Publications

Abstract Halogenated very short lived substances (VSLS) affect the ozone budget in the atmosphere. Brominated VSLS are naturally emitted from the ocean, and current oceanic emission inventories vary dramatically. We present a new global oceanic emission inventory of Br‐VSLS (bromoform and dibromomethane), considering the physical forcing in the ocean and the atmosphere, as well as the ocean biogeochemistry control. A data‐oriented machine‐learning emulator was developed to couple the air‐sea exchange with the ocean biogeochemistry. The predicted surface seawater concentrations and the surface atmospheric mixing ratios of Br‐VSLS are evaluated with long‐term, global‐scale observations; and the predicted vertical distributions of Br‐VSLS are compared to the global airborne observations in both boreal summer and winter. The global marine emissions of bromoform and dibromomethane are estimated to be 385 and 54 Gg Br per year, respectively. The new oceanic emission inventory of Br‐VSLS is more skillful than the widely used top‐down approaches for representing the seasonal/spatial variations and the annual means of atmospheric concentrations. The new approach improves the model predictability for the coupled Earth system model and can be used as a basis for investigating the past and future ocean emissions and feedbacks under climate change. This model framework can be used to calculate the bidirectional oceanic fluxes for other compounds of interest.

Abstract. Extensive airborne measurements of non-methane organic gases (NMOGs), methane, nitrogen oxides, reduced nitrogen species, and aerosol emissions from US wild and prescribed fires were conducted during the 2019 NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality campaign (FIREX-AQ). Here, we report the atmospheric enhancement ratios (ERs) and inferred emission factors (EFs) for compounds measured on board the NASA DC-8 research aircraft for nine wildfires and one prescribed fire, which encompass a range of vegetation types. We use photochemical proxies to identify young smoke and reduce the effects of chemical degradation on our emissions calculations. ERs and EFs calculated from FIREX-AQ observations agree within a factor of 2, with values reported from previous laboratory and field studies for more than 80 % of the carbon- and nitrogen-containing species. Wildfire emissions are parameterized based on correlations of the sum of NMOGs with reactive nitrogen oxides (NOy) to modified combustion efficiency (MCE) as well as other chemical signatures indicative of flaming/smoldering combustion, including carbon monoxide (CO), nitrogen dioxide (NO2), and black carbon aerosol. The sum of primary NMOG EFs correlates to MCE with an R2 of 0.68 and a slope of −296 ± 51 g kg−1, consistent with previous studies. The sum of the NMOG mixing ratios correlates well with CO with an R2 of 0.98 and a slope of 137 ± 4 ppbv of NMOGs per parts per million by volume (ppmv) of CO, demonstrating that primary NMOG emissions can be estimated from CO. Individual nitrogen-containing species correlate better with NO2, NOy, and black carbon than with CO. More than half of the NOy in fresh plumes is NO2 with an R2 of 0.95 and a ratio of NO2 to NOy of 0.55 ± 0.05 ppbv ppbv−1, highlighting that fast photochemistry had already occurred in the sampled fire plumes. The ratio of NOy to the sum of NMOGs follows trends observed in laboratory experiments and increases exponentially with MCE, due to increased emission of key nitrogen species and reduced emission of NMOGs at higher MCE during flaming combustion. These parameterizations will provide more accurate boundary conditions for modeling and satellite studies of fire plume chemistry and evolution to predict the downwind formation of secondary pollutants, including ozone and secondary organic aerosol.

Abstract The Community Earth System Model version 2 (CESM2) includes a detailed representation of chemistry throughout the atmosphere in the Community Atmosphere Model with chemistry and Whole Atmosphere Community Climate Model configurations. These model configurations use the Model for Ozone and Related chemical Tracers (MOZART) family of chemical mechanisms, covering the troposphere, stratosphere, mesosphere, and lower thermosphere. The new MOZART tropospheric chemistry scheme (T1) has a number of updates over the previous version (MOZART‐4) in CESM, including improvements to the oxidation of isoprene and terpenes, organic nitrate speciation, and aromatic speciation and oxidation and thus improved representation of ozone and secondary organic aerosol precursors. An evaluation of the present‐day simulations of CESM2 being provided for Climate Model Intercomparison Project round 6 (CMIP6) is presented. These simulations, using the anthropogenic and biomass burning emissions from the inventories specified for CMIP6, as well as online calculation of emissions of biogenic compounds, lightning NO, dust, and sea salt, indicate an underestimate of anthropogenic emissions of a variety of compounds, including carbon monoxide and hydrocarbons. The simulation of surface ozone in the southeast United States is improved over previous model versions, largely due to the improved representation of reactive nitrogen and organic nitrate compounds resulting in a lower ozone production rate than in CESM1 but still overestimates observations in summer. The simulation of tropospheric ozone agrees well with ozonesonde observations in many parts of the globe. The comparison of NO x and PAN to aircraft observations indicates the model simulates the nitrogen budget well.

