Publications

Comment on acp-2022-631

<strong class="journal-contentHeaderColor">Abstract.</strong> The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze a data set of 10 s (2 km) merged and gap-filled observations of the key reactive species driving the chemical budgets of O<span class="inline-formula">₃</span> and CH<span class="inline-formula">₄</span> (O<span class="inline-formula">₃</span>, CH<span class="inline-formula">₄</span>, CO, H<span class="inline-formula">₂</span>O, HCHO, H<span class="inline-formula">₂</span>O<span class="inline-formula">₂</span>, CH<span class="inline-formula">₃</span>OOH, C<span class="inline-formula">₂</span>H<span class="inline-formula">₆</span>, higher alkanes, alkenes, aromatics, NO<span class="inline-formula">_<i>x</i></span>, HNO<span class="inline-formula">₃</span>, HNO<span class="inline-formula">₄</span>, peroxyacetyl nitrate, and other organic nitrates), consisting of 146 494 distinct air parcels from ATom deployments 1 through 4. Six models calculated the O<span class="inline-formula">₃</span> and CH<span class="inline-formula">₄</span> photochemical tendencies from this modeling data stream for ATom 1. We find that 80 %–90 % of the total reactivity lies in the top 50 % of the parcels and 25 %–35 % in the top 10 %, supporting previous model-only studies that tropospheric chemistry is driven by a fraction of all the air. Surprisingly, the probability densities of species and reactivities averaged on a model scale (100 km) differ only slightly from the 2 km ATom 10 s data, indicating that much of the heterogeneity in tropospheric chemistry can be captured with current global chemistry models. Comparing the ATom reactivities over the tropical oceans with climatological statistics from six global chemistry models, we find generally good agreement with the reactivity rates for O<span class="inline-formula">₃</span> and CH<span class="inline-formula">₄</span>. Models distinctly underestimate O<span class="inline-formula">₃</span> production below 2 km relative to the mid-troposphere, and this can be traced to lower NO<span class="inline-formula">_<i>x</i></span> levels than observed. Attaching photochemical reactivities to measurements of chemical species allows for a richer, yet more constrained-to-what-matters, set of metrics for model evaluation. This paper presents a corrected version of the paper published under the same authors and title (sans “corrected”) as <a href="https://doi.org/10.5194/acp-21-13729-2021">https://doi.org/10.5194/acp-21-13729-2021</a>.

New insights into the column CH₂O/NO₂ ratio as an indicator of near‐surface ozone sensitivity

Abstract Satellite‐based measurements of the column CH 2 O/NO 2 ratio have previously been used to estimate near‐surface ozone (O 3 ) sensitivity (i.e., NO x or VOC limited), and the forthcoming launch of air quality‐focused geostationary satellites provides a catalyst for reevaluating the ability of satellite‐measured CH 2 O/NO 2 to be used in this manner. In this study, we use a 0‐D photochemical box model to evaluate O 3 sensitivity and find that the relative rate of radical termination from radical‐radical interactions to radical‐NO x interactions (referred to as LRO x /LNO x ) provides a good indicator of maximum O 3 production along NO x ridgelines. Using airborne measurements from NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relative to Air Quality (DISCOVER‐AQ) deployments in Colorado, Maryland, and Houston, we show that in situ measurements of CH 2 O/NO 2 can be used to indicate O 3 sensitivity, but there is an important “transition/ambiguous” range whereby CH 2 O/NO 2 fails to categorize O 3 sensitivity, and the range and span of this transition/ambiguous range varies regionally. Then, we apply these findings to aircraft‐derived column density measurements from DISCOVER‐AQ and find that inhomogeneities in vertical mixing in the lower troposphere further degrades the ability of column CH 2 O/NO 2 to indicate near‐surface O 3 sensitivity (i.e., the transition/ambiguous range is much larger than indicated by in situ data alone), and we hypothesize that the global transition/ambiguous range is sufficiently large to make the column CH 2 O/NO 2 ratio unuseful for classifying near‐surface O 3 sensitivity. Lastly, we present a case study from DISCOVER‐AQ‐Houston that suggests that O 3 sensitivity on exceedance days may be substantially different than on nonexceedance days (which may be observable from space) and explore the diurnal evolution of O 3 sensitivity, O 3 production, and the column CH 2 O/NO 2 ratio. The results of these studies suggest that although satellite measurements of CH 2 O/NO 2 alone may not be sufficient for accurately classifying near‐surface O 3 sensitivity, new techniques offered by geostationary platforms may nonetheless provide methods for using space‐based measurements to develop O 3 mitigation strategies.

