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Laughner, J. L., G. C. Toon, D. Wunch, S. Roche, J. Mendonca, M. Kiel, C. M. Roehl, C. Petri, and P. O. Wennberg. "The Total Carbon Column Observing Network's GGG2020 Data Version." Earth Sys. Sci. Data, (in prep), in prep

Abstract

Laughner, J. L., S. Roche, M. Kiel, G. C. Toon, D. Wunch, B. C. Baier, S. Biraud, H. Chen, R. Kivi, T. Laemmel, K. McKain, P.-Y. Qu\'eh\'e, C. Rousogenous, B. B. Stephens, K. Walker, and P. O. Wennberg. "A new algorithm to generate a priori trace gas profiles for the GGG2020 retrieval algorithm." Atmos. Meas. Tech. Discuss., 2022, 1--41, doi: 10.5194/amt-2022-267, 2022

Abstract
Optimal estimation retrievals of trace gas total columns require prior vertical profiles of the gases retrieved to drive the forward model and ensure the retrieval problem is mathematically well-posed. For well-mixed gases, it is possible to derive accurate prior profiles using an algorithm that accounts for general patterns of atmospheric transport coupled with measured time series of the gases in questions. Here we describe the algorithm used to generate the prior profiles for GGG2020, a new version of the GGG retrieval that is used to analyze spectra from solar-viewing Fourier transform spectrometers, including the Total Carbon Column Observing Network (TCCON). A particular focus of this work is improving the description of CO2, CH4, N2O, HF, and CO in the stratosphere. We show that the revised priors agree well with independent in situ and space-based measurements and improve the total column retrievals.

MacDonald, C. G., J. L. Laughner , J. K. Hedelius, R. Nassar, J.-P. Mastrogiacomo, and D. Wunch. "Estimating Enhancement Ratios of Nitrogen Dioxide, Carbon Monoxide, and Carbon Dioxide using Satellite Observations." Atmos. Chem. Phys. Discuss., 2022, 1--30, doi: 10.5194/acp-2022-474, 2022

Abstract
Using co-located space-based measurements of carbon dioxide (CO2) from the Orbiting Carbon Observatory 2 and 3 (OCO-2/3) and carbon monoxide (CO) and nitrogen dioxide (NO2) from the Tropospheric Monitoring Instrument (TROPOMI), we calculate total column enhancements for observations influenced by anthropogenic emissions from urban regions relative to clean background values. We apply this method to observations taken over or downwind of 27 large (> 1 million population) urban areas from around the world. Enhancement ratios between species are calculated and compared to emission ratios derived from four globally gridded anthropogenic emission inventories. We find that these global inventories underestimate CO emissions in many North American and European cities relative to our observed enhancement ratios, while smaller differences were found for NO2 emissions. We further demonstrate that the calculation and intercomparison of enhancement ratios of multiple tracers can help to identify the underlying biases leading to disagreement between observations and inventories. Additionally, we use high-resolution CO2 inventories for two cities (Los Angeles and Indianapolis) to estimate emissions of CO and NO2 using our calculated enhancement ratios, and find good agreement with both a previous modelling study for the Los Angeles megacity and California Air Resource Board (CARB) inventory estimates.

Zhu, Q., J. L. Laughner , and R. C. Cohen. "Estimate of OH Trends over One Decade in North American Cities." PNAS, 119, e2117399119, doi: 10.1073/pnas.2117399119, 2022

Abstract
The hydroxyl radical (OH) is the most important oxidant on global and local scales in the troposphere. Urban OH controls the removal rate of primary pollutants and triggers the production of ozone. Interannual trends of OH in urban areas are not well documented or understood due to the short lifetime and high spatial heterogeneity of OH. We utilize machine learning with observational inputs emphasizing satellite remote sensing observations to predict surface OH in 49 North American cities from 2005 to 2014. We observe changes in the summertime OH over one decade, with wide variation among different cities. In 2014, compared to the summertime OH in 2005, 3 cities show a significant increase of OH, whereas, in 27 cities, OH decreases in 2014. The year-to-year variation of OH is mapped to the decline of the NO2 column. We conclude that these cities in this analysis are either in the NOx-limited regime or at the transition from a NOx suppressed regime to a NOx-limited regime. The result emphasizes that, in the future, controlling NOx emissions will be most effective in regulating the ozone pollution in these cities.

