Publications (123)133.2 Total impact
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Article: Measurements of Trace Gases in the Inflow of South China Sea Background Air and Outflow of Regional Pollution at Tai O, Southern China
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ABSTRACT: We present a 16-month record of ozone (O3), carbon monoxide (CO), total reactive nitrogen (NOy), sulphur dioxide (SO2), methane (CH4), C2 – C8 non-methane hydrocarbons (NMHCs), C1 – C2 halocarbons, and dimethyl sulfide (DMS) measured at a southern China coastal site. The study aimed to establish/update seasonal profiles of chemically active trace gases and pollution tracers in subtropical Asia and to characterize the composition of the `background' atmosphere over the South China Sea (SCS) and of pollution outflow from the industrialized Pearl River Delta (PRD) region and southern China. Most of the measured trace gases of anthropogenic origin exhibited a winter maximum and a summer minimum, while O3 showed a maximum in autumn which is in contrast to the seasonal behavior of O3 in rural eastern China and in many mid-latitude remote locations in the western Pacific. The data were segregated into two groups representing the SCS background air and the outflow of regional continental pollution (PRD plus southern China), based on CO mixing ratios and meteorological conditions. NMHCs and halocarbon data were further analyzed to examine the relationships between their variability and atmospheric lifetime and to elucidate the extent of atmospheric processing in the sampled air parcels. The trace gas variability (S) versus lifetime (τ) relationship, defined by the power law, Slnx = Aτ− b, (where X is the trace gas mixing ratio) gives a fit parameter A of 1.39 and exponent b of 0.42 for SCS air, and A of 2.86 and b of 0.31 for the regional continental air masses. An examination of ln[n-butane]/ln[ethane] versus ln[propane]/ln[ethane] indicates that their relative abundance was dominated by mixing as opposed to photochemistry in both SCS and regional outflow air masses. The very low ratios of ethyne/CO, propane/ethane and toluene/benzene suggest that the SCS air mass has undergone intense atmospheric processing since these gases were released into the atmosphere. Compared to the results from other polluted rural sites and from urban areas, the large values of these species in the outflow of PRD/southern China suggest source(s) emitting higher levels of ethyne, benzene, and toluene, relative to light alkanes. These chemical characteristics could be unique indicators of anthropogenic emissions from southern China.Journal of Atmospheric Chemistry 04/2012; 52(3):295-317. · 0.99 Impact Factor -
Article: Airborne observations of methane emissions from rice cultivation in the Sacramento Valley of California
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ABSTRACT: Airborne measurements of methane (CH4) and carbon dioxide (CO2) were taken over the rice growing region of California's Sacramento Valley in the late spring of 2010 and 2011. From these and ancillary measurements, we show that CH4 mixing ratios were higher in the planetary boundary layer above the Sacramento Valley during the rice growing season than they were before it, which we attribute to emissions from rice paddies. We derive daytime emission fluxes of CH4 between 0.6 and 2.0% of the CO2 taken up by photosynthesis on a per carbon, or mole to mole, basis. We also use a mixing model to determine an average CH4/CO2 flux ratio of −0.6% for one day early in the growing season of 2010. We conclude the CH4/CO2 flux ratio estimates from a single rice field in a previous study are representative of rice fields in the Sacramento Valley. If generally true, the California Air Resources Board (CARB) greenhouse gas inventory emission rate of 2.7 × 1010 g CH4/yr is approximately three times lower than the range of probable CH4 emissions (7.8–9.3 × 1010 g CH4/yr) from rice cultivation derived in this study. We attribute this difference to decreased burning of the residual rice crop since 1991, which leads to an increase in CH4 emissions from rice paddies in succeeding years, but which is not accounted for in the CARB inventory.Journal of Geophysical Research 01/2012; 117(D24). · 3.02 Impact Factor -
