Browsing by Author "Apel, Eric C."
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Item Airborne measurements of BrO and the sum of HOBr and Br2 over the Tropical West Pacific from 1 to 15 km during the CONvective TRansport of Active Species in the Tropics (CONTRAST) experiment(AGU Pubication, 2016-10-13) Chen, Dexian; Huey, L. Gregory; Tanner, David J.; Salawitch, Ross J.; Anderson, Daniel C.; Wales, Pamela A.; Pan, Laura L.; Atlas, Elliot L.; Hornbrook, Rebecca S.; Apel, Eric C.; Blake, Nicola J.; Campos, Teresa L.; Donets, Valeria; Flocke, Frank M.; Hall, Samuel R.; Hanisco, Thomas F.; Hills, Alan J.; Honomichl, Shawn B.; Jensen, Jørgen B.; Kaser, Lisa; Montzka, Denise D.; Nicely, Julie M; Reeves, Michael J.; Riemer, Daniel D.; Schauffler, Sue M.; Ullmann, Kirk; Weinheimer, Andrew J.; Wolfe, Glenn M.A chemical ionization mass spectrometer was used to measure BrO and HOBr + Br₂ over the Tropical West Pacific Ocean within the altitude range of 1 to 15 km, during the CONvective TRansport of Active Species in the Tropics (CONTRAST) campaign in 2014. Isolated episodes of elevated BrO (up to 6.6 pptv) and/or HOBr + Br₂ (up to 7.3 pptv) were observed in the tropical free troposphere (TFT) and were associated with biomass burning. However, most of the time we did not observe significant BrO or HOBr + Br₂ in the TFT and the tropical tropopause layer (TTL) above our limits of detection (LOD). The 1 min average LOD for BrO ranged from 0.6 to 1.6 pptv and for HOBr + Br₂ ranged from 1.3 to 3.5 pptv. During one flight, BrO observations from the TTL to the extratropical lowermost stratosphere were used to infer a profile of inorganic bromine (Bry). Based on this profile, we estimated the product gas injection of bromine species into the stratosphere to be 2 pptv. Analysis of Bry partitioning further indicates that BrO levels are likely very low in the TFT environment and that future studies should target the measurement of HBr or atomic Br.Item Atmospheric Acetaldehyde: Importance of Air‐Sea Exchange and a Missing Source in the Remote Troposphere(American Geophysical Union, 2019-05-28) Wang, Siyuan; Hornbrook, Rebecca S.; Hills, Alan; Emmons, Louisa K.; Tilmes, Simone; Lamarque, Jean‐François; Jimenez, Jose L.; Campuzano‐Jost, Pedro; Nault, Benjamin A.; Crounse, John D.; Wennberg, Paul O.; Kim, Michelle; Allen, Hannah; Ryerson, Thomas B.; Thompson, Chelsea R.; Peischl, Jeff; Moore, Fred; Nance, David; Hall, Brad; Elkins, James; Tanner, David; Huey, L. Gregory; Hall, Samuel R.; Ullmann, Kirk; Orlando, John J.; Tyndall, Geoff S.; Flocke, Frank M.; Ray, Eric; Hanisco, Thomas F.; Wolfe, Glenn M.; St. Clair, Jason; Commane, Róisín; Daube, Bruce; Barletta, Barbara; Blake, Donald R.; Weinzierl, Bernadett; Dollner, Maximilian; Conley, Andrew; Vitt, Francis; Wofsy, Steven C.; Riemer, Daniel D.; Apel, Eric C.We report airborne measurements of acetaldehyde (CH₃CHO) during the first and second deployments of the National Aeronautics and Space Administration Atmospheric Tomography Mission (ATom). The budget of CH₃CHO is examined using the Community Atmospheric Model with chemistry (CAM‐chem), with a newly developed online air‐sea exchange module. The upper limit of the global ocean net emission of CH₃CHO is estimated to be 34 Tg/a (42 Tg/a if considering bubble‐mediated transfer), and the ocean impacts on tropospheric CH₃CHO are mostly confined to the marine boundary layer. Our analysis suggests that there is an unaccounted CH₃CHO source in the remote troposphere and that organic aerosols can only provide a fraction of this missing source. We propose that peroxyacetic acid is an ideal indicator of the rapid CH₃CHO production in the remote troposphere. The higher‐than‐expected CH₃CHO measurements represent a missing sink of hydroxyl radicals (and halogen radical) in current chemistry‐climate models. Plain Language Summary The Earth's atmosphere and its ability to self‐regulate and cleanse itself is dependent on a complex interplay of trace chemical species, some of which are emitted from the biosphere, while others are from human activities or fires. One of these key species, acetaldehyde, was measured as part of the recent Atmospheric Tomography