 19,20 direct emissions from plants have also been reported. 2,21À24 Furthermore, the concentration of p-cymene was recently reported to increase as a function of altitude above a forest canopy that had significant emissions of R-pinene, 15 suggesting that it might be formed by atmospheric reactions. We report here studies showing that p-cymene can indeed be formed during the oxidation of R-pinene by OH, O 3 , or NO 3 in air. Possible mechanisms and atmospheric implications are discussed.