Article: Ozone and alkyl nitrate formation from the Deepwater Horizon oil spill atmospheric emissions
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ABSTRACT: Ozone (O-3), alkyl nitrates (RONO2), and other photochemical products were formed in the atmosphere downwind from the Deepwater Horizon (DWH) oil spill by photochemical reactions of evaporating hydrocarbons with NOx (= NO + NO2) emissions from spill response activities. Reactive nitrogen species and volatile organic compounds (VOCs) were measured from an instrumented aircraft during daytime flights in the marine boundary layer downwind from the area of surfacing oil. A unique VOC mixture, where alkanes dominated the hydroxyl radical (OH) loss rate, was emitted into a clean marine environment, enabling a focused examination of O-3 and RONO2 formation processes. In the atmospheric plume from DWH, the OH loss rate, an indicator of potential O-3 formation, was large and dominated by alkanes with between 5 and 10 carbons per molecule (C-5-C-10). Observations showed that NOx was oxidized very rapidly with a 0.8 h lifetime, producing primarily C-6-C-10 RONO2 that accounted for 78% of the reactive nitrogen enhancements in the atmospheric plume 2.5 h downwind from DWH. Both observations and calculations of RONO2 and O-3 production rates show that alkane oxidation dominated O-3 formation chemistry in the plume. Rapid and nearly complete oxidation of NOx to RONO2 effectively terminated O-3 production, with O-3 formation yields of 6.0 +/- 0.5 ppbv O-3 per ppbv of NOx oxidized. VOC mixing ratios were in large excess of NOx, and additional NOx would have formed additional O-3 in this plume. Analysis of measurements of VOCs, O-3, and reactive nitrogen species and calculations of O-3 and RONO2 production rates demonstrate that NOx-VOC chemistry in the DWH plume is explained by known mechanisms.Journal of Geophysical Research-Atmospheres. 01/2012; 117. -
Article: Airborne and ground-based observations of a weekend effect in ozone, precursors, and oxidation products in the California South Coast Air Basin
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ABSTRACT: Airborne and ground-based measurements during the CalNex (California Research at the Nexus of Air Quality and Climate Change) field study in May/June 2010 show a weekend effect in ozone in the South Coast Air Basin (SoCAB) consistent with previous observations. The well-known and much-studied weekend ozone effect has been attributed to weekend reductions in nitrogen oxide (NOx = NO + NO2) emissions, which affect ozone levels via two processes: (1) reduced ozone loss by titration and (2) enhanced photochemical production of ozone due to an increased ratio of non-methane volatile organic compounds (VOCs) to NOx. In accord with previous assessments, the 2010 airborne and ground-based data show an average decrease in NOx of 46 +/- 11% and 34 +/- 4%, respectively, and an average increase in VOC/NOx ratio of 48 +/- 8% and 43 +/- 22%, respectively, on weekends. This work extends current understanding of the weekend ozone effect in the SoCAB by identifying its major causes and quantifying their relative importance from the available CalNex data. Increased weekend production of a VOC-NOx oxidation product, peroxyacetyl nitrate, compared to a radical termination product, nitric acid, indicates a significant contribution from increased photochemical production on weekends. Weekday-to-weekend differences in the products of NOx oxidation show 45 +/- 13% and 42 +/- 12% more extensive photochemical processing and, when compared with odd oxygen (O-x = O-3 + NO2), 51 +/- 14% and 22 +/- 17% greater ozone production efficiency on weekends in the airborne and ground-based data, respectively, indicating that both contribute to higher weekend ozone levels in the SoCAB.Journal of Geophysical Research-Atmospheres. 01/2012; 117. -
Article: Detailed comparisons of airborne formaldehyde measurements with box models during the 2006 INTEX-B campaign: potential evidence for unmeasured and multi-generation volatile organic carbon oxidation processing
Atmospheric Chemistry and Physics 03/2011; 11(3):9887-9957. · 4.88 Impact Factor -
Article: Organic aerosol formation downwind from the Deepwater Horizon oil spill.