Extensive observations of tropospheric trace species during the second NASA Global Tropospheric Experiment Western Pacific Exploratory Mission (PEM‐West B) in February‐March 1994 showed significant seasonal variability in comparison with the first mission (PEM‐West A), conducted in September‐October 1991. In this study we adopt a previously established analytical method, i.e., the ratio C 2 H 2 /CO as a measure of the relative degree of atmospheric processing, to elucidate the key similarities and variations between the two missions. In addition, the C 2 H 2 /CO ratio scheme is combined with the back‐trajectory‐based and the LIDAR‐based air mass classification schemes, respectively, to make in‐depth analysis of the seasonal variation between PEM‐West A and PEM‐West B (hereinafter referred to as PEM‐WA and PEM‐WB). A large number of compounds, including long‐lived NMHCs, CH 4 , and CO 2 , are, as expected, well correlated with the ratio C 2 H 2 /CO. In comparison with PEM‐WA, a significantly larger range of observed C 2 H 2 /CO values at the high end for the PEM‐WB period indicates that the western Pacific was more impacted by “fresher” source emissions, i.e., faster or more efficient continental outflow. As in the case of PEM‐WA, the C 2 H 2 /CO scheme complements the back‐trajectory air mass classification scheme very well. By combining the two schemes, we found that the atmospheric processing in the region is dominated by atmospheric mixing for the trace species analyzed. This PEM‐WB wintertime result is similar to that found in PEM‐WA for the autumn. In both cases, photochemical reactions are found to play a significant role in determining the background mixing ratios of trace gases, and in this way the two processes are directly related and dependent upon each other. This analysis also indicates that many of the upper tropospheric air masses encountered over the western Pacific during PEM‐WB may have had little impact from eastern Asia's continental surface sources. NO x mixing ratios were significantly enhanced during PEM‐WB when compared with PEM‐WA, in the upper troposphere's more atmospherically processed air masses. These high levels of NO x resulted in a substantial amount of photochemical production of O 3 . A lack of corresponding enhancements in surface emission tracers strongly implies that in situ atmospheric sources such as lightning are responsible for the enhanced upper tropospheric NO x . The similarity in NO x values between the northern (higher air traffic) and southern continental air masses together with the indications of a large seasonal shift suggests that aircraft emissions are not the dominant source. However, photochemical recycling cannot be ruled out as this in situ source of NO x .

Hydrogen peroxide and methylhydroperoxide were measured in the troposphere over the western North Pacific as part of the airborne portion of NASA's Global Tropospheric Experiment/Pacific Exploratory Mission‐West A field mission. The flights circled the North Pacific, focusing on the western Pacific, and extended from 300 to 13,000 m altitude. The hydroperoxides were uniquely separated and quantified using a high‐pressure liquid chromatography system in conjunction with a continuous enzyme fluorometric instrument. Results show a latitudinal gradient in both peroxides at all altitudes; for example, between 3 and 5 km, H 2 O 2 median values decrease from 1700 to 500 parts per trillion by volume (pptv) in going from 0°–15°N to 45°–60°N, and the corresponding decrease in CH 3 OOH was 1100 to 200 pptv. Concentration maxima are observed in both species at altitudes of 2 to 3 km with H 2 O 2 concentrations below 1 km lower by 30%, 10% for CH 3 OOH, and even lower, by a factor of 10, for both above 9 km. The H 2 O 2 to CH 3 OOH ratio increased with altitude and latitude with ratios <1 in the tropical surface layer and >2 at midlatitude high altitude. Highest peroxide concentrations were encountered over the Celebes Sea in air which was impacted by aged biomass fire and urban pollutants. CH 3 OOH was below the level of detection in stratospheric air. H 2 O 2 exceeded SO 2 95% of the time, with the exceptions generally above 9 km. Above 3 km, O 3 increases with decreasing H 2 O 2 and CH 3 OOH. Below 3 km the O 3 ‐CH 3 OOH trend is the same but O 3 increases with increasing H 2 O 2 . The measurements are compared with predictions based upon a photochemical steady state zero‐dimensional model and a three‐dimensional mesoscale time‐dependent model. These models capture observed trends in H 2 O 2 and CH 3 OOH, with the possible exception of H 2 O 2 below 2 km where surface removal is important. A surface removal lifetime of 3.5 days brings the observed and zero‐dimensional model‐estimated H 2 O 2 into agreement. The steady state model suggests a strong correlation between the ratios of NO/CO or HO 2 /HO and the ratio of H 2 O 2 /CH 3 OOH. The observed hydroperoxide ratios bracket the modeled relationship with occasionally much lower H 2 O 2 than expected.