Zhu, Q., J. L. Laughner , and R. C. Cohen. "Combining Machine Learning and Satellite Observations to Predict Spatial and Temporal Variation of near Surface OH in North American Cities." Environ. Sci. Technol., doi: 10.1021/acs.est.1c05636, 2022

Abstract
The hydroxyl radical (OH) is the primary cleansing agent in the atmosphere. The abundance of OH in cities initiates the removal of local pollutants; therefore, it serves as the key species describing the urban chemical environment. We propose a machine learning (ML) approach as an efficient alternative to OH simulation using a computationally expensive chemical transport model. The ML model is trained on the parameters simulated from the WRF-Chem model, and it suggests that six predictive parameters are capable of explaining 76% of the OH variability. The parameters are the tropospheric NO2 column, the tropospheric HCHO column, J(O1D), H2O, temperature, and pressure. We then use observations of the tropospheric NO2 column and HCHO column from OMI as input to the ML model to enable measurement-based prediction of daily near surface OH at 1:30 pm local time across 49 North American cities over the course of 10 years between 2005 and 2014. The result is validated by comparing the OH predictions to measurements of isoprene, which has a source that is uncorrelated with OH and is removed rapidly and almost exclusively by OH in the daytime. We demonstrate that the predicted OH is, as expected, anticorrelated with isoprene. We also show that this ML model is consistent with our understanding of OH chemistry given the solely data-driven nature.

Laughner, J.L., J.L. Neu, D. Schimel, P.O. Wennberg, K. Barsanti, K.W. Bowman, A. Chatterjee, B.E. Croes, H.L. Fitzmaurice, D.K. Henze, J. Kim, E.A. Kort, Z. Liu, K. Miyazaki, A.J. Turner, S. Anenberg, J. Avise, H. Cao, D. Crisp, J. de Gouw, A. Eldering, J.C. Fyfe, D.L. Goldberg, K.R. Gurney, S. Hasheminassab, F. Hopkins, C.E. Ivey, D.B.A. Jones, J. Liu, N.S. Lovenduski, R.V. Martin, G.A. McKinley, L. Ott, B. Poulter, M. Ru, S.P. Sander, N. Swart, Y.L. Yung, and Z.-C. Zeng. "Societal shifts due to COVID-19 reveal large-scale complexities and feedbacks between atmospheric chemistry and climate change." PNAS, 118, e2109481118, doi: https://doi.org/10.1073/pnas.2109481118, 2021

Abstract
The COVID-19 global pandemic and associated government lockdowns dramatically altered human activity, providing a window into how changes in individual behavior, enacted en masse, impact atmospheric composition. The resulting reductions in anthropogenic activity represent an unprecedented event that yields a glimpse into a future where emissions to the atmosphere are reduced. Furthermore, the abrupt reduction in emissions during the lockdown periods led to clearly observable changes in atmospheric composition, which provide direct insight into feedbacks between the Earth system and human activity. While air pollutants and greenhouse gases share many common anthropogenic sources, there is a sharp difference in the response of their atmospheric concentrations to COVID-19 emissions changes, due in large part to their different lifetimes. Here, we discuss several key takeaways from modeling and observational studies. First, despite dramatic declines in mobility and associated vehicular emissions, the atmospheric growth rates of greenhouse gases were not slowed, in part due to decreased ocean uptake of CO2 and a likely increase in CH4 lifetime from reduced NOx emissions. Second, the response of O3 to decreased NOx emissions showed significant spatial and temporal variability, due to differing chemical regimes around the world. Finally, the overall response of atmospheric composition to emissions changes is heavily modulated by factors including carbon-cycle feedbacks to CH4 and CO2, background pollutant levels, the timing and location of emissions changes, and climate feedbacks on air quality, such as wildfires and the ozone climate penalty.

