Publications

Abstract. We determine enhancement ratios for NOx, PAN, and other NOy species from boreal biomass burning using aircraft data obtained during the ARCTAS-B campaign and examine the impact of these emissions on tropospheric ozone in the Arctic. We find an initial emission factor for NOx of 1.06 g NO per kg dry matter (DM) burned, much lower than previous observations of boreal plumes, and also one third the value recommended for extratropical fires. Our analysis provides the first observational confirmation of rapid PAN formation in a boreal smoke plume, with 40% of the initial NOx emissions being converted to PAN in the first few hours after emission. We find little clear evidence for ozone formation in the boreal smoke plumes during ARCTAS-B in either aircraft or satellite observations, or in model simulations. Only a third of the smoke plumes observed by the NASA DC8 showed a correlation between ozone and CO, and ozone was depleted in the plumes as often as it was enhanced. Special observations from the Tropospheric Emission Spectrometer (TES) also show little evidence for enhanced ozone in boreal smoke plumes between 15 June and 15 July 2008. Of the 22 plumes observed by TES, only 4 showed ozone increasing within the smoke plumes, and even in those cases it was unclear that the increase was caused by fire emissions. Using the GEOS-Chem atmospheric chemistry model, we show that boreal fires during ARCTAS-B had little impact on the median ozone profile measured over Canada, and had little impact on ozone within the smoke plumes observed by TES.

Abstract. Observations of a comprehensive suite of inorganic and organic trace gases, including non-methane hydrocarbons (NMHCs), halogenated organics and oxygenated volatile organic compounds (OVOCs), obtained from the NASA DC-8 over Canada during the ARCTAS aircraft campaign in July 2008 illustrate that convection is important for redistributing both long- and short-lived species throughout the troposphere. Convective outflow events were identified by the elevated mixing ratios of organic species in the upper troposphere relative to background conditions. Several dramatic events were observed in which isoprene and its oxidation products were detected at hundreds of pptv at altitudes higher than 8 km. Two events are studied in detail using detailed experimental data and the NASA Langley Research Center (LaRC) box model. One event had no lightning NOx (NO + NO2) associated with it and the other had substantial lightning NOx (LNOx > 1 ppbv). When convective storms transport isoprene from the boundary layer to the upper troposphere and no LNOx is present, OH is reduced due to scavenging by isoprene, which serves to slow the chemistry, resulting in longer lifetimes for species that react with OH. Ozone and PAN production is minimal in this case. In the case where isoprene is convected and LNOx is present, there is a large effect on the expected ensuing chemistry: isoprene exerts a dominant impact on HOx and nitrogen-containing species; the relative contribution from other species to HOx, such as peroxides, is insignificant. The isoprene reacts quickly, resulting in primary and secondary products, including formaldehyde and methyl glyoxal. The model predicts enhanced production of alkyl nitrates (ANs) and peroxyacyl nitrate compounds (PANs). PANs persist because of the cold temperatures of the upper troposphere resulting in a large change in the NOx mixing ratios which, in turn, has a large impact on the HOx chemistry. Ozone production is substantial during the first few hours following the convection to the UT, resulting in a net gain of approximately 10 ppbv compared to the modeled scenario in which LNOx is present but no isoprene is present aloft.

Abstract Recent measurements over the Northern Hemisphere indicate that the long‐term decline in the atmospheric burden of ethane (C 2 H 6 ) has ended and the abundance increased dramatically between 2010 and 2014. The rise in C 2 H 6 atmospheric abundances has been attributed to oil and natural gas extraction in North America. Existing global C 2 H 6 emission inventories are based on outdated activity maps that do not account for current oil and natural gas exploitation regions. We present an updated global C 2 H 6 emission inventory based on 2010 satellite‐derived CH 4 fluxes with adjusted C 2 H 6 emissions over the U.S. from the National Emission Inventory (NEI 2011). We contrast our global 2010 C 2 H 6 emission inventory with one developed for 2001. The C 2 H 6 difference between global anthropogenic emissions is subtle (7.9 versus 7.2 Tg yr −1 ), but the spatial distribution of the emissions is distinct. In the 2010 C 2 H 6 inventory, fossil fuel sources in the Northern Hemisphere represent half of global C 2 H 6 emissions and 95% of global fossil fuel emissions. Over the U.S., unadjusted NEI 2011 C 2 H 6 emissions produce mixing ratios that are 14–50% of those observed by aircraft observations (2008–2014). When the NEI 2011 C 2 H 6 emission totals are scaled by a factor of 1.4, the Goddard Earth Observing System Chem model largely reproduces a regional suite of observations, with the exception of the central U.S., where it continues to underpredict observed mixing ratios in the lower troposphere. We estimate monthly mean contributions of fossil fuel C 2 H 6 emissions to ozone and peroxyacetyl nitrate surface mixing ratios over North America of ~1% and ~8%, respectively.