Airborne measurements of CH 2 O were acquired employing tunable diode laser absorption spectroscopy during the 2001 Transport and Chemical Evolution Over the Pacific (TRACE‐P) study onboard NASA's DC‐8 aircraft. Above ∼2.5 km, away from the most extreme pollution influences and heavy aerosol loadings, comprehensive comparisons with a steady state box model revealed agreement to within ±37 pptv in the measurement and model medians binned according to altitude and longitude. Likewise, a near unity slope (0.98 ± 0.03) was obtained from a bivariate fit of the measurements, averaged into 25 pptv model bins, versus the modeled concentrations for values up to ∼450 pptv. Both observations suggest that there are no systematic biases on average between CH 2 O measurements and box model results out to model values ∼450 pptv. However, the model results progressively underpredict the observations at higher concentrations, possibly due to transport effects unaccounted for in the steady state model approach. The assumption of steady state also appears to contribute to the scatter observed in the point‐by‐point comparisons. The measurement‐model variance was further studied employing horizontal flight legs. For background legs screened using a variety of nonmethane hydrocarbon (NMHC) tracers, measurement and model variance agreed to within 15%. By contrast, measurement variance was ∼60% to 80% higher than the model variance, even with small to modest elevations in the NMHC tracers. Measurement‐model comparisons of CH 2 O in clouds and in the lower marine troposphere in the presence of marine aerosols suggest rather significant CH 2 O uptake by as much as 85% in one extreme case compared to expectations based on modeled gas phase processes.

Abstract One of the objectives of the Deep Convective Clouds and Chemistry (DC3) field experiment was to determine the scavenging of soluble trace gases by thunderstorms. We present an analysis of scavenging of hydrogen peroxide (H 2 O 2 ) and methyl hydrogen peroxide (CH 3 OOH) from six DC3 cases that occurred in Oklahoma and northeast Colorado. Estimates of H 2 O 2 scavenging efficiencies are comparable to previous studies ranging from 79 to 97% with relative uncertainties of 5–25%. CH 3 OOH scavenging efficiencies ranged from 12 to 84% with relative uncertainties of 18–558%. The wide range of CH 3 OOH scavenging efficiencies is surprising, as previous studies suggested that CH 3 OOH scavenging efficiencies would be <10%. Cloud chemistry model simulations of one DC3 storm produced CH 3 OOH scavenging efficiencies of 26–61% depending on the ice retention factor of CH 3 OOH during cloud drop freezing, suggesting ice physics impacts CH 3 OOH scavenging. The highest CH 3 OOH scavenging efficiencies occurred in two severe thunderstorms, but there is no obvious correlation between the CH 3 OOH scavenging efficiency and the storm thermodynamic environment. We found a moderate correlation between the estimated entrainment rates and CH 3 OOH scavenging efficiencies. Changes in gas‐phase chemistry due to lightning production of nitric oxide and aqueous‐phase chemistry have little effect on CH 3 OOH scavenging efficiencies. To determine why CH 3 OOH can be substantially removed from storms, future studies should examine effects of entrainment rate, retention of CH 3 OOH in frozen cloud particles during drop freezing, and lightning‐NO x production.