Mission, an aircraft (National Aeronautics and Space Administration DC‐8) experiment transecting the lengths of the Pacific and Atlantic Oceans during two seasons, measuring greenhouse gases and chemically reactive gases and particles. These measurements allow us to test our ability to model the chemical state of the atmosphere. The results indicate that the ocean is a large source of acetaldehyde and the analysis here suggests additional mechanisms that narrow the gap between observations and simulations but also reveal that an additional unexplained source or sources remain(s) in the remote free troposphere. It is critical to understand this missing carbon source because it has significant implications for understanding the cycle of oxidants which, in turn, provide for the means of removing (cleaning) trace gases including methane, an important greenhouse gas, from the atmosphere.Item BrO and inferred Bry profiles over the western Pacific: relevance of inorganic bromine sources and a Bry minimum in the aged tropical tropopause layer(Copernicus Publications, 2017-12-22) Koenig, Theodore K.; Volkamer, Rainer; Baidar, Sunil; Dix, Barbara; Wang, Siyuan; Anderson, Daniel C.; Salawitch, Ross J.; Wales, Pamela A.; Cuevas, Carlos A.; Fernandez, Rafael P.; Saiz‐Lopez, Alfonso; Evans, Matthew J.; Sherwen, Tomás; Jacob, Daniel J.; Schmidt, Johan; Kinnison, Douglas; Lamarque, Jean-François; Apel, Eric C.; Bresch, James C.; Campos, Teresa; Flocke, Frank M.; Hall, Samuel R.; Honomichl, Shawn B.; Hornbrook, Rebecca; Jensen, Jørgen B.; Lueb, Richard; Montzka, Denise D.; Pan, Laura L.; Reeves, J. Michael; Schauffler, Sue M.; Ullmann, Kirk; Weinheimer, Andrew J.; Atlas, Elliot L.; Donets, Valeria; Navarro, Maria A.; Riemer, Daniel; Blake, Nicola J.; Chen, Dexian; Huey, L. Gregory; Tanner, David J.; Hanisco, Thomas F.; Wolfe, Glenn M.We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box model to infer total gas-phase inorganic bromine (Bry) over the tropical western Pacific Ocean (tWPO) during the CONTRAST field campaign (January–February 2014). The observed BrO and inferred Bry profiles peak in the marine boundary layer (MBL), suggesting the need for a bromine source from sea-salt aerosol (SSA), in addition to organic bromine (CBry). Both profiles are found to be C-shaped with local maxima in the upper free troposphere (FT). The median tropospheric BrO vertical column density (VCD) was measured as 1.6×10¹³ molec cm⁻², compared to model predictions of 0.9×10¹³ molec cm⁻² in GEOS-Chem (CBry but no SSA source), 0.4×10¹³ molec cm⁻² in CAM-Chem (CBry and SSA), and 2.1×10¹³ molec cm⁻² in GEOS-Chem (CBry and SSA). Neither global model fully captures the C-shape of the Bry profile. A local Bry maximum of 3.6 ppt (2.9–4.4 ppt; 95 % confidence interval, CI) is inferred between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective tropical tropopause layer (TTL) to the aged TTL, gas-phase Bry decreases from the convective TTL to the aged TTL. Analysis of gas-phase Bry against multiple tracers (CFC-11, H₂O ∕ O₃ ratio, and potential temperature) reveals a Bry minimum of 2.7 ppt (2.3–3.1 ppt; 95 % CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6 ± 0.6 ppt of inorganic Bry (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.6–7.0 ppt; 95 % CI) in the stratospheric "middleworld" and 6.9 ppt (6.5–7.3 ppt; 95 % CI) in the stratospheric "overworld". The local Bry minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-Chem, and suggests a more complex partitioning of gas-phase and aerosol Bry species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA-derived gas-phase Bry) are needed to explain the gas-phase Bry budget in the upper free troposphere and TTL. They are also consistent with observations of significant bromide in Upper Troposphere–Lower Stratosphere aerosols. The total Bry budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas-phase Bry species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. Such simultaneous measurements are needed to (1) quantify SSA-derived Bry in the upper FT, (2) test Bry partitioning, and possibly explain the gas-phase Bry minimum in the aged TTL, (3) constrain heterogeneous reaction rates