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ABSTRACT: A large fraction of atmospheric aerosols are derived from organic compounds with various volatilities. A National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft made airborne measurements of the gaseous and aerosol composition of air over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico that occurred from April to August 2010. A narrow plume of hydrocarbons was observed downwind of DWH that is attributed to the evaporation of fresh oil on the sea surface. A much wider plume with high concentrations of organic aerosol (>25 micrograms per cubic meter) was attributed to the formation of secondary organic aerosol (SOA) from unmeasured, less volatile hydrocarbons that were emitted from a wider area around DWH. These observations provide direct and compelling evidence for the importance of formation of SOA from less volatile hydrocarbons.Science 03/2011; 331(6022):1295-9. · 31.20 Impact Factor -
Article: Transport of anthropogenic emissions during ARCTAS-A: a climatology and regional case studies
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ABSTRACT: The National Aeronautics and Space Administration (NASA) conducted the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission during 2008 as a part of the International Polar Year (IPY). The purpose of ARCTAS was to study the factors responsible for changes in the Arctic's atmospheric composition and climate. A major emphasis was to investigate Arctic haze, which is most pronounced during winter and early spring. This study focuses on the spring phase of ARCTAS (ARCTAS-A) that was based in Alaska during April 2008. Although anthropogenic emissions historically have been associated with Arctic haze, biomass burning dominated the ARCTAS-A period and has been the focus of many ARCTAS related studies. This study determines the common pathways for anthropogenic emissions during ARCTAS-A. Trajectories (air parcels) are released each day from three historically significant regions of anthropogenic emissions (Asia, North America, and Europe). These fifteen day forward trajectories are calculated using data from the Weather Research and Forecasting (WRF) model at 45 km horizontal resolution. The trajectories then are examined to determine: origins of emissions that reach the Arctic (defined as north of 70° N) within fifteen days, pathways of the emissions reaching the Arctic, Arctic entry locations, and altitudes at which the trajectories enter the Arctic. These results serve as regional "climatologies" for the ARCTAS-A period. Three cases during the ARCTAS-A period (one for each of the regions above) are examined using backward trajectories and chemical fingerprinting based on in situ data sampled from the NASA DC-8. The fingerprinting utilizes volatile organic compounds that represent pure anthropogenic tracers, Asian anthropogenic pollution, incomplete combustion, and natural gas emissions. We determine flight legs containing anthropogenic emissions and the pathways travelled by these emissions. Results show that the DC-8 sampled anthropogenic emissions from Asia, North America, and Europe during the spring phase of ARCTAS. The pathways travelled by these emissions agree with our derived "climatologies" and previous studies of Arctic transport. Meteorological analysis and trajectory calculations indicate that middle latitude cyclones and their associated warm conveyor belts play an important role in lofting the surface based emissions to their sampling altitude in all three cases.Atmospheric Chemistry and Physics Discussions. 01/2011; -
Article: Atmospheric emissions from the Deepwater Horizon spill constrain air-water partitioning, hydrocarbon fate, and leak rate
Geophysical Research Letters. 01/2011; 38:L07803. -
Article: Size-resolved aerosol emission factors and new particle formation/growth activity occurring in Mexico City during the MILAGRO 2006 Campaign
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ABSTRACT: Measurements of the aerosol size distribution from 11 nm to 2.5 microns were made in Mexico City in March, 2006, during the MILAGRO field campaign. Observations at the T0 research site could often be characterized by morning conditions with high particle mass concentrations, low mixing heights, and highly correlated particle number and CO2 concentrations, indicative that particle number is controlled by primary emissions. Average size-resolved and total number- and volume-based emission factors for combustion sources impacting T0 have been determined using a comparison of peak sizes in number and CO2 concentration peaks. The number emission and volume emission factors for particles from 11 nm to 494 nm are 1.23 × 1015 particles, and 7.54 × 1011 cubic microns per kg of carbon, respectively. Uncertainty on the number emission factor