Processes influencing ozone levels in Alaskan forest fire plumes during long-range transport over the

Aerosol meteorology and Philippine receptor observations of Maritime Continent aerosol emissions for the 2012 7SEAS southwest monsoon intensive study

Abstract. The largest 7 Southeast Asian Studies (7-SEAS) operations period within the Maritime Continent occurred in the 2012 August–September biomass burning season. Included where an enhanced deployment of Aerosol Robotic Network (AERONET) sun photometers, of multiple lidars, and of a Singapore supersite. Simultaneously, a ship was dispatched to the Palawan Archipelago and Sulu Sea of the Philippines for September 2012 to observe transported smoke and pollution as it entered the southwest monsoon monsoonal trough. Here we describe the nature of the overall 2012 southwest monsoon biomass burning season, but focus on the findings of the research cruise and the aerosol meteorology of this convectively active region. This 2012 cruise followed a 2 week cruise in 2011, and was in part consistent with the findings of that cruise for how smoke emission and transport relate to monsoonal flows, the propagation of the Madden Julian Oscillation (MJO), tropical cyclones, and covariance between smoke transport events and the atmosphere’s thermodynamic structure. Aerosol observations in the 2011 cruise also highlighted the importance of squall lines and cold pools as they propagate across the South China Sea, scavenging aerosol particles in their path. For 2012, the cruise experienced differing environments. The monsoonal flow direction was perturbed by easterly waves, leading at times to total flow reversal in the South China Sea. Two category 5 typhoons just east of the Philippines also modulated flow patterns and convection. Whereas in 2011 large synoptic scale aerosol events transported high concentrations of smoke into the Philippines over days, in 2012, measured aerosol events exhibited a much more short term variation, sometimes only over 3–12 hours. Navy Aerosol Analysis and Prediction System (NAAPS) simulations captured longer wavelength aerosol events quite well, but largely failed to capture the timing in high frequency phenomena. Also observed were nucleation events in cleaner and polluted conditions, as well as in urban plumes. Combined, observations indicate pockets of high particle counts are not uncommon in the region. Perhaps most interestingly, several cases of squall lines heralding major aerosol events were observed, as opposed to the previous observations in 2011 of these lines largely scavenging aerosol particles from the marine boundary layer. We hypothesize that these phenomena may originate from weakly forced convection ahead of polluted land breeze fronts caught in strong monsoonal flows. Ultimately, the research findings of the 2012 cruise nicely complement the narrative started by the 2011 research cruise, and point to the importance of small scale phenomena such as sea breezes and squall lines embedded in the large scale monsoonal flow patterns in dominating aerosol lifecycle and potentially effects. “Pure” biomass burning plumes are relatively rare and are usually mixed with significant amounts of anthropogenic pollution.

Comment on egusphere-2024-951

<strong class="journal-contentHeaderColor">Abstract.</strong> The fraction of urban volatile organic compounds (VOC) emissions attributable to fossil fuel combustion has been declining in many parts of the world, resulting in a need to better constrain other anthropogenic sources of these emissions. During the National Institute of Environmental Research (NIER) and National Aeronautics and Space Administration (NASA) Korea-United States Air Quality (KORUS-AQ) field study in Seoul, South Korea during May&ndash;June 2016, air quality models underestimated ozone, formaldehyde, and peroxyacetyl nitrate (PAN) indicating an underestimate of VOCs in the emissions inventory. Here, we use aircraft observations interpreted with the GEOS-Chem chemical transport model to assess the need for increases in VOC emissions. We find that the largest increases are attributable to compounds associated with volatile chemical products, liquefied petroleum gas (LPG) and natural gas emissions, and long-range transport. Revising model chemistry to better match observed VOC speciation together with increasing model emissions of underestimated VOC species increased calculated OH reactivity by +2 s^-1 and ozone production by 2 ppb hr^-1. Ozone increased by 6 ppb below 2 km and 9 ppb at the surface, and formaldehyde and acetaldehyde increased by 30 % and 120 % aloft, respectively, all in better agreement with observations. The larger increase in acetaldehyde was attributed to ethanol emissions which we found to be as important for ozone production as isoprene or alkenes. The increased acetaldehyde largely resolved the model PAN bias. The need for additional unmeasured VOCs however was indicated by a remaining model bias of -1 ppb in formaldehyde and 57 % and 52 % underestimate in higher peroxynitrates (PNs) and alkyl nitrates (ANs), respectively. We added additional chemistry to the model to represent an additional six PNs from observed VOCs but were unable to account for the majority of missing PNs. However, four of these PNs were modeled at concentrations similar to other commonly measured PNs (&gt;2 % of PAN) indicating that these should be measured in future campaigns. We hypothesize that emissions of oxygenated VOCs (OVOCs) such as &gt;C5 aldehydes from cooking and/or alkenes associated with volatile chemical products could produce both PNs and ANs and improve remaining model biases. Emerging research on the emissions and chemistry of these species will soon allow for modeling of their impact on local and regional photochemistry.