of bromine, and (4) account for all of the sources of BryItem Constraining remote oxidation capacity with ATom observations(Copernicus Publications, 2020-07-03) Travis, Katherine R.; Heald, Colette L.; Allen, Hannah M.; Apel, Eric C.; Arnold, Stephen R.; Blake, Donald R.; Brune, William H.; Chen, Xin; Commane, Róisín; Crounse, John D.; Daube, Bruce C.; Diskin, Glenn S.; Elkins, James W.; Evans, Mathew J.; Hall, Samuel R.; Hintsa, Eric J.; Hornbrook, Rebecca S.; Kasibhatla, Prasad S.; Kim, Michelle J.; Luo, Gan; McKain, Kathryn; Millet, Dylan B.; Moore, Fred L.; Peischl, Jeffrey; Ryerson, Thomas B.; Sherwen, Tomás; Thames, Alexander B.; Ullmann, Kirk; Wang, Xuan; Wennberg, Paul O.; Wolfe, Glenn; Yu, FangqunThe global oxidation capacity, defined as the tropospheric mean concentration of the hydroxyl radical (OH), controls the lifetime of reactive trace gases in the atmosphere such as methane and carbon monoxide (CO). Models tend to underestimate the methane lifetime and CO concentrations throughout the troposphere, which is consistent with excessive OH. Approximately half of the oxidation of methane and non-methane volatile organic compounds (VOCs) is thought to occur over the oceans where oxidant chemistry has received little validation due to a lack of observational constraints. We use observations from the first two deployments of the NASA ATom aircraft campaign during July–August 2016 and January–February 2017 to evaluate the oxidation capacity over the remote oceans and its representation by the GEOS-Chem chemical transport model. The model successfully simulates the magnitude and vertical profile of remote OH within the measurement uncertainties. Comparisons against the drivers of OH production (water vapor, ozone, and NOy concentrations, ozone photolysis frequencies) also show minimal bias, with the exception of wintertime NOy. The severe model overestimate of NOy during this period may indicate insufficient wet scavenging and/or missing loss on sea-salt aerosols. Large uncertainties in these processes require further study to improve simulated NOy partitioning and removal in the troposphere, but preliminary tests suggest that their overall impact could marginally reduce the model bias in tropospheric OH. During the ATom-1 deployment, OH reactivity (OHR) below 3 km is significantly enhanced, and this is not captured by the sum of its measured components (cOHRobs) or by the model (cOHRmod). This enhancement could suggest missing reactive VOCs but cannot be explained by a comprehensive simulation of both biotic and abiotic ocean sources of VOCs. Additional sources of VOC reactivity in this region are difficult to reconcile with the full suite of ATom measurement constraints. The model generally reproduces the magnitude and seasonality of cOHRobs but underestimates the contribution of oxygenated VOCs, mainly acetaldehyde, which is severely underestimated throughout the troposphere despite its calculated lifetime of less than a day. Missing model acetaldehyde in previous studies was attributed to measurement uncertainties that have been largely resolved. Observations of peroxyacetic acid (PAA) provide new support for remote levels of acetaldehyde. The underestimate in both model acetaldehyde and PAA is present throughout the year in both hemispheres and peaks during Northern Hemisphere summer. The addition of ocean sources of VOCs in the model increases cOHRmod by 3 % to 9 % and improves model–measurement agreement for acetaldehyde, particularly in winter, but cannot resolve the model summertime bias. Doing so would require 100 Tg yr⁻¹ of a long-lived unknown precursor throughout the year with significant additional emissions in the Northern Hemisphere summer. Improving the model bias for remote acetaldehyde and PAA is unlikely to fully resolve previously reported model global biases in OH and methane lifetime, suggesting that future work should examine the sources and sinks of OH over land.Item Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM‐Chem and the CCMI Models(AGU Pubication, 2017-10-06) Anderson, Daniel C.; Nicely, Julie M.; Wolfe, Glenn M.; Hanisco, Thomas F.; Salawitch, Ross J.; Canty, Timothy