Roche, S., K. Strong, D. Wunch, J. Mendonca, C. Sweeny, B. Baier, S. C. Biraud, J. L. Laughner , G. Toon, and B. Connor. "Retrieval of atmospheric CO2 vertical profiles from ground-based near-infrared spectra." Atmos. Meas. Tech., 14, 3087--3118, doi: 10.5194/amt-14-3087-2021, 2021

Abstract
We evaluate vertical profile retrievals of CO2 from 0.02 cm−1 resolution ground-based near-infrared solar absorption spectra with the GFIT2 algorithm, using improved spectroscopic line lists and line shapes. With these improvements, CO2 profiles were obtained from sequential retrievals in five spectral windows with different vertical sensitivities using synthetic and real spectra. A sensitivity study using synthetic spectra shows that the leading source of uncertainty in the retrieved CO2 profiles is the error in the a priori temperature profile, even with 3-hourly reanalysis a priori profiles. A 2 ∘C error in the temperature profile in the lower troposphere between 0.6 and 0.85 atm causes deviations in the retrieved CO2 profiles that are larger than the typical vertical variations of CO2. To distinguish the effect of errors in the a priori meteorology and trace gas concentration profiles from those in the instrument alignment and spectroscopic parameters, we retrieve CO2 profiles from atmospheric spectra while using an a priori profile built from coincident AirCore, radiosonde, and surface in situ measurements at the Lamont, Oklahoma (USA), Total Carbon Column Observing Network station. In those cases, the deviations in retrieved CO2 profiles are also larger than typical vertical variations of CO2, suggesting that remaining errors in the forward model limit the accuracy of the retrieved profiles. Implementing a temperature retrieval or correction and quantifying and modeling an imperfect instrument alignment are critical to improve CO2 profile retrievals. Without significant advances in modeling imperfect instrument alignment, and improvements in the accuracy of the temperature profile, the CO2 profile retrieval with GFIT2 presents no clear advantage over scaling retrievals for the purpose of ascertaining the total column.

Müller, A., H. Tanimoto, T. Sugita, T. Machida, S. Nakaoka, P. K. Patra, J. Laughner , and D. Crisp. "New approach to evaluate satellite-derived XCO2 over oceans by integrating ship and aircraft observations." Atmospheric Chemistry and Physics, 21, 8255--8271, doi: 10.5194/acp-21-8255-2021, 2021

Abstract

Taylor, T. E., A. Eldering, A. Merrelli, M. Kiel, P. Somkuti, Ce. Cheng, R. Rosenberg, B. Fisher, D. Crisp, R. Basilio, M. Bennett, D. Cervantes, A. Chang, L. Dang, C. Frankenberg, V. R. Haemmerle, G. R. Keller, T. Kurosu, J. L. Laughner , R. Lee, Y. Marchetti, R. R. Nelson, C. W. O'Dell, G. Osterman, R. Pavlick, C. Roehl, R. Schneider, G. Spiers, C. To, C. Wells, P. O. Wennberg, A. Yelamanchili, and S. Yu. "OCO-3 early mission operations and initial (vEarly) XCO2 and SIF retrievals." Rem. Sens. Environ., 251, 112032, doi: 10.1016/j.rse.2020.112032, 2020