Abstract. The Sulfur Transport and dEposition Model (STEM) developed at the University of Iowa is applied to the analysis of observations obtained during the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B), conducted over the Pacific Ocean during the 2006 North American spring season. This paper reports on the model performance of meteorological parameters, trace gases, aerosols and photolysis rate (J-values) predictions with the NASA DC-8 and NSF/NCAR C-130 airborne measurements along with observations from three surface sites Mt. Bachelor, Trinidad Head and Kathmandu, Nepal. In general the model shows appreciable skill in predicting many of the important aspects of the observed distributions. The major meteorological parameters driving long range transport are accurately predicted by the WRF simulations used in this study. Furthermore, the STEM model predicts aerosols and trace gases concentrations within a standard deviation of most of the observed mean values. The results also point towards areas where model improvements are needed; e.g., the STEM model underestimates CO (15% for the DC8 and 6% for the C-130), whereas it overpredicts PAN (by a factor of two for both aircraft). The errors in the model calculations are attributed to uncertainty in emissions estimates and uncertainty in the top and lateral boundary conditions. Results from a series of sensitivity simulations examining the impact of the growth of emissions in Asia from 2000 to 2006, the importance of biomass burning, the effect of using boundary conditions from different global models, and the role of heterogeneous chemistry on the predictions are also presented. The impacts of heterogeneous reactions at specific times during dust transport episodes can be significant, and in the presence of dust both sulfate and nitrate aerosol production is increased and gas phase nitric acid levels are reduced appreciably (~50%). The aging of the air masses during the long range transport over the Pacific and the impact of various sources (source regions as well as energy and biomass burning) on targeted observations are analyzed using back-trajectories and tagged CO-tracer analysis.

<strong class="journal-contentHeaderColor">Abstract.</strong> Bromine released from the decomposition of short-lived brominated source gases contributes as a sink of ozone in the lower stratosphere. The two major contributors are <span class="inline-formula">CH₂Br₂</span> and <span class="inline-formula">CHBr₃</span>. In this study, we investigate the global seasonal distribution of these two substances, based on four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission. Observations of <span class="inline-formula">CH₂Br₂</span> in the free and upper troposphere indicate a pronounced seasonality in both hemispheres, with slightly larger mixing ratios in the Northern Hemisphere (NH). Compared to <span class="inline-formula">CH₂Br₂</span>, <span class="inline-formula">CHBr₃</span> in these regions shows larger variability and less clear seasonality, presenting larger mixing ratios in winter and autumn in NH midlatitudes to high latitudes. The lowermost stratosphere of SH and NH shows a very similar distribution of <span class="inline-formula">CH₂Br₂</span> in hemispheric spring with differences well below 0.1 ppt, while the differences in hemispheric autumn are much larger with substantially smaller values in the SH than in the NH. This suggests that transport processes may be different in both hemispheric autumn seasons, which implies that the influx of tropospheric air ("flushing") into the NH lowermost stratosphere is more efficient than in the SH. The observations of <span class="inline-formula">CHBr₃</span> support the suggestion, with a steeper vertical gradient in the upper troposphere and lower stratosphere in SH autumn than in NH autumn. However, the SH database is insufficient to quantify this difference. We further compare the observations to model estimates of TOMCAT (Toulouse Off-line Model of Chemistry And Transport) and CAM-Chem (Community Atmosphere Model with Chemistry, version 4), both using the same emission inventory of <span class="cit" id="xref_text.1"><a href="#bib1.bibx43">Ordóñez et al.</a> (<a href="#bib1.bibx43">2012</a>)</span>. The pronounced tropospheric seasonality of <span class="inline-formula">CH₂Br₂</span> in the SH is not reproduced by the models, presumably due to erroneous seasonal emissions or atmospheric photochemical decomposition efficiencies. In contrast, model simulations of <span class="inline-formula">CHBr₃</span> show a pronounced seasonality in both hemispheres, which is not confirmed by observations. The distributions of both species in the lowermost stratosphere of the Northern and Southern hemispheres are overall well captured by the models with the exception of southern hemispheric autumn, where both models present a bias that maximizes in the lowest 40 K above the tropopause, with considerably lower mixing ratios in the observations. Thus, both models reproduce equivalent flushing in both hemispheres, which is not confirmed by the limited available observations. Our study emphasizes the need for more extensive observations in the SH to fully understand the impact of <span class="inline-formula">CH₂Br₂</span> and <span class="inline-formula">CHBr₃</span> on lowermost-stratospheric ozone loss and to help constrain emissions.

