Publications

Trace gas concentrations and atmospheric state parameters were measured aboard the NOAA King Air research aircraft during flights on August 16, 1988, along the Appalachian Mountains from central Pennsylvania to northern Georgia. Stepwise profiles were flown over five surface sites where measurements of certain atmospheric parameters were being made. A stationary cold front lying across southern Virginia effectively divided the area into two weather regimes; to the north of the frontal zone the air was slightly cooler and much drier than that to the south. Considerable convective activity developed from early to midafternoon along and south of the front. The comparison between the aircraft and ground sites included measurements of the primary pollutants SO 2 and several hydrocarbons, NO y , the secondary pollutants H 2 O 2 and O 3 , and meteorological parameters. Continuity between the aircraft and surface meteorological and trace gas measurements was consistent at the northernmost site, which is situated in a relatively level valley. The agreement was poorer at the other four ground sites, which are located on or near mountaintops. Most of the meteorological and trace gas measurements, other than those made at Scotia, were found to differ by substantial margins, often by more than 10 times the resolution of the instruments. However, within a few hours after the flights, the surface measurements, particularly those of H 2 O 2 and O 3 , achieved values comparable to those measured with the aircraft, thus suggesting that air sampled at the canopy level did not mix readily with the bulk of the boundary layer.

Abstract Methyl ethyl ketone (MEK) is a relatively abundant but understudied oxygenated volatile organic compound that can serve as a source of both HO x and PAN when photooxidized. We use aircraft observations of MEK from the remote marine troposphere to show that the ocean serves as a source of MEK to the atmosphere during both meteorological winter and summer. There is pronounced seasonality in the MEK profiles in the extratropical troposphere, with higher MEK mixing ratios observed in summer than in winter. MEK in clean air over the remote oceans correlates with both acetone and acetaldehyde, whose primary sources in the ocean water are the photooxidation of organic material. We show that even a small (>1 nM) concentration of MEK in surface waters is sufficient to allow the ocean to be a net source of MEK to the atmosphere over ocean basins across multiple seasons.

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.

Increasing atmospheric mixing ratios of CO 2 have already lowered surface ocean pH by 0.1 units compared to preindustrial values and pH is expected to decrease an additional 0.3 units by the end of this century. Pronounced physiological changes in some phytoplankton have been observed during previous CO 2 perturbation experiments. Marine microorganisms are known to consume and produce climate‐relevant organic gases. Concentrations of (CH 3 ) 2 S (DMS) and CH 2 ClI were quantified during the Third Pelagic Ecosystem CO 2 Enrichment Study. Positive feedbacks were observed between control mesocosms and those simulating future CO 2 . Dimethyl sulfide was 26% (±10%) greater than the controls in the 2x ambient CO 2 treatments, and 18% (±10%) higher in the 3xCO 2 mesocosms. For CH 2 ClI the 2xCO 2 treatments were 46% (±4%) greater than the controls and the 3xCO 2 mesocosms were 131% (±11%) higher. These processes may help contribute to the homeostasis of the planet.