Abstract. In this study, the WRF-Chem v4.4 model was utilized to evaluate three bottom-up emission inventories (EDGAR-HTAP v2, v3, and KORUS v5) using surface and aircraft data in East Asia during the Korea-United States Air Quality (KORUS-AQ) campaign period in 2016. All emission inventories were found to reproduce the diurnal variations of O3 and NO2 as compared to the surface monitor data. However, the spatial distributions of the daily maximum 8-hour average (MDA8) O3 in the model do not completely align with the observations. The model MDA8 O3 had a negative (positive) bias north (south) of 30° N over China. All simulations underestimated the observed CO by 50–60 % over China and South Korea. In the Seoul Metropolitan Area (SMA), EDGAR-HTAP v2, v3, and KORUS v5 simulated the vertical shapes and diurnal patterns of O3 and other precursors effectively, but the model underestimated the observed O3, CO and HCHO concentrations. Notably, the model aromatic VOCs were significantly underestimated with the three bottom-up emission inventories, although the KORUS v5 shows improvements. The model isoprene estimations had a positive bias relative to the observations, suggesting that the Model of Emissions of Gases and Aerosols from Nature (MEGAN) version 2.04 overestimated isoprene emissions. Additional model simulations were conducted by doubling CO and VOC emissions over China and South Korea to investigate the causes of the model O3 biases and the effects of the long-range transport on the O3 over South Korea. The doubled CO and VOC emission simulations improved the model O3 simulations for the local emission dominant case, but led to the model O3 overestimations for the transport dominant case, which emphasizes the need for accurate representations of the local VOC emissions over South Korea.

Since 2012, studies in mice, rats, and humans have suggested that abnormalities in purinergic signaling may be a final common pathway for many genetic and environmental causes of autism spectrum disorder (ASD). The current study in mice was conducted to characterize the bioenergetic, metabolomic, breathomic, and behavioral features of acute hyperpurinergia triggered by systemic injection of the purinergic agonist and danger signal, extracellular ATP (eATP). Responses were studied in C57BL/6J mice in the maternal immune activation (MIA) model and controls. Basal metabolic rates and locomotor activity were measured in CLAMS cages. Plasma metabolomics measured 401 metabolites. Breathomics measured 98 volatile organic compounds. Intraperitoneal eATP dropped basal metabolic rate measured by whole body oxygen consumption by 74% ± 6% (mean ± SEM) and rectal temperature by 6.2˚ ± 0.3˚C in 30 minutes. Over 200 metabolites from 37 different biochemical pathways where changed. Breathomics showed an increase in exhaled carbon monoxide, dimethylsulfide, and isoprene. Metabolomics revealed an acute increase in lactate, citrate, purines, urea, dopamine, eicosanoids, microbiome metabolites, oxidized glutathione, thiamine, niacinamide, and pyridoxic acid, and decreased folate-methylation-1-carbon intermediates, amino acids, short and medium chain acyl-carnitines, phospholipids, ceramides, sphingomyelins, cholesterol, bile acids, and vitamin D similar to some children with ASD. MIA animals were hypersensitive to postnatal exposure to eATP or poly(IC), which produced a rebound increase in body temperature that lasted several weeks before returning to baseline. Acute hyperpurinergia produced metabolic and behavioral changes in mice. The behaviors and metabolic changes produced by ATP injection were associated with mitochondrial functional changes that were profound but reversible.

NASA's Atmospheric Boundary Layer Experiment conducted during the summer of 1990 focused on the distribution of trace species in central and northeastern Canada (altitudes <6 km) and the importance of surface sources/sinks, local emissions, distant transport, tropospheric/stratospheric exchange. Aircraft flights were based from North Bay, Ontario, and Goose Bay, Labrador, Canada. As part of the aircraft measurements, aerosol number density (0.2‐ to 3‐μ diameter) was measured using an optical laser technique. Results show that summertime aerosol budgets of central and northeastern Canada can be significantly impacted by the transport of pollutants from distant source regions. Biomass burning in Alaska and western and central Canada exerts major influences on regional aerosol budgets. Urban emissions transported from the U.S./Canadian border regions are also important. Aerosol enhancements (mixed layer and free troposphere) were most prevalent in air with carbon monoxide mixing ratios >110 parts per billion by volume (ppbv). When data were grouped as to the source of the air (5‐day back trajectories) either north or south of the polar jet, aerosol number density in the mixed layer showed a tendency to be enhanced for air south of the jet relative to north of the jet. However, this difference was not observed for measurements at the higher altitudes (4 to 6 km). For some flights, mixed layer aerosol number densities were >100 higher than free‐tropospheric values (3‐ to 6‐km altitude). The majority of the observed mixed layer enhancement was associated with transport of effluent‐rich air into the Canadian regions. Aerosol emissions from natural Canadian ecosystems were relatively small when compared to transport.