is approximately a factor of 1.5. The mode of the number emission factor was between 25 and 32 nm, while the mode of the volume factor was between 0.25 and 0.32 microns. These emission factors are reported as log normal model parameters and are compared with multiple emission factors from the literature. In Mexico City in the afternoon, the CO2 concentration drops during ventilation of the polluted layer, and the coupling between CO2 and particle number breaks down, especially during new particle formation events when particle number is no longer controlled by primary emissions. Using measurements of particle number and CO2 taken aboard the NASA DC-8, this emission factor was applied to the MCMA plume; the primary emission factor predicts less than 50% of the total particle number and the surplus particle count is not correlated with photochemical age. Primary particle volume and number in the size range 0.1–2 μm are similarly too low to predict the observed volume distribution. Contrary to the case for number, the apparent secondary volume increases with photochemical age. The size distribution of the apparent increase, with a mode at ~250 nm, is reported.Atmospheric Chemistry and Physics Discussions. 01/2011; -
Article: Boreal forest fire emissions in fresh Canadian smoke plumes: C 1-C 10 volatile organic compounds (VOCs), CO 2, CO, NO 2, NO, HCN and CH 3 CN
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ABSTRACT: Boreal regions comprise about 17 % of the global land area, and they both affect and are influenced by cli-mate change. To better understand boreal forest fire emis-sions and plume evolution, 947 whole air samples were col-lected aboard the NASA DC-8 research aircraft in summer 2008 as part of the ARCTAS-B field mission, and analyzed for 79 non-methane volatile organic compounds (NMVOCs) using gas chromatography. Together with simultaneous mea-surements of CO 2 , CO, CH 4 , CH 2 O, NO 2 , NO, HCN and CH 3 CN, these measurements represent the most comprehen-sive assessment of trace gas emissions from boreal forest fires to date. Based on 105 air samples collected in fresh Canadian smoke plumes, 57 of the 80 measured NMVOCs (including CH 2 O) were emitted from the fires, including 45 species that were quantified from boreal forest fires for the first time. After CO 2 , CO and CH 4 , the largest emis-sion factors (EFs) for individual species were formalde-hyde (2.1 ± 0.2 g kg −1), followed by methanol, NO 2 , HCN, ethene, α-pinene, β-pinene, ethane, benzene, propene, ace-tone and CH 3 CN. Globally, we estimate that boreal forest fires release 2.4 ± 0.6 Tg C yr −1 in the form of NMVOCs, with approximately 41 % of the carbon released as C 1 -C 2 NMVOCs and 21 % as pinenes. These are the first reported field measurements of monoterpene emissions from boreal Correspondence to: I. J. Simpson (isimpson@uci.edu) forest fires, and we speculate that the pinenes, which are rel-atively heavy molecules, were detected in the fire plumes as the result of distillation of stored terpenes as the vege-tation is heated. Their inclusion in smoke chemistry mod-els is expected to improve model predictions of secondary organic aerosol (SOA) formation. The fire-averaged EF of dichloromethane or CH 2 Cl 2 , (6.9 ± 8.6) × 10 −4 g kg −1 , was not significantly different from zero and supports recent findings that its global biomass burning source appears to have been overestimated. Similarly, we found no evidence for emissions of chloroform (CHCl 3) or methyl chloroform (CH 3 CCl 3) from boreal forest fires. The speciated hydro-carbon measurements presented here show the importance of carbon released by short-chain NMVOCs, the strong con-tribution of pinene emissions from boreal forest fires, and the wide range of compound classes in the most abundantly emitted NMVOCs, all of which can be used to improve biomass burning inventories in local/global models and re-duce uncertainties in model estimates of trace gas emissions and their impact on the atmosphere.Atmos. Chem. Phys. – Published in Atmos. Chem. Phys. Discuss. 01/2011; 11:6445-6463. -
Article: Emissions of black carbon, organic, and inorganic aerosols from biomass burning in North America and Asia in 2008