This study examines the influence of photochemical processes on ozone distributions in the western North Pacific. The analysis is based on data generated during NASA's western Pacific Exploratory Mission (PEM‐West A) during the fall of 1991. Ozone trends were best described in terms of two geographical domains: the western North Pacific rim (WNPR) and the western tropical North Pacific (WTNP). For both geographical regions, ozone photochemical destruction, D(O 3 ), decreased more rapidly with altitude than did photochemical formation, F(O 3 ). Thus the ozone tendency, P(O 3 ), was typically found to be negative for z < 6 km and positive for z > 6–8 km. For nearly all altitudes and latitudes, observed nonmethane hydrocarbon (NMHC) levels were shown to be of minor importance as ozone precursor species. Air parcel types producing the largest positive values of P(O 3 ) included fresh continental boundary layer (BL) air and high‐altitude (z > 7 km) parcels influenced by deep convection/lightning. Significant negative P(O 3 ) values were found when encountering clean marine BL air or relatively clean lower free‐tropospheric air. Photochemical destruction and formation fluxes for the Pacific rim region were found to exceed average values cited for marine dry deposition and stratospheric injection in the northern hemisphere by nearly a factor of 6. This region was also found to be in near balance with respect to column‐integrated O 3 photochemical production and destruction. By contrast, for the tropical regime column‐integrated O 3 showed photochemical destruction exceeding production by nearly 80%. Both transport of O 3 rich midlatitude air into the tropics as well as very high‐altitude (10–17 km) photochemical O 3 production were proposed as possible additional sources that might explain this estimated deficit. Results from this study further suggest that during the fall time period, deep convection over Asia and Malaysia/Indonesia provided a significant source of high‐altitude NO x to the western Pacific. Given that the high‐altitude NO x lifetime is estimated at between 3 and 9 days, one would predict that this source added significantly to high altitude photochemical O 3 formation over large areas of the western Pacific. When viewed in terms of strong seasonal westerly flow, its influence would potentially span a large part of the Pacific.

Abstract. The Sulfur Transport and dEposition Model (STEM) is applied to the analysis of observations obtained during the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B), conducted over the eastern Pacific Ocean during spring 2006. Predicted trace gas and aerosol distributions over the Pacific are presented and discussed in terms of transport and source region contributions. Trace species distributions show a strong west (high) to east (low) gradient, with the bulk of the pollutant transport over the central Pacific occurring between ~20° N and 50° N in the 2–6 km altitude range. These distributions are evaluated in the eastern Pacific by comparison with the NASA DC-8 and NSF/NCAR C-130 airborne measurements along with observations from the Mt. Bachelor (MBO) surface site. Thirty different meteorological, trace gas and aerosol parameters are compared. In general the meteorological fields are better predicted than gas phase species, which in turn are better predicted than aerosol quantities. PAN is found to be significantly overpredicted over the eastern Pacific, which is attributed to uncertainties in the chemical reaction mechanisms used in current atmospheric chemistry models in general and to the specifically high PAN production in the SAPRC-99 mechanism used in the regional model. A systematic underprediction of the elevated sulfate layer in the eastern Pacific observed by the C-130 is another issue that is identified and discussed. Results from source region tagged CO simulations are used to estimate how the different source regions around the Pacific contribute to the trace gas species distributions. During this period the largest contributions were from China and from fires in South/Southeast and North Asia. For the C-130 flights, which operated off the coast of the Northwest US, the regional CO contributions range as follows: China (35%), South/Southeast Asia fires (35%), North America anthropogenic (20%), and North Asia fires (10%). The transport of pollution into the western US is studied at MBO and a variety of events with elevated Asian dust, and periods with contributions from China and fires from both Asia and North America are discussed. The role of heterogeneous chemistry on the composition over the eastern Pacific is also studied. The impacts of heterogeneous reactions at specific times can be significant, increasing sulfate and nitrate aerosol production and reducing gas phase nitric acid levels appreciably (~50%).