P.; Dickerson, Russell R.; Apel, Eric C.; Baidar, Sunil; Bannan, Thomas J.; Blake, Nicola J.; Chen, Dexian; Dix, Barbara; Fernandez, Rafael P.; Hall, Samuel R.; Hornbrook, Rebecca S.; Huey, L. Gregory; Josse, Beatrice; Jöckel, Patrick; Kinnison, Douglas E.; Koenig, Theodore K.; Breton, Michael Le; Marécal, Virginie; Morgenstern, Olaf; Oman, Luke D.; Pan, Laura L.; Percival, Carl; Plummer, David; Revell, Laura E.; Rozanov, Eugene; Saiz‐Lopez, Alfonso; Stenke, Andrea; Sudo, Kengo; Tilmes, Simone; Ullmann, Kirk; Volkamer, Rainer; Weinheimer, Andrew J.; Zeng, GuangFormaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HOx. In remote marine environments, such as the tropical western Pacific (TWP), it is particularly important to understand the processes controlling the abundance of HCHO because model output from these regions is used to correct satellite retrievals of HCHO. Here we have used observations from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, conducted during January and February 2014, to evaluate our understanding of the processes controlling the distribution of HCHO in the TWP as well as its representation in chemical transport/climate models. Observed HCHO mixing ratios varied from ~500 parts per trillion by volume (pptv) near the surface to ~75 pptv in the upper troposphere. Recent convective transport of near surface HCHO and its precursors, acetaldehyde and possibly methyl hydroperoxide, increased upper tropospheric HCHO mixing ratios by ~33% (22 pptv); this air contained roughly 60% less NO than more aged air. Output from the CAM‐Chem chemistry transport model (2014 meteorology) as well as nine chemistry climate models from the Chemistry‐Climate Model Initiative (free‐running meteorology) are found to uniformly underestimate HCHO columns derived from in situ observations by between 4 and 50%. This underestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NOx emissions inventories and/or in the model chemical mechanisms. Likewise, the lack of oceanic acetaldehyde emissions and potential errors in the model acetaldehyde chemistry lead to additional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere.Item Global airborne sampling reveals a previously unobserved dimethyl sulfide oxidation mechanism in the marine atmosphere(PNAS, 2020-02-18) Veres, Patrick R.; Neuman, J. Andrew; Bertman, Timothy H.; Assaf, Emmanuel; Wolfe, Glenn M.; Williamson, Christina J.; Weinzierl, Bernadett; Tilmes, Simone; Thompson, Chelsea R.; Thames, Alexander B.; Schroder, Jason C.; Saiz‐Lopez, Alfonso; Rollins, Andrew W.; Roberts, James M.; Price, Derek; Peischl, Jeff; Nault, Benjamin A.; Møller, Kristian H.; Miller, David O.; Meinardi, Simone; Li, Qinyi; Lamarque, Jean-François; Kupc, Agnieszka; Kjaergaard, Henrik G.; Kinnison, Douglas; Jimenez, Jose L.; Jernigan, Christopher M.; Hornbrook, Rebecca S.; Hills, Alan; Dollner, Maximilian; Day, Douglas A.; Cuevas, Carlos A.; Campuzano-Jost, Pedro; Burkholder, James; Bui, T. Paul; Brune, William H.; Brown, Steven S.; Brock, Charles A.; Bourgeois, Ilann; Blake, Donald R.; Apel, Eric C.; Ryerson, Thomas B.Dimethyl sulfide (DMS), emitted from the oceans, is the most abundant biological source of sulfur to the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect Earth’s radiative balance by scattering solar radiation and serving as cloud condensation nuclei. We report the atmospheric discovery of a previously unquantified DMS oxidation product, hydroperoxymethyl thioformate (HPMTF, HOOCH₂SCHO), identified through global-scale airborne observations that demonstrate it to be a major reservoir of marine sulfur. Observationally constrained model results show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth. Analyses of these observations show that HPMTF chemistry must be included in atmospheric models to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.Item Missing OH reactivity in the global marine boundary layer(Copernicus Publications, 2020-04-02) Thames, Alexander B.; Brune, William H.; Miller, David O.; Allen, Hannah M.; Apel, Eric C.; Blake, Donald R.; Bui, T. Paul; Commane, Roisin; Crounse, John D.; Daube, Bruce C.; Diskin, Glenn S.; DiGangi, Joshua P.; Elkins, James