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ABSTRACT: 1] Reliable assessment of the impact of aerosols emitted from boreal forest fires on the Arctic climate necessitates improved understanding of emissions and the microphysical properties of carbonaceous (black carbon (BC) and organic aerosols (OA)) and inorganic aerosols. The size distributions of BC were measured by an SP2 based on the laser‐induced incandescence technique on board the DC‐8 aircraft during the NASA ARCTAS campaign. Aircraft sampling was made in fresh plumes strongly impacted by wildfires in North America (Canada and California) in summer 2008 and in those transported from Asia (Siberia in Russia and Kazakhstan) in spring 2008. We extracted biomass burning plumes using particle and tracer (CO, CH 3 CN, and CH 2 Cl 2) data. OA constituted the dominant fraction of aerosols mass in the submicron range. The large majority of the emitted particles did not contain BC. We related the combustion phase of the fire as represented by the modified combustion efficiency (MCE) to the emission ratios between BC and other species. In particular, we derived the average emission ratios of BC/CO = 2.3 ± 2.2 and 8.5 ± 5.4 ng m −3 /ppbv for BB in North America and Asia, respectively. The difference in the BC/CO emission ratios is likely due to the difference in MCE. The count median diameters and geometric standard deviations of the lognormal size distribution of BC in the BB plumes were 136–141 nm and 1.32–1.36, respectively, and depended little on MCE. These BC particles were thickly coated, with shell/core ratios of 1.3–1.6. These parameters can be used directly for improving model estimates of the impact of BB in the Arctic.J. Geophys. Res. 01/2011; 116. -
Article: Detailed comparisons of airborne formaldehyde measurements with box models during the 2006 INTEX-B and MILAGRO campaigns: potential evidence for significant impacts of unmeasured and multi-generation volatile organic carbon compounds
Atmospheric Chemistry and Physics 01/2011; 11(22):11867-11894. -
Article: The glyoxal budget and its contribution to organic aerosol for Los Angeles, California, during CalNex 2010
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ABSTRACT: Recent laboratory and field studies have indicated that glyoxal is a potentially large contributor to secondary organic aerosol mass. We present in situ glyoxal measurements acquired with a recently developed, high sensitivity spectroscopic instrument during the CalNex 2010 field campaign in Pasadena, California. We use three methods to quantify the production and loss of glyoxal in Los Angeles and its contribution to organic aerosol. First, we calculate the difference between steady state sources and sinks of glyoxal at the Pasadena site, assuming that the remainder is available for aerosol uptake. Second, we use the Master Chemical Mechanism to construct a two-dimensional model for gas-phase glyoxal chemistry in Los Angeles, assuming that the difference between the modeled and measured glyoxal concentration is available for aerosol uptake. Third, we examine the nighttime loss of glyoxal in the absence of its photochemical sources and sinks. Using these methods we constrain the glyoxal loss to aerosol to be 0-5 x 10(-5) s(-1) during clear days and (1 +/- 0.3) x 10(-5) s(-1) at night. Between 07:00-15:00 local time, the diurnally averaged secondary organic aerosol mass increases from 3.2 mu g m(-3) to a maximum of 8.8 mu g m(-3). The constraints on the glyoxal budget from this analysis indicate that it contributes 0-0.2 mu g m(-3) or 0-4% of the secondary organic aerosol mass.Journal of Geophysical Research-Atmospheres. 01/2011; 116. -
Article: Atmospheric chemistry results from the ANTCI 2005 Antarctic plateau airborne study
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ABSTRACT: One of the major goals of the 2005 Antarctic Tropospheric Chemistry Investigation (ANTCI) was to bridge the information gap between current knowledge of South Pole (SP) chemistry and that of the plateau. The former has been extensively studied, but its geographical position on the edge of the plateau makes extrapolating these findings across the plateau problematic. The airborne observations reported here demonstrate that, as at SP, elevated levels of nitric oxide (NO) are a common summertime feature of the plateau. As in earlier studies, planetary boundary layer (PBL) variations were a contributing factor leading to NO fluctuations. Thus, extensive use was made of in situ measurements and models to characterize PBL depths along each flight path and over broader areas of the plateau. Consistent with earlier SP studies that revealed photolysis of nitrate in surface snow as the source of NO(x), large vertical gradients in NO were observed over most plateau areas sampled. Similar gradients were also found for the nitrogen species HNO(3) and HO(2)NO(2) and for O(3). Thus, a common meteorological-chemical feature found was shallow PBLs associated with nitrogen species concentrations that exceeded free tropospheric levels. Collectively, these new results greatly extend the geographical sampling footprint defined by earlier SP studies. In particular, they suggest that previous assessments of the plateau as simply a chemical depository need updating. Although the evidence supporting this position comes in many forms, the fact that net photochemical production of ozone occurs during summer months over extensive areas of the plateau is pivotal.Journal of Geophysical Research-Atmospheres. 01/2010; 115. -