The goal of the study is to model the elimination kinetics of Hydrofluoroalkane (HFA‐134a) in the exhaled breath following a typical single asthma inhaler administration. HFA‐134a is the most commonly used aerosol propellant in metered dose inhalers. We previously demonstrated that our technical capabilities allow us to measure breath HFA‐134a levels at 24 to 48 hours post asthma inhaler administration, and thus breath HFA‐134a is a promising biomarker for identifying asthma inhaler compliance ( Clinical and Translational Science 2015). Exhaled breath gases were collected in evacuated electro‐polished stainless steel canisters from healthy participants at baseline and at 5 min, 7 min, 10 min, 15 min, 30 min, 1hr, 2hr, 3hr, 4hr, 6hr, 8hr, 12hr. 24hr, 36hr, and 48hr ‐post inhaled corticosteroids administration (Flovent HFA, Glaxo Smith Kline). The corresponding ambient HFA‐134a levels were also measured. HFA‐134a levels in the breath and ambient air samples were quantified using gas chromatography with a quadrupole mass spectrometer detector. The Institutional Review Board at the University of California, Irvine approved the study, and informed consent was obtained from the participants. HFA elimination in the breath followed a three‐exponential pharmacokinetic model. The estimated time constants (mean (SD)) for the three components were 5.5 (0.5) minutes, 62.4 (11.1) minutes, and 664 (140) minutes, with an overall mean retention time (MRT) of 71.8 (40.4) minutes. The shortest and longest half‐life components comprised 66 (17) % and 9 (7) % of the total area under the curve, respectively. Breath carbon dioxide (CO 2 ) levels were also monitored as a reference breath gas to ensure that the gas sampled was alveolar gas. The mean (SD) CO 2 level was 4.7 (0.6) % of all breath samples. This study demonstrates that the breath HFA‐134a elimination in healthy control humans can be described by a 3 rd order exponential equation. In earlier studies, we modeled bicarbonate distribution kinetics and found similar time constants (2.2 min, 11.9 min, and 83.3 min; MRT 65 min.; Barstow et al. Am. J. Physiol. 259: R163, 1990 ). We speculate that the first two time constants reflect compartmental kinetics with the lung and circulation while the slowest primarily reflects distribution to body tissues. The kinetics for HFA‐134a appear to be slower than for bicarbonate. The calculated HFA‐134a elimination parameters (i.e., rate constants or corresponding half‐lives) may be useful in conjunction with breath HFA‐134a levels for accessing asthma inhaler medication compliance and further to understand physiological complexity of the lungs that affect HFA‐134a elimination. Support or Funding Information This work was supported by NIH grants: Translational Pilot Research Award (subaward of UL1 TR000153) and Program Project Grant P01HD048721

A field campaign was carried out in September–November 2010 near the summit of Mt. Tai Mo Shan in Hong Kong. Isoprene, methyl vinyl ketone (MVK) and methacrolein (MAC) were measured. The average isoprene mixing ratio was 109 pptv, and the average MAC and MVK levels were 68 pptv and 164 pptv, respectively. The average daytime levels of isoprene (149 ± 20 pptv, average ± 95% confidence interval, p < 0.01), MAC (70 ± 9 pptv, p < 0.01) and MVK (169 ± 22 pptv, p < 0.1) were significantly higher than the average nighttime values (20 ± 5 pptv, 49 ± 8 pptv and 139 ± 25 pptv, respectively). The relationship between MVK and MAC indicated that nearby isoprene oxidation dominated their daytime abundances, while NO 3 chemistry and regional transport of anthropogenic sources from inland Pearl River Delta region could explain the higher MVK to MAC ratios at night. Correlation analysis of [MVK]/[isoprene] versus [MAC]/[isoprene] found that the isoprene photochemical ages were between 10 and 64 min. Regression analysis of total O 3 (O 3 + NO 2 ) versus MVK resulted in an estimated contribution of isoprene oxidation to ozone production of 12.5%, consistent with the simulated contribution of 10‐11% by an observation‐based model.