Seasonal and spatial variation in atmospheric hydroxyl and hydroperoxyl: comparison to a photochemical box model.

Atmospheric measurements of peroxyacetyl nitrate and other organic nitrates at high latitudes: Possible sources and sinks

Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO 2 , HNO 3 , peroxypropionyl nitrate (PPN), CH 3 ONO 2 , NO y ) were performed at high latitudes over North America and Greenland during July–August 1988, at all altitudes between 0 and 6 km as part of an Arctic Boundary Layer Expedition (ABLE 3A). Complementing these were measurements of C 1 to C 5 hydrocarbons, O 3 , chemical tracers (C 2 Cl 4 , CO), and important meteorological parameters. PAN was found to be an important reactive nitrogen species in the free troposphere, with 95% of the mixing ratios falling in the range of 5 to 450 ppt. PAN increased systematically with height with mixing ratios of 100–700 ppt at 6 km and 0–50 ppt in the boundary layer. The free tropospheric PAN reservoir was present over the entire high‐latitude region sampled (50° to 82°N latitude and 60° to 160°W longitude). In the boundary layer, PAN mixing ratios were higher over land than over the North Pacific Ocean. Significant levels of PAN were measured within stratospheric intrusions, forest fire plumes, and episodes of remote pollution. Other organic nitrates such as PPN and CH 3 ONO 2 were found to be a small fraction of PAN (0–10%). PAN and O 3 were strongly correlated both in their fine and gross structures, and the latitudinal distribution of PAN in the free troposphere followed that of O 3 . A two dimensional global photochemical model is used to compare measurements and model results. Model simulations, correlations between reactive nitrogen species (e.g. PAN and NO y ) and anthropogenic tracers (C 2 H 2 , CO, C 2 Cl 4 ), and the composition of NO y itself support the view that the reactive nitrogen measured during ABLE 3 A is predominantly of anthropogenic origin with a minor stratospheric component. Transported industrial pollution, biomass burning, and the unique seasonal dynamics of the Arctic/sub‐Arctic region play a dominant role in defining this reactive nitrogen abundance. This PAN (and NO y ) reservoir may contribute to the summertime maximum in deposited nitrate observed over Greenland.

Nitryl chloride as a 'new' radical source and its role in production of ozone in polluted troposphere: an overview of the results from four field campaigns in China

Clouds and trace gas distributions during TRACE‐P

This paper addresses the question: To what extent do trace gas distributions correspond to cloudiness? Observations taken during NASA's TRACE‐P experiment indicate that there can be statistically significant differences in trace gas concentrations between clear‐sky and cloudy areas. During the TRACE‐P mission, frontal outflow of Asian emissions from the Pacific Rim to the western, North Pacific was sampled by NASA's DC‐8 and P‐3B aircraft. On several occasions, enhanced CO mixing ratios were observed in and around frontal clouds. A more detailed analysis of trace gas distributions revealed CO enhancements of 30% in the lower free troposphere (1–5 km) for cloudy regions as compared to clear areas. These enhancements exist within clouds as well as above and below clouds. In the upper free troposphere (5–11 km), overall enhancement in CO of 15% was observed although enhancements are mainly restricted to observations within clouds. These in‐cloud observations were enhanced by factors of 1.5 to 2 over clear air data. Similar enhancements were seen for many other anthropogenic tracers. By contrast, distributions for O 3 revealed no clear differences between cloudy and clear regions suggesting that other influences (e.g., stratosphere‐troposphere exchange) might complicate any correspondence with local cloudiness. Expected cloud influences on oxidation chemistry were evident in enhanced OH concentrations above clouds and depressed OH below clouds. These findings are particularly relevant to current and future satellite investigations of the troposphere. Understanding the potential biases created by the inability to probe cloudy regions will improve the interpretation of regional and globally averaged satellite observations.