W.; Hall, Samuel R.; Hanisco, Thomas F.; Hannun, Reem; Hintsa, Eric; Hornbrook, Rebecca S.; Kim, Michelle J.; McKain, Kathryn; Moore, Fred L.; Nicely, Julie M.; Peischl, Jeffrey; Ryerson, Thomas B.; St. Clair, Jason; Sweeney, Colm; Teng, Alex; Thompson, Chelsea R.; Ullmann, Kirk; Wennberg, Paul O.; Wolfe, GlennThe hydroxyl radical (OH) reacts with thousands of chemical species in the atmosphere, initiating their removal and the chemical reaction sequences that produce ozone, secondary aerosols, and gas-phase acids. OH reactivity, which is the inverse of OH lifetime, influences the OH abundance and the ability of OH to cleanse the atmosphere. The NASA Atmospheric Tomography (ATom) campaign used instruments on the NASA DC-8 aircraft to measure OH reactivity and more than 100 trace chemical species. ATom presented a unique opportunity to test the completeness of the OH reactivity calculated from the chemical species measurements by comparing it to the measured OH reactivity over two oceans across four seasons. Although the calculated OH reactivity was below the limit of detection for the ATom instrument used to measure OH reactivity throughout much of the free troposphere, the instrument was able to measure the OH reactivity in and just above the marine boundary layer. The mean measured value of OH reactivity in the marine boundary layer across all latitudes and all ATom deployments was 1.9 s⁻¹, which is 0.5 s⁻¹ larger than the mean calculated OH reactivity. The missing OH reactivity, the difference between the measured and calculated OH reactivity, varied between 0 and 3.5 s⁻¹, with the highest values over the Northern Hemisphere Pacific Ocean. Correlations of missing OH reactivity with formaldehyde, dimethyl sulfide, butanal, and sea surface temperature suggest the presence of unmeasured or unknown volatile organic compounds or oxygenated volatile organic compounds associated with ocean emissions.Item An observationally constrained evaluation of the oxidative capacity in the tropical western Pacific troposphere(AGU Pubication, 2016-06-05) Nicely, Julie M; Anderson, Daniel C.; Canty, Timothy P.; Salawitch, Ross J.; Wolfe, Glenn M.; Apel, Eric C.; Arnold, Steve R.; Atlas, Elliot L.; Blake, Nicola J.; Bresch, James F.; Campos, Teresa L.; Dickerson, Russell R.; Duncan, Bryan; Emmons, Louisa K.; Evans, Matthew J.; Fernandez, Rafael P.; Flemming, Johannes; Hall, Samuel R.; Hanisco, Thomas F.; Honomichl, Shawn B.; Hornbrook, Rebecca S.; Huijnen, Vincent; Kaser, Lisa; Kinnison, Douglas E.; Lamarque, Jean‐Francois; Mao, Jingqiu; Monks, Sarah A.; Montzka, Denise D.; Pan, Laura L.; Riemer, Daniel D.; Saiz‐Lopez, Alfonso; Steenrod, Stephen D.; H. Stell, Meghan; Tilmes, Simone; Turquety, Solene; Ullmann, Kirk; Weinheimer, Andrew J.Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O₃, H₂O, NO, and other species from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, which occurred in the tropical western Pacific (TWP) during January–February 2014, to constrain a photochemical box model and estimate concentrations of OH throughout the troposphere. We find that tropospheric column OH (OHCOL) inferred from CONTRAST observations is 12 to 40% higher than found in chemical transport models (CTMs), including CAM‐chem‐SD run with 2014 meteorology as well as eight models that participated in POLMIP (2008 meteorology). Part of this discrepancy is due to a clear‐sky sampling bias that affects CONTRAST observations; accounting for this bias and also for a small difference in chemical mechanism results in our empirically based value of OHCOL being 0 to 20% larger than found within global models. While these global models simulate observed O₃ reasonably well, they underestimate NOx (NO + NO₂) by a factor of 2, resulting in OHCOL ~30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH₃CHO throughout the troposphere and of HCHO in the upper troposphere further contribute to differences between our constrained estimates of OH and those calculated by CTMs. Finally, our calculations do not support the prior suggestion of the existence of a tropospheric OH minimum in the TWP, because during January–February 2014 observed levels of O₃ and NO were considerably