An important objective of the Pacific Exploratory Mission‐West A (PEM‐West A) was the chemical characterization of the outflow of tropospheric trace gases and aerosol particles from the Asian continent over the western Pacific Ocean. This paper summarizes the chemistry of this outflow during the period September – October 1991. The vertical distributions of CO, C 2 H 6 , and NO x showed regions of outflow at altitudes below 2 km and from 8 to 12 km. Mixing ratios of CO were ≈130 parts per billion by volume (ppbv), ≈1000 parts per trillion by volume (pptv) for C 2 H 6 , and ≈100 pptv for NO x in both of these regions. Direct outflow of Asian industrial materials was clearly evident at altitudes below 2 km, where halocarbon tracer compounds such as CH 3 CCl 3 and C 2 Cl 4 were enhanced about threefold compared to aged Pacific air. The source attribution of species outflowing from Asia to the Pacific at 8–12 km altitude was not straightforward. Above 10 km altitude there were substantial enhancements of NO y , O 3 , CO, CH 4 SO 2 , C 2 H 6 , C 3 H 8 , C 2 H 2 , and aerosol 210 Pb but not halocarbon industrial tracers. These air masses were rich in nitrogen relative to sulfur and contained ratios of C 2 H 2 /CO and C 3 H 8 /C 2 H 6 (≈1.5 and 0.1 respectively) indicative of several‐day‐old combustion emissions. It is unclear if these emissions were of Asian origin, or if they were rapidly transported to this region from Europe by the high wind speeds in this tropospheric region (60 – 70 m s −1 ). The significant cyclonic activity over Asia at this time could have transported to the upper troposphere emissions from biomass burning in Southeast Asia or emissions from the extensive use of various biomass materials for cooking and space heating. Apparently, the emissions in the upper troposphere were brought there by wet convective systems since water‐soluble gases and aerosols were depleted in these air masses. Near 9 km altitude there was a distinct regional outflow that appeared to be heavily influenced by biogenic processes on the Asian continent, especially from the southeastern area. These air masses contained CH 4 in excess of 1800 ppbv, while CO 2 and OCS were significantly depleted (349 – 352 ppmv and 450 – 500 pptv, respectively). This signature seemingly reflected CH 4 emissions from wetlands and rice paddies with coincident biospheric uptake of tropospheric CO 2 and OCS.

The NASA GTE TRACE A mission sampled air over the South Atlantic and western Indian Oceans. Thirteen flight legs were flown within the marine boundary layer (MBL). The MBL was typically the cleanest air sampled (e.g., CH 4 < 1680 ppb, CO < 70 ppb, C 2 H 6 < 400 ppt, C 3 H 8 < 40 ppt, NO x < 15 ppt, and midday NO < 5 ppt) but was overlain by polluted air. The photochemistry of the MBL was influenced by oceanic emissions, surface deposition, and entrainment of pollutants from aloft. Chemical budgets were constructed for several species in the MBL in order to investigate these effects and are presented for ethane, ethylene, propane, propylene, n ‐butane, formic acid (HFo), methylhydroperoxide (CH 3 OOH), oxides of nitrogen (i.e., NO, NO 2 , PAN, HNO 3 ), hydrogen peroxide (H 2 O 2 ), and ozone (O 3 ). A photochemical point model was used to evaluate local chemical production and loss. An entrainment model was used to assess material exchange between the lower free troposphere (FT) and the MBL and a resistance deposition model was used to evaluate material exchange across the air‐sea interface. The results suggested the ocean to be the source of measured alkenes in the MBL and to be the most likely source of the shorter‐lived alkanes: propane and n ‐butane. Ethane was the only hydrocarbon for which input from aloft may have exceeded its photochemical destruction. The estimated hydrocarbon sources from the ocean were in agreement with prior analyses. Transport from the lower FT together with surface loss could not account for measured concentrations of CH 2 O, HFo, and HNO 3 . The transport of peroxyacetylnitrate (PAN) from the FT to the MBL exceeded the rate of HNO 3 production and was more than sufficient to maintain observed NO x levels without having to invoke an oceanic source for NO. The flux of NO x , PAN, and HNO 3 was in balance with the surface deposition flux of HNO 3 . However, the predicted rates of HNO 3 formation from the oxidation of NO 2 and HNO 3 entrainment from aloft were inadequate to maintain observed levels of HNO 3 unless HNO 3 was partitioned between the gas phase and a more slowly depositing aerosol phase. The estimated dry deposition flux of HNO 3 to the South Atlantic during TRACE A, 2–4 × 10 9 molecules cm −2 s −1 , was about 10 times the annual average estimate for this region. The destruction of O 3 within the MBL was found to be exceeded by transport into the MBL from aloft, 6 ± 2 × 10 10 compared to 11 ± 10 × 10 10 molecules cm −2 s −1 . The principal O 3 destruction process was mediated by the formation and surface deposition of H 2 O 2 and CH 3 OOH, 4 ± 4 × 10 10 and 1.1 ± 0.5 × 10 10 molecules cm −2 s −1 . The direct loss of O 3 to the sea surface was estimated to be 1.7 ± 0.2 × 10 10 molecules cm −2 s −1 . CH 3 OOH was lost to the sea and transported into the FT from the MBL. Its first‐order loss rate was estimated to be 7 × 10 −6 s −1 for a mean MBL height of 700 m. H 2 O 2 and CH 2 O losses from the MBL were estimated at rates of 1.3 × 10 −5 s −1 for both species. The inclusion of surface deposition improved the agreement between predicted and measured concentrations of HNO 3 , CH 3 OOH, H 2 O 2 , and CH 2 O. However, model CH 2 O remained significantly greater than that measured in the MBL.