Evidence of secondary organic aerosols formation by non-methane hydrocarbons condensation in cold Pyro-cumulonimbus (pyroCb) outflows

&amp;lt;p&amp;gt;Particle and trace gas emissions can undergo rapid changes in the atmosphere as a result of evaporation, condensation, and coagulation processes that are driven by dynamics and photochemistry.&amp;amp;#160; Here we analyze the fate of non-methane hydrocarbons (NMHCs) gases emitted by intense fires associated with pyroCbs towers that rise and cool rapidly and undergo relatively little dilution as they loft smoke into the upper troposphere and lower stratosphere.&amp;amp;#160; We use airborne observations of plumes from the Williams Flats Fire over the continental United States taken during 2019 FIREX-AQ campaign.&amp;amp;#160; Trace gas data from both fresh boundary smoke and PyroCb-lofted smoke from this fire are compared to that from smoke plumes that stayed at lower altitudes to constrain the roles of condensation, cloud processing and photochemistry in the outflow of pyroCbs.&amp;amp;#160; In the pyroCb outflows we observe lower CO normalized NMHCs mixing ratios with low vapor pressure compared to the boundary layer samples while for high vapor pressure compounds there is little difference between the CO normalized NMHC mixing ratios observed in the different fresh smoke plumes.&amp;amp;#160; Associated with this decrease in condensable NMHCs we find an increase in particle concentrations, specifically at large sizes (~350nm). These multiple observational facts are used to estimate the secondary organic aerosol production by NMHC condensation in pyroCb.&amp;amp;#160; Further analysis of FIREX-AQ data will be used to elucidate the roles of solubility and photochemistry on SOA formation in pyroCbs. These FIREX-AQ results will be used to inform cloud resolving large eddy simulation (LES, HIGRAD) to examine deep convective fire impacts on long range smoke impacts on climate and air quality.&amp;lt;/p&amp;gt;

Measurements of volatile organic compounds at a suburban ground site (T1) in Mexico City during the MILAGRO 2006 campaign: measurement comparison, emission ratios, and source attribution

Abstract. Volatile organic compound (VOC) mixing ratios were measured with two different instruments at the T1 ground site in Mexico City during the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign in March of 2006. A gas chromatograph with flame ionization detector (GC-FID) quantified 18 light alkanes, alkenes and acetylene while a proton-transfer-reaction ion-trap mass spectrometer (PIT-MS) quantified 12 VOC species including oxygenated VOCs (OVOCs) and aromatics. A GC separation system was used in conjunction with the PIT-MS (GC-PIT-MS) to evaluate PIT-MS measurements and to aid in the identification of unknown VOCs. The VOC measurements are also compared to simultaneous canister samples and to two independent proton-transfer-reaction mass spectrometers (PTR-MS) deployed on a mobile and an airborne platform during MILAGRO. VOC diurnal cycles demonstrate the large influence of vehicle traffic and liquid propane gas (LPG) emissions during the night and photochemical processing during the afternoon. Emission ratios for VOCs and OVOCs are determined from early-morning enhancement ratios and compared to emission ratios calculated from the PMF results. Average emission ratios for non-oxygenated species relative to CO are on average a factor of 2 higher than measured for US cities. Emission ratios for OVOCs are estimated and compared to literature values the northeastern US and to tunnel studies in California. Positive matrix factorization analysis (PMF) is used to provide insight into VOC sources and processing and to estimate OVOC emission ratios. Three PMF factors were distinguished by the analysis including the emissions from vehicles, the use of liquid propane gas and the production of secondary VOCs + long-lived species. The total PIT-MS signal was summed to estimate the fraction of identified vs. unidentified VOC species.