Abstract
NASA's Orbiting Carbon Observatory-3 (OCO-3) was installed on the International Space Station (ISS) on 10 May 2019. OCO-3 combines the flight spare spectrometer from the Orbiting Carbon Observatory-2 (OCO-2) mission, which has been in operation since 2014, with a new Pointing Mirror Assembly (PMA) that facilitates observations of non-nadir targets from the nadir-oriented ISS platform. The PMA is a new feature of OCO-3, which is being used to collect data in all science modes, including nadir (ND), sun-glint (GL), target (TG), and the new snapshot area mapping (SAM) mode. This work provides an initial assessment of the OCO-3 instrument and algorithm performance, highlighting results from the first 8 months of operations spanning August 2019 through March 2020. During the In-Orbit Checkout (IOC) phase, critical systems such as power and cooling were verified, after which the OCO-3 spectrometer and PMA were subjected to a series of rigorous tests. First light of the OCO-3 spectrometer was on 26 June 2019, with full science operations beginning on 6 August 2019. The OCO-3 spectrometer on-orbit performance is consistent with that seen during preflight testing. Signal to noise ratios are in the expected range needed for high quality retrievals of the column-averaged carbon dioxide (CO2) dry-air mole fraction (XCO2) and solar-induced chlorophyll fluorescence (SIF), which will be used to help quantify and constrain the global carbon cycle. The first public release of OCO-3 Level 2 (L2) data products, called “vEarly”, is being distributed by NASA's Goddard Earth Sciences Data and Information Services Center (GES DISC). The intent of the vEarly product is to evaluate early mission performance, facilitate comparisons with OCO-2 products, and identify key areas to improve for the next data release. The vEarly XCO2 exhibits a root-mean-squared-error (RMSE) of ≃ 1, 1, 2 ppm versus a truth proxy for nadir-land, TG&SAM, and glint-water observations, respectively. The vEarly SIF shows a correlation with OCO-2 measurements of >0.9 for highly coincident soundings. Overall, the Level 2 SIF and XCO2 products look very promising, with performance comparable to OCO-2. A follow-on version of the OCO-3 L2 product containing a number of refinements, e.g., instrument calibration, pointing accuracy, and retrieval algorithm tuning, is anticipated by early in 2021.

Lapierre, J., J. Laughner , J. Geddes, W. Koshack, R. Cohen, and S. Pusede. "Observing regional variability in lightning NO2 production rates." J. Geophys. Res. Atmos., 125, e2019JD031362, doi: 10.1029/2019JD031362, 2020

Abstract
Lightning is a large and variable source of nitrogen oxides (NOx ≡ NO + NO2) to the upper troposphere. Precise estimates of lightning NOx (LNOx) production rates are needed to constrain tropospheric oxidation chemistry; however, controls over LNOx variability are poorly understood. Here, we describe an observational analysis of variability in LNO2 with lightning type by exploiting U.S. regional differences in lightning characteristics in the Southeast, South Central, and North Central United States. We use satellite NO2 measurements from the Ozone Monitoring Instrument with Berkeley High Resolution vertical column densities, a combined lightning data set derived from the Earth Networks Total Lightning Network and National Lightning Detection Network (TM) measurements, and hourly winds from the European Centre for Medium‐Range Weather Forecasts climate reanalysis data set (ERA5) over May–August 2014–2015. We find evidence that cloud‐to‐ground (CG) strokes produce a factor of 9–11 more NO2 than intracloud (IC) strokes for storms with stroke rates of at least 2,800 strokes·cell−1·hr−1. We show that regional differences in LNO2 production rates are generally consistent with regional patterns CG and IC stroke frequency and stroke current density. A comparison of stroke‐based and flash‐based CG/IC LNO2 estimates suggests that CG LNO2 is potentially underestimated when derived with flash data due to the operational definition of CG lightning. We find that differences in peak current explain a large portion of CG/IC LNO2 variability, but that other factors must also be important, including minimum stroke rate. Because IC and CG strokes produce NOx in distinct areas of the atmosphere, we test the sensitivity of our results against the atmospheric NO2 vertical distribution assumed in the a priori profiles; we show that the relative CG to IC LNO2 was generally insensitive to the assumed NO2 vertical distribution.