Abstract. Volatile organic compounds (VOCs) and carbonaceous aerosol were measured at a sub-urban site near Mexico City in March of 2006 during the MILAGRO study (Megacity Initiative: Local and Global Research Objectives). Diurnal variations of hydrocarbons, elemental carbon (EC) and hydrocarbon-like organic aerosol (HOA) were dominated by a high peak in the early morning when local emissions accumulated in a shallow boundary layer, and a minimum in the afternoon when the emissions were diluted in a significantly expanded boundary layer and, in case of the reactive gases, removed by OH. In comparison, diurnal variations of species with secondary sources such as the aldehydes, ketones, oxygenated organic aerosol (OOA) and water-soluble organic carbon (WSOC) stayed relatively high in the afternoon indicating strong photochemical formation. Emission ratios of many hydrocarbon species relative to CO were higher in Mexico City than in the U.S., but we found similar emission ratios for most oxygenated VOCs and organic aerosol. Secondary formation of acetone may be more efficient in Mexico City than in the U.S., due to higher emissions of alkane precursors from the use of liquefied petroleum gas. Secondary formation of organic aerosol was similar between Mexico City and the U.S. Combining the data for all measured gas and aerosol species, we describe the budget of total observed organic carbon (TOOC), and find that the enhancement ratio of TOOC relative to CO is conserved between the early morning and mid afternoon despite large compositional changes. Finally, the influence of biomass burning is investigated using the measurements of acetonitrile, which was found to correlate with levoglucosan in the particle phase. Diurnal variations of acetonitrile indicate a contribution from local burning sources. Scatter plots of acetonitrile versus CO suggest that the contribution of biomass burning to the enhancement of most gas and aerosol species was not dominant and perhaps not dissimilar from observations in the U.S.

Abstract. Radiocarbon samples taken over Mexico City and the surrounding region during the MILAGRO field campaign in March 2006 exhibited an unexpected distribution: (1) relatively few samples (23%) were below the North American free tropospheric background value (57±2‰) despite the fossil fuel emissions from one of the world's most highly polluted environments; and (2) frequent enrichment well above the background value was observed. Correlate source tracer species and air transport characteristics were examined to elucidate influences on the radiocarbon distribution. Our analysis suggests that a combination of radiocarbon sources biased the "regional radiocarbon background" above the North American value thereby decreasing the apparent fossil fuel signature. Likely sources include the release of 14C-enhanced carbon from bomb 14C sequestered in plant carbon pools via the ubiquitous biomass burning in the region as well as the direct release of radiocarbon as CO2 from other "hot" sources. Plausible perturbations from local point "hot" sources include the burning of hazardous waste in cement kilns; medical waste incineration; and emissions from the Laguna Verde Nuclear Power Plant. These observations provide insight into the use of Δ14CO2 to constrain fossil fuel emissions in the megacity environment, indicating that underestimation of the fossil fuel contribution to the CO2 flux is likely wherever biomass burning coexists with urban emissions and is unaccounted for as a source of the elevated CO2 observed above local background. Our findings increase the complexity required to quantify fossil fuel-derived CO2 in source-rich environments characteristic of megacities, and have implications for the use of Δ14CO2 observations in evaluating bottom-up emission inventories and their reliability as a tool for validating national emission claims of CO2 within the framework of the Kyoto Protocol.