larger than previously reported values in the TWP.Item A pervasive role for biomass burning in tropical high ozone/low water structures(Nature Research, 2016-01-13) Anderson, Daniel C.; Nicely, Julie M.; Salawitch, Ross J.; Canty, Timothy P.; Dickerson, Russell R.; Hanisco, Thomas F.; Wolfe, Glenn M.; Apel, Eric C.; Atlas, Elliot; Bannan, Thomas; Bauguitte, Stephane; Blake, Nicola J.; Bresch, James F.; Campos, Teresa L.; Carpenter, Lucy J.; Cohen, Mark D.; Evans, Matthew; Fernandez, Rafael P.; Kahn, Brian H.; Kinnison, Douglas E.; Hall, Samuel R.; Harris, Neil R.P.; Hornbrook, Rebecca S.; Lamarque, Jean-Francois; Breton, Michael Le; Lee, James D.; Percival, Carl; Pfister, Leonhard; Pierce, R. Bradley; Riemer, Daniel D.; Saiz-Lopez, Alfonso; Stunder, Barbara J.B.; Thompson, Anne M.; Ullmann, Kirk; Vaughan, Adam; Weinheimer, Andrew J.Air parcels with mixing ratios of high O₃ and low H₂O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa). Here, using data collected during aircraft sampling of the TWP in winter 2014, we find strong, positive correlations of O₃ with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O₃ and that low H₂O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.Item Source and variability of formaldehyde (HCHO) at northern high latitude: an integrated satellite, aircraft, and model study(Copernicus Publications, 2022-06-03) Zhao, Tianlang; Mao, Jingqiu; Simpson, William R.; Smedt, Isabelle De; Zhu, Lei; Hanisco, Thomas F.; Wolfe, Glenn; Clair, Jason St.; Abad, Gonzalo González; Nowlan, Caroline R.; Barletta, Barbara; Meinardi, Simone; Blake, Donald R.; Apel, Eric C.; Hornbrook, Rebecca S.Here we use satellite observations of HCHO vertical column densities (VCD) from the TROPOspheric Monitoring Instrument (TROPOMI), ground-based and aircraft measurements, combined with a nested regional chemical transport model (GEOS-Chem at 0.5° × 0.625° resolution), to understand the variability and sources of summertime HCHO better in Alaska. We first evaluate GEOS-Chem with in-situ airborne measurements during Atmospheric Tomography Mission 1 (ATom-1) aircraft campaign and ground-based measurements from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS). We show reasonable agreement between observed and modeled HCHO, isoprene and monoterpenes. In particular, HCHO profiles show spatial homogeneity in Alaska, suggesting a minor contribution of biogenic emissions to HCHO VCD. We further examine the TROPOMI HCHO product in Alaska during boreal summer, which is in good agreement with GEOS-Chem model results. We find that HCHO VCDs are dominated by free-tropospheric background in wildfire-free regions. During the summer of 2018, the model suggests that the background HCHO column, resulting from methane oxidation, contributes to 66–80 % of the HCHO VCD, while wildfires contribute to 14 % and biogenic VOC contributes to 5–9 % respectively. For the summer of 2019, which had intense wildfires, the model suggests that wildfires contribute to 40 to 65 %, and the background column accounts for 30 to 50 % of HCHO VCD in June and July. In particular, the model indicates a major contribution of wildfires from direct emissions of HCHO, instead of secondary production of HCHO from oxidation of larger VOCs. We find that the column contributed by biogenic VOC is often small and below the TROPOMI detection limit. The source and variability of HCHO VCD above Alaska during summer is mainly driven by background methane oxidation and wildfires. This work discusses challenges for quantifying HCHO and its precursors in remote pristine regions.Item Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns(Copernicus Publications, 2020-10-29) Zhu, Lei; Abad, Gonzalo González; Nowlan, Caroline R.; Miller, Christopher Chan; Chance, Kelly; Apel, Eric C.; DiGangi, Joshua P.; Fried, Alan; Hanisco, Thomas F.; Hornbrook, Rebecca S.; Hu, Lu; Kaiser, Jennifer; Keutsch, Frank N.; Permar, Wade; St. Clair, Jason; Wolfe, GlennFormaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates negative biases (−44.5 % to −21.7 %) under high-HCHO conditions, while it indicates high biases (+66.1 % to +112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priori