Zhu, Q., J. L. Laughner , and R. C. Cohen. "Lightning NO2 simulation over the contiguous US and its effects on satellite NO2 retrievals." Atmos. Chem. Phys., 19, 13067--13078, doi: 10.5194/acp-19-13067-2019, 2019

Abstract
Lightning is an important NOx source representing ∼10 % of the global source of odd N and a much larger percentage in the upper troposphere. The poor understanding of spatial and temporal patterns of lightning contributes to a large uncertainty in understanding upper tropospheric chemistry. We implement a lightning parameterization using the product of convective available potential energy (CAPE) and convective precipitation rate (PR) coupled with the Kain–Fritsch convective scheme (KF/CAPE-PR) into the Weather Research and Forecasting-Chemistry (WRF-Chem) model. Compared to the cloud-top height (CTH) lightning parameterization combined with the Grell 3-D convective scheme (G3/CTH), we show that the switch of convective scheme improves the correlation of lightning flash density in the southeastern US from 0.30 to 0.67 when comparing against the Earth Networks Total Lightning Network; the switch of lightning parameterization contributes to the improvement of the correlation from 0.48 to 0.62 elsewhere in the US. The simulated NO2 profiles using the KF/CAPE-PR parameterization exhibit better agreement with aircraft observations in the middle and upper troposphere. Using a lightning NOx production rate of 500 mol NO flash−1, the a priori NO2 profile generated by the simulation with the KF/CAPE-PR parameterization reduces the air mass factor for NO2 retrievals by 16 % on average in the southeastern US in the late spring and early summer compared to simulations using the G3/CTH parameterization. This causes an average change in NO2 vertical column density 4 times higher than the average uncertainty.

Laughner, J. L. and R. C. Cohen. "Direct observation of changing NOx lifetime in North American cities." Science, 366, 723--727, doi: 10.1126/science.aax6832, 2019

Coverage in the media:

Abstract
NOx lifetime relates nonlinearly to its own concentration; therefore, by observing how NOx lifetime changes with changes in its concentration, inferences can be made about the dominant chemistry occurring in an urban plume. We used satellite observations of NO2 from a new high-resolution product to show that NOx lifetime in approximately 30 North American cities has changed between 2005 and 2014 in a manner consistent with our understanding of NOx chemistry.

Silvern, R. F., D. J. Jacob, L. J. Mickley, M. P. Sulprizio, K. R. Travis, E. A. Marais, R. C. Cohen, J. L. Laughner , S. Choi, J. Joiner, and L. N. Lamsal. "Using satellite observations of tropospheric NO2 columns to infer long-term trends in US NOx emissions: the importance of accounting for the free tropospheric NO2 background." Atmos. Chem. Phys., 19, 8863--8878, doi: 10.5194/acp-19-8863-2019, 2019

Abstract
The National Emission Inventory (NEI) of the US Environmental Protection Agency (EPA) reports a steady decrease in US NOx emissions over the 2005–2017 period at a rate of 0.1 Tg N a−1 (53 % decrease over the period), reflecting sustained efforts to improve air quality. Tropospheric NO2 columns observed by the satellite-based Ozone Monitoring Instrument (OMI) over the US show a steady decrease until 2009 but a flattening afterward, which has been attributed to a flattening of NOx emissions, contradicting the NEI. We show here that the steady 2005–2017 decrease in NOx emissions reported by the NEI is in fact largely consistent with observed network trends of surface NO2 and ozone concentrations. The OMI NO2 trend is instead similar to that observed for nitrate wet deposition fluxes, which is weaker than that for anthropogenic NOx emissions, due to a large and increasing relative contribution of non-anthropogenic background sources of NOx (mainly lightning and soils). This is confirmed by contrasting OMI NO2 trends in urban winter, where the background is low and OMI NO2 shows a 2005–2017 decrease consistent with the NEI, and rural summer, where the background is high and OMI NO2 shows no significant 2005–2017 trend. A GEOS-Chem model simulation driven by NEI emission trends for the 2005–2017 period reproduces these different trends, except for the post-2009 flattening of OMI NO2, which we attribute to a model underestimate of free tropospheric NO2. Better understanding is needed of the factors controlling free tropospheric NO2 in order to relate satellite observations of tropospheric NO2 columns to the underlying NOx emissions and their trends. Focusing on urban winter conditions in the satellite data minimizes the effect of this free tropospheric background.