Article: An ozone episode in the Pearl River Delta: Field observation and model simulation
Journal of Geophysical Research-Atmospheres. 01/2010; 115. -
Article: The production and persistence of ΣceRONO2 in the Mexico City plume
Atmospheric Chemistry and Physics. 01/2010; 10(15):7215-7229. -
Article: Characterization of trace gases measured over Alberta oil sands mining operations: 76 speciated C<sub>2</sub>–C<sub>10</sub> volatile organic compounds (VOCs), CO<sub>2</sub>, CH<sub>4</sub>, CO, NO, NO<sub>2</sub>, NO<sub>y</sub>, O<sub>3</sub> and SO<sub>2</sub>
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ABSTRACT: Oil sands comprise 30% of the world's oil reserves and the crude oil reserves in Canada's oil sands deposits are second only to Saudi Arabia. The extraction and processing of oil sands is much more challenging than for light sweet crude oils because of the high viscosity of the bitumen contained within the oil sands and because the bitumen is mixed with sand and contains chemical impurities such as sulphur. Despite these challenges, the importance of oil sands is increasing in the energy market. To our best knowledge this is the first peer-reviewed study to characterize volatile organic compounds (VOCs) emitted from Alberta's oil sands mining sites. We present high-precision gas chromatography measurements of 76 speciated C2–C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes, aromatics, monoterpenes, oxygenated hydrocarbons, halocarbons and sulphur compounds) in 17 boundary layer air samples collected over surface mining operations in northeast Alberta on 10 July 2008, using the NASA DC-8 airborne laboratory as a research platform. In addition to the VOCs, we present simultaneous measurements of CO2, CH4, CO, NO, NO2, NOy, O3 and SO2, which were measured in situ aboard the DC-8. Carbon dioxide, CH4, CO, NO, NO2, NOy, SO2 and 53 VOCs (e.g., non-methane hydrocarbons, halocarbons, sulphur species) showed clear statistical enhancements (1.1–397×) over the oil sands compared to local background values and, with the exception of CO, were greater over the oil sands than at any other time during the flight. Twenty halocarbons (e.g., CFCs, HFCs, halons, brominated species) either were not enhanced or were minimally enhanced (<10%) over the oil sands. Ozone levels remained low because of titration by NO, and three VOCs (propyne, furan, MTBE) remained below their 3 pptv detection limit throughout the flight. Based on their correlations with one another, the compounds emitted by the oil sands industry fell into two groups: (1) evaporative emissions from the oil sands and its products and/or from the diluent used to lower the viscosity of the extracted bitumen (i.e., C4–C9 alkanes, C5–C6 cycloalkanes, C6–C8 aromatics), together with CO; and (2) emissions associated with the mining effort, such as upgraders (i.e., CO2, CO, CH4, NO, NO2, NOy, SO2, C2–C4 alkanes, C2–C4 alkenes, C9 aromatics, short-lived solvents such as C2Cl4 and C2HCl3, and longer-lived species such as HCFC-22 and HCFC-142b). Prominent in the second group, SO2 and NO were remarkably enhanced over the oil sands, with maximum mixing ratios of 38.7 ppbv and 5.0 ppbv, or 383× and 319× the local background, respectively. These SO2 levels are comparable to maximum values measured in heavily polluted megacities such as Mexico City and are attributed to coke combustion. By contrast, relatively poor correlations between CH4, ethane and propane suggest low levels of natural gas leakage despite its heavy use at the surface mining sites. Instead the elevated CH4 levels are attributed to methanogenic tailings pond emissions. In addition to the emission of many trace gases, the natural drawdown of OCS by vegetation was absent above the surface mining operations, presumably because of the widespread land disturbance. Unexpectedly, the mixing ratios of α-pinene and β-pinene were much greater over the oil sands (up to 217 pptv and 610 pptv, respectively) than over vegetation in the background boundary layer (20±7 pptv and 84±24 pptv, respectively), and the pinenes correlated well with several industrial tracers that were elevated in the oil sands plumes. Because so few independent measurements from the oil sands mining industry exist, this study provides an important initial characterization of trace gas emissions from oil sands surface mining operations.Atmospheric Chemistry and Physics. 01/2010; -
Article: The production and persistence of ΣRONO<sub>2</sub> in the Mexico City plume