Abstract. Glyoxal (CHOCHO), the simplest dicarbonyl in the troposphere, is an important precursor for secondary organic aerosol (SOA) and brown carbon (BrC) affecting air-quality and climate. The airborne measurement of CHOCHO concentrations during the KORUS-AQ (KORea-US Air Quality study) campaign in 2016 enables detailed quantification of loss mechanisms, pertaining to SOA formation in the real atmosphere. The production of this molecule was mainly from oxidation of aromatics (59 %) initiated by hydroxyl radical (OH), of which glyoxal forming mechanisms are relatively well constrained. CHOCHO loss to aerosol was found to be the most important removal path (69 %) and contributed to roughly ~20 % (3.7 μg sm−3 ppmv−1 hr−1, normalized with excess CO) of SOA growth in the first 6 hours in Seoul Metropolitan Area. To our knowledge, we show the first field observation of aerosol surface-area (Asurf)-dependent CHOCHO uptake, which diverges from the simple surface uptake assumption as Asurf increases in ambient condition. Specifically, under the low (high) aerosol loading, the CHOCHO effective uptake rate coefficient, keff,uptake, linearly increases (levels off) with Asurf, thus, the irreversible surface uptake is a reasonable (unreasonable) approximation for simulating CHOCHO loss to aerosol. Dependency of photochemical impact, as well as aerosol viscosity, are discussed as other possible factors influencing CHOCHO uptake rate. Our inferred Henry's law coefficient of CHOCHO, 7.0 × 108 M atm−1, is ~2 orders of magnitude higher than those estimated from salting-in effects constrained by inorganic salts only, which urges more understanding on CHOCHO solubility under real atmospheric conditions.

Abstract Organic aerosols (OA) represent a significant fraction of total submicron particulate matter (PM 1 ) concentrations globally, including densely populated megacities such as Seoul. However, scientific understanding of the atmospheric formation and removal processes of OA, especially for secondary organic aerosols (SOA), is still highly uncertain. In this study, we examine the characteristics of SOA formation in Seoul during spring‐summer 2016 and fall‐winter 2017/2018, using airborne and ground observations along with a 3‐D global chemical transport model, GEOS‐Chem. We use four different SOA schemes in the model, including simplified and complex volatility‐based frameworks, and evaluate them by comparing the simulations with the observations to examine how our scientific understanding embedded in each SOA scheme affects the observed biases. Our analysis of the model performance of each scheme also provides the most suitable approach in simulating SOA in a typical urban environment. Comparisons of the simulated versus observed OA concentrations show that model biases range from −72% to +118%, with considerable variability among different schemes and seasons. We find that the inclusion of semi/intermediate volatile precursors, in addition to the traditional precursors, and chemical aging (functionalization) are important factors to simulate surface SOA concentrations in Seoul. However, a comparison of observed and simulated SOA/∆CO enhancement ratios suggests that most schemes underpredict SOA aging in upper levels in the boundary layer. We also find that the simplified SOA scheme can reproduce observed OA but often shows overestimation in surface air, indicating that uncertainties exist in bottom‐up emissions and precursor parameterization in Seoul.

Abstract This article explores security cooperation between the Caribbean and Mexico,looking specifically at strategies being pursued to shift the focus in Latin America and the Caribbean from ‘the war on drugs’ to ‘the war on guns’ to address the problem of gun trafficking. This is a shift away from the United States’ priority to that of the region and a move towards a more assertive model of South–South security cooperation. The Caribbean Community and Common Market’s (CARICOM’s) strategy to support Mexico’s tortious and historic lawsuit against American gun manufacturers and to declare a ‘war on guns’ reflects its inability to independently influence the United States’ priorities within the region. Mexico, a Southern country, makes a difference because of its geopolitical relevance to the US, their shared border, and Washington’s attempt to stop the flow of Mexican immigration. We read the Mexico–Caribbean coalition as a significant development in South–South security cooperation (SSSC). Our analysis contributes to an understanding of the nuances and complexities of security cooperation, capacities for scaling up action through SSSC, and the political and legal manoeuvrings involved in challenging hierarchies of power between the so-called global North and South.