The Biomass Burning and Lightning Experiment Phase B (BIBLE‐B) aircraft measurement campaign was conducted over the western Pacific and Australia in August and September 1999. In situ aircraft measurements of carbon monoxide (CO), nitric oxide (NO), total reactive nitrogen (NO y ), ozone (O 3 ), nonmethane hydrocarbons (NMHCs), and other species were made during BIBLE‐B. Meteorological analysis shows that the trace gases emitted from biomass burning in northern Australia were mostly confined within the planetary boundary layer (below ∼3 km) by strong subsidence in the free troposphere. Removal processes of NO x (equal to measured NO + calculated NO 2 ) and NO y in biomass burning plumes in the boundary layer are examined on the basis of correlation analysis. The photochemical lifetime of NO x in biomass burning plumes during the daytime is estimated to be 0.1 to 0.3 days using the correlations of NO x with short‐lived NMHCs and hydroxyl radical (OH) concentration calculated from a constrained photochemical model. Correlation of NO y with CO shows that ∼60% of the NO y molecules originating from biomass burning were removed in the boundary layer within 2–3 days. This result is consistent with dry deposition of nitric acid (HNO 3 ) in the plumes. It is likely that only a small fraction of NO y emitted from biomass burning was exported from the boundary layer to the free troposphere during the BIBLE‐B period.

During the Deepwater Horizon (DWH) oil spill, a wide range of gas and aerosol species were measured from an aircraft around, downwind, and away from the DWH site. Additional hydrocarbon measurements were made from ships in the vicinity. Aerosol particles of respirable sizes were on occasions a significant air quality issue for populated areas along the Gulf Coast. Yields of organic aerosol particles and emission factors for other atmospheric pollutants were derived for the sources from the spill, recovery, and cleanup efforts. Evaporation and subsequent secondary chemistry produced organic particulate matter with a mass yield of 8 ± 4% of the oil mixture reaching the water surface. Approximately 4% by mass of oil burned on the surface was emitted as soot particles. These yields can be used to estimate the effects on air quality for similar events as well as for this spill at other times without these data. Whereas emission of soot from burning surface oil was large during the episodic burns, the mass flux of secondary organic aerosol to the atmosphere was substantially larger overall. We use a regional air quality model to show that some observed enhancements in organic aerosol concentration along the Gulf Coast were likely due to the DWH spill. In the presence of evaporating hydrocarbons from the oil, NO(x) emissions from the recovery and cleanup operations produced ozone.

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 onboard 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 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.

Our results demonstrate the feasibility of measuring plasma lipids through breath analysis. Optimization of this technology may ultimately lead to the development of portable breath analyzers for plasma lipids, replacing blood-based bioassays.

We present here results for reactive nitrogen species measured aboard the NASA DC‐8 aircraft during the Transport and Chemical Evolution over the Pacific (TRACE‐P) mission. The large‐scale distributions total reactive nitrogen (NO y,sum = NO + NO 2 + HNO 3 + PAN + C 1 –C 5 alkyl nitrates) and O 3 and CO were better defined in the boundary layer with significant degradation of the relationships as altitude increased. Typically, NO y,sum was enhanced over background levels of ∼260 pptv by 20‐to‐30‐fold. The ratio C 2 H 2 /CO had values of 1–4 at altitudes up to 10 km and as far eastward as 150°E, implying significant vertical mixing of air parcels followed by rapid advection across the Pacific. Analysis air parcels originating from five principal Asian source regions showed that HNO 3 and PAN dominated NO y,sum . Correlations of NO y,sum with C 2 Cl 4 (urban tracer) were not well defined in any of the source regions, and they were only slightly better with CH 3 Cl (biomass tracer). Air parcels over the western Pacific contained a complex mixture of emission sources that are not easily resolvable as shown by analysis of the Shanghai mega‐city plume. It contained an intricate mixture of pollution emissions and exhibited the highest mixing ratios of NO y,sum species observed during TRACE‐P. Comparison of tropospheric chemistry between the earlier PEM‐West B mission and the recent TRACE‐P data showed that in the boundary layer significant increases in the mixing ratios of NO y,sum species have occurred, but the middle and upper troposphere seems to have been affected minimally by increasing emissions on the Asian continent over the last 7 years.