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ABSTRACT: Alkyl and multifunctional nitrates (RONO<sub>2</sub>, ΣANs) have been observed to be a significant fraction of NO<sub>y</sub> in a number of different chemical regimes. Their formation is an important free radical chain termination step ending production of ozone and possibly affecting formation of secondary organic aerosol. ΣANs also represent a potentially large, unmeasured contribution to OH reactivity and are a major pathway for the removal of nitrogen oxides from the atmosphere. Numerous studies have investigated the role of nitrate formation from biogenic compounds and in the remote atmosphere. Less attention has been paid to the role ΣANs may play in the complex mixtures of hydrocarbons typical of urban settings. Measurements of total alkyl and multifunctional nitrates, NO<sub>2</sub>, total peroxy nitrates (ΣPNs), HNO<sub>3</sub> and a representative suite of hydrocarbons were obtained from the NASA DC-8 aircraft during spring of 2006 in and around Mexico City and the Gulf of Mexico. ΣANs were observed to be 10–20% of NO<sub>y</sub> in the Mexico City plume and to increase in importance with increased photochemical age. We describe three conclusions: (1) Correlations of ΣANs with odd-oxygen (O<sub>x</sub>) indicate a stronger role for ΣANs in the photochemistry of Mexico City than is expected based on currently accepted photochemical mechanisms, (2) ΣAN formation suppresses peak ozone production rates by as much as 40% in the near-field of Mexico City and (3) ΣANs play a significant role in the export of NO<sub>y</sub> from Mexico City to the Gulf Region.Atmospheric Chemistry and Physics. 01/2010; -
Article: Impact of organic nitrates on urban ozone production
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ABSTRACT: Urban O3 is produced by photochemical chain reactions that amplify background O3 in mixtures of gaseous nitrogen oxides (NOx) and organic molecules. Current thinking treats NOx and organics as independent variables that limit O3 production depending on the NOx to organic ratio; in this paradigm, reducing organics either has no effect or reduces O3. We describe a theoretical counterexample where NOx and organics are strongly coupled and reducing organics increases O3 production, and illustrate the example with observations from Mexico City. This effect arises from chain termination in the HOx and NOx cycles via organic nitrate production. We show that emission reductions that inadvertently reduce organic nitrate production rates will be counterproductive without concurrent reductions in NOx or other organics.Atmospheric Chemistry and Physics Discussions. 01/2010; -
Article: HFC-152a and HFC-134a emission estimates and characterization of CFCs, CFC replacements, and other halogenated solvents measured during the 2008 ARCTAS campaign (CARB phase) over the South Coast Air Basin of California
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ABSTRACT: This work presents results from the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) study. Whole air samples were obtained on board research flights that flew over California during June 2008 and analyzed for selected volatile organic compounds, including several halogenated species. Samples collected over the South Coast Air Basin of California (SoCAB), which includes much of Los Angeles (LA) County, were compared with samples from inflow air masses over the Pacific Ocean. The levels of many halocarbon species were enhanced significantly over the SoCAB, including compounds regulated by the Montreal Protocol and subsequent amendments (e.g., enhancements of 13 pptv and 11 pptv for CFC-11 and CFC-12, respectively). Emissions estimates of HFC-152a (0.98±0.05 Gg) and HFC-134a (1.40±0.11 Gg) in LA County for 2008 were obtained using the observed HFC:CO enhancement ratio. The emission rates were extrapolated to the SoCAB (1.48±0.07 Gg for HFC-152a and 2.12±0.17 Gg for HFC-134a) and US (30.1±1.5 Gg for HFC-152a and 43.0±3.4 Gg for HFC-134a) using population data. In addition, emission rates of the two HFCs in LA County and SoCAB also were calculated by a second method that utilizes air quality modeling. Estimates obtained using both methods agree well.Atmospheric Chemistry and Physics Discussions. 01/2010;
Top co-authors
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Institutions
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2–2012
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University of California, Irvine
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Irvine, CA, USA
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2009
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CSU Mentor
Long Beach, CA, USA
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2006
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University of Miami
Coral Gables, FL, USA
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2001
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Drexel University
Philadelphia, PA, USA
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