Formaldehyde column density measurements as a suitable pathway to estimate near‐surface ozone tendencies from space

In support of future satellite missions that aim to address the current shortcomings in measuring air quality from space, NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign was designed to enable exploration of relationships between column measurements of trace species relevant to air quality at high spatial and temporal resolution. In the DISCOVER-AQ data set, a modest correlation (<i>r</i> ² = 0.45) between ozone (O₃) and formaldehyde (CH₂O) column densities was observed. Further analysis revealed regional variability in the O₃-CH₂O relationship, with Maryland having a strong relationship when data were viewed temporally and Houston having a strong relationship when data were viewed spatially. These differences in regional behavior are attributed to differences in volatile organic compound (VOC) emissions. In Maryland, biogenic VOCs were responsible for ~28% of CH₂O formation within the boundary layer column, causing CH₂O to, in general, increase monotonically throughout the day. In Houston, persistent anthropogenic emissions dominated the local hydrocarbon environment, and no discernable diurnal trend in CH₂O was observed. Box model simulations suggested that ambient CH₂O mixing ratios have a weak diurnal trend (±20% throughout the day) due to photochemical effects, and that larger diurnal trends are associated with changes in hydrocarbon precursors. Finally, mathematical relationships were developed from first principles and were able to replicate the different behaviors seen in Maryland and Houston. While studies would be necessary to validate these results and determine the regional applicability of the O₃-CH₂O relationship, the results presented here provide compelling insight into the ability of future satellite missions to aid in monitoring near-surface air quality.

Analysis of Coal-Mine-Fire Gas

晩春のPEACE-B航空機調査で観測した,太平洋へのアジアからの化学物質の流出

Issues with Understanding Atmospheric Oxidation and Ozone Production during KORUS-AQ

Towards an Understanding of Atmospheric Methanol

Summertime tropospheric observations related to N_<i>x</i> O_<i>y</i> distributions and partitioning over Alaska: Arctic Boundary Layer Expedition 3A

Measurements of the reactive odd nitrogen compounds NO, NO 2 , peroxyacetyl nitrate (PAN), and NO y are presented for the summertime middle/lower troposphere (6.1–0.15 km) over northern high latitudes. In addition, the chemical signatures revealed from concurrent measurements of O 3 , CO, C 2 H 2 , C 2 H 6 , C 3 H 8 , C 2 Cl 4 , and H 2 O are used to further characterize factors affecting the budget and distribution of N x O y , in the Arctic and sub‐Arctic tropospheric air masses sampled over Alaska during the NASA Arctic Boundary Layer Expedition (ABLE 3A) field campaign. Many of the compounds listed above exhibited a general trend of median mixing ratios increasing in proportion with altitude within the lower 6‐km column. However, median mixing ratios of NO and NO x (NO + NO 2 ) were nearly independent of altitude, having values of about 8.5 and 25 pptv, respectively. Median mixing ratios of NO y varied from about 350 pptv within the lowest altitudes to about 600 pptv within the highest altitudes sampled. PAN constituted the largest fraction of NO y (∼50%) at the highest altitudes. In addition, PAN mixing ratios accounted for all of the approximate 60 pptv/km altitudinal dependency in NO y . The analyses presented implicate biomass burning in Siberia as the probable source of about one‐third of the NO y abundance within the middle/lower troposphere over Alaska. These analyses also implicate the downward transport of air from altitudes in the vicinity of the tropopause as a major contributor to the abundance of NO y , (∼30–50%) within the lower 6‐km column over Alaska. However, the exact origin of this high‐altitude NO y remains uncertain. The impact of lower latitude industrial/urban pollution also remains largely uncertain, although various chemical signatures imply inputs from these regions would have been relatively well aged (15–30 days).

Investigations of ROx Radical Photochemistry During the MCMA-2006 Field Campaign

Whole Air Sampling During NASA's March-April 1999 Pacific Exploratory Expedition (PEM-Tropics B)

University of California, Irvine (UCI) collected more than 4500 samples whole air samples collected over the remote Pacific Ocean during NASA's Global Tropospheric Experiment (GTE) Pacific Exploratory Mission-Tropics B (PEM-Tropics B) in March and early April 1999. Approximately 140 samples during a typical 8-hour DC-8 flight, and 120 canisters for each 8-hour flight aboard the P-3B. These samples were obtained roughly every 3-7 min during horizontal flight legs and 1-3 min during vertical legs. The filled canisters were analyzed in the laboratory at UCI within ten days of collection. The mixing ratios of 58 trace gases comprising hydrocarbons, halocarbons, alkyl nitrates and DMS were reported (and archived) for each sample. Two identical analytical systems sharing the same standards were operated simultaneously around the clock to improve canister turn-around time and to keep our measurement precision optimal. This report presents a summary of the results for sample collected.