vertical profiles are likely not the main driver of the biases. By providing quick assessment of systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.Item Wet scavenging of soluble gases in DC3 deep convective storms using WRF‐Chem simulations and aircraft observations(AGU Pubication, 2016-04-02) Bela, Megan M.; Barth, Mary C.; Toon, Owen B.; Fried, Alan; Homeyer, Cameron R.; Morrison, Hugh; Cummings, Kristin A.; Li, Yunyao; Pickering, Kenneth E.; Allen, Dale J.; Yang, Qing; Wennberg, Paul O.; Crounse, John D.; St. Clair, Jason; Teng, Alex P.; O'Sullivan, Daniel; Huey, L. Gregory; Chen, Dexian; Liu, Xiaoxi; Blake, Donald R.; Blake, Nicola J.; Apel, Eric C.; Hornbrook, Rebecca S.; Flocke, Frank; Campos, Teresa; Diskin, GlennWe examine wet scavenging of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. We conduct high‐resolution simulations with the Weather Research and Forecasting model with Chemistry (WRF‐Chem) of a severe storm in Oklahoma. The model represents well the storm location, size, and structure as compared with Next Generation Weather Radar reflectivity, and simulated CO transport is consistent with aircraft observations. Scavenging efficiencies (SEs) between inflow and outflow of soluble species are calculated from aircraft measurements and model simulations. Using a simple wet scavenging scheme, we simulate the SE of each soluble species within the error bars of the observations. The simulated SEs of all species except nitric acid (HNO₃) are highly sensitive to the values specified for the fractions retained in ice when cloud water freezes. To reproduce the observations, we must assume zero ice retention for formaldehyde (CH₂O) and hydrogen peroxide (H₂O₂) and complete retention for methyl hydrogen peroxide (CH₃OOH) and sulfur dioxide (SO₂), likely to compensate for the lack of aqueous chemistry in the model. We then compare scavenging efficiencies among storms that formed in Alabama and northeast Colorado and the Oklahoma storm. Significant differences in SEs are seen among storms and species. More scavenging of HNO₃ and less removal of CH₃OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Graupel is associated with mixed‐phase scavenging and lightning production of nitrogen oxides (NOₓ), processes that may explain the observed differences in HNO₃ and CH₃OOH scavenging.Item Wintertime Overnight NOx Removal in a Southeastern United States Coal‐fired Power Plant Plume: A Model for Understanding Winter NOx Processing and its Implications(AGU Pubication, 2018-01-05) Fibiger, Dorothy L.; McDuffie, Erin E.; Dubé, William P.; Aikin, Kenneth C.; Lopez‐Hilfiker, Felipe D.; Lee, Ben H.; Green, Jamie R.; Fiddler, Marc N.; Holloway, John S.; Ebben, Carlena; Sparks, Tamara L.; Wooldridge, Paul; Weinheimer, Andrew J.; Montzka, Denise D.; Apel, Eric C.; Hornbrook, Rebecca S.; Hills, Alan J.; Blake, Nicola J.; DiGangi, Josh P; Wolfe, Glenn M.; Bililign, Solomon; Cohen, Ronald C.; Thornton, Joel A.; Brown, Steven S.Nitric oxide (NO) is emitted in large quantities from coal‐burning power plants. During the day, the plumes from these sources are efficiently mixed into the boundary layer, while at night, they may remain concentrated due to limited vertical mixing during which they undergo horizontal fanning. At night, the degree to which NO is converted to HNO₃ and therefore unable to participate in next‐day ozone (O₃) formation depends on the mixing rate of the plume, the composition of power plant emissions, and the composition of the background atmosphere. In this study, we use observed plume intercepts from the Wintertime INvestigation of Transport, Emissions and Reactivity campaign to test sensitivity of overnight NOx removal to the N₂O₅ loss rate constant, plume mixing rate, background O₃, and background levels of volatile organic compounds using a 2‐D box model of power plant plume transport and chemistry. The factor that exerted the greatest control over NOx removal was the loss rate constant of N₂O₅. At the lowest observed N₂O₅ loss rate constant, no other combination of conditions converts more than 10% of the initial NOx to HNO₃. The other factors did not influence NOx removal to the same degree.f