Laughner, J. L., Q. Zhu, and R. Cohen. "Evaluation of version 3.0B of the BEHR OMI NO2 product." Atmos. Meas. Tech., 12, 129--146, doi: 10.5194/amt-12-129-2019, 2019

Abstract
Version 3.0B of the Berkeley High Resolution (BEHR) Ozone Monitoring Instrument (OMI) NO2 product is designed to accurately retrieve daily variation in the high-spatial-resolution mapping of tropospheric column NO2 over continental North America between 25 and 50∘ N. To assess the product, we compare against in situ aircraft profiles and Pandora vertical column densities (VCDs). We also compare the WRF-Chem simulation used to generate the a priori NO2 profiles against observations. We find that using daily NO2 profiles improves the VCDs retrieved in urban areas relative to low-resolution or monthly a priori NO2 profiles by amounts that are large compared to current uncertainties in NOx emissions and chemistry (of the order of 10 % to 30 %). Based on this analysis, we offer suggestions to consider when designing retrieval algorithms and validation procedures for upcoming geostationary satellites.

Laughner, J. L., Q. Zhu, and R. C. Cohen. "The Berkeley High Resolution Tropospheric NO2 Product." Earth System Science Data, 10, 2069--2095, doi: 10.5194/essd-10-2069-2018, 2018

Abstract
We describe upgrades to the Berkeley High Resolution (BEHR) NO2 satellite retrieval product. BEHR v3.0B builds on the NASA version 3 standard Ozone Monitoring Instrument (OMI) tropospheric NO2 product to provide a high spatial resolution product for a domain covering the continental United States and lower Canada that is consistent with daily variations in the 12 km a priori NO2 profiles. Other improvements to the BEHR v3.0 product include surface reflectance and elevation, and factors affecting the NO2 a priori profiles such as lightning and anthropogenic emissions. We describe the retrieval algorithm in detail and evaluate the impact of changes to the algorithm between v2.1C and v3.0B on the retrieved NO2 vertical column densities (VCDs). Not surprisingly, we find that, on average, the changes to the a priori NO2 profiles and the update to the new NASA slant column densities have the greatest impact on the retrieved VCDs. More significantly, we find that using daily a priori profiles results in greater average VCDs than using monthly profiles in regions and times with significant lightning activity. The BEHR product is available as four subproducts on the University of California DASH repository, using monthly a priori profiles at native OMI pixel resolution (https://doi.org/10.6078/D1N086) and regridded to 0.05° × 0.05° (https://doi.org/10.6078/D1RQ3G) and using daily a priori profiles at native OMI (https://doi.org/10.6078/D1WH41) and regridded (https://doi.org/10.6078/D12D5X) resolutions. The subproducts using monthly profiles are currently available from January 2005 to July 2017, and will be expanded to more recent years. The subproducts using daily profiles are currently available for years 2005–2010 and 2012–2014; 2011 and 2015 on will be added as the necessary input data are simulated for those years.

Silvern, R. F., D. J. Jacob, K. R. Travis, T. Sherwen, M. J. Evans, R. C. Cohen, J. L. Laughner , S. R. Hall, K. Ullmann, J. D. Crounse, P. O. Wennberg, J. Peischl, and I. B. Pollack. "Observed NO/NO2 Ratios in the Upper Troposphere Imply Errors in NO‐NO2‐O3 Cycling Kinetics or an Unaccounted NOx Reservoir." Geophys. Res. Lett., 45, 4466--4474, doi: 10.1029/2018GL077728, 2018

Abstract
Observations from the SEAC4RS aircraft campaign over the southeast United States in August–September 2013 show NO/NO2 concentration ratios in the upper troposphere that are approximately half of photochemical equilibrium values computed from Jet Propulsion Laboratory (JPL) kinetic data. One possible explanation is the presence of labile NOx reservoir species, presumably organic, decomposing thermally to NO2 in the instrument. The NO2 instrument corrects for this artifact from known labile HNO4 and CH3O2NO2 NOx reservoirs. To bridge the gap between measured and simulated NO2, additional unaccounted labile NOx reservoir species would have to be present at a mean concentration of ~40 ppt for the SEAC4RS conditions (compared with 197 ppt for NOx). An alternative explanation is error in the low‐temperature rate constant for the NO + O3 reaction (30% 1‐σ uncertainty in JPL at 240 K) and/or in the spectroscopic data for NO2 photolysis (20% 1‐σ uncertainty). Resolving this discrepancy is important for understanding global budgets of tropospheric oxidants and for interpreting satellite observations of tropospheric NO2 columns.

Laughner, J. L. and R. C. Cohen. "Quantification of the effect of modeled lightning NO2 on UV-visible air mass factors." Atmos. Meas. Tech., 10, 4403--4419, doi: 10.5194/amt-10-4403-2017, 2017

Abstract
Space-borne measurements of tropospheric nitrogen dioxide (NO2) columns are up to 10x more sensitive to upper tropospheric (UT) NO2 than near-surface NO2 over low-reflectivity surfaces. Here, we quantify the effect of adding simulated lightning NO2 to the a priori profiles for NO2 observations from the Ozone Monitoring Instrument (OMI) using modeled NO2 profiles from the Weather Research and Forecasting–Chemistry (WRF-Chem) model. With observed NO2 profiles from the Deep Convective Clouds and Chemistry (DC3) aircraft campaign as observational truth, we quantify the bias in the NO2 column that occurs when lightning NO2 is not accounted for in the a priori profiles. Focusing on late spring and early summer in the central and eastern United States, we find that a simulation without lightning NO2 underestimates the air mass factor (AMF) by 25 % on average for common summer OMI viewing geometry and 35 % for viewing geometries that will be encountered by geostationary satellites. Using a simulation with 500 to 665 mol NO flash−1 produces good agreement with observed NO2 profiles and reduces the bias in the AMF to  <  ±4 % for OMI viewing geometries. The bias is regionally dependent, with the strongest effects in the southeast United States (up to 80 %) and negligible effects in the central US. We also find that constraining WRF meteorology to a reanalysis dataset reduces lightning flash counts by a factor of 2 compared to an unconstrained run, most likely due to changes in the simulated water vapor profile.

Nault, B. A., J. L. Laughner , P. J. Wooldridge, J. D. Crounse, J. Dibb, G. Diskin, J. Peischl, J. R. Podolske, I. B. Pollack, T. B. Ryerson, E. Scheuer, P. O. Wennberg, and R. C. Cohen. "Lightning NOx Emissions: Reconciling Measured and Modeled Estimates With Updated NOx Chemistry." Geophys. Res. Lett., 44, 9479--9488, doi: 10.1002/2017GL074436, 2017

Abstract
Lightning is one of the most important sources of upper tropospheric NOx; however, there is a large spread in estimates of the global emission rates (2–8 Tg N yr−1). We combine upper tropospheric in situ observations from the Deep Convective Clouds and Chemistry (DC3) experiment and global satellite‐retrieved NO2 tropospheric column densities to constrain mean lightning NOx (LNOx) emissions per flash. Insights from DC3 indicate that the NOx lifetime is ~3 h in the region of outflow of thunderstorms, mainly due to production of methyl peroxy nitrate and alkyl and multifunctional nitrates. The lifetime then increases farther downwind from the region of outflow. Reinterpreting previous analyses using the 3 h lifetime reduces the spread among various methods that have been used to calculate mean LNOx emissions per flash and indicates a global LNOx emission rate of ~9 Tg N yr−1, a flux larger than the high end of recent estimates.

Laughner, J. L., A. Zare, and R. C. Cohen. "Effects of daily meteorology on the interpretation of space-based remote sensing of NO2." Atmos. Chem. Phys., 16, 15247--15264, doi: 10.5194/acp-16-15247-2016, 2016

Abstract
Retrievals of tropospheric NO2 columns from UV–visible observations of reflected sunlight require a priori vertical profiles to account for the variation in sensitivity of the observations to NO2 at different altitudes. These profiles vary in space and time but are usually approximated using models that do not resolve the full details of this variation. Currently, no operational retrieval simulates these a priori profiles at both high spatial and high temporal resolution. Here we examine the additional benefits of daily variations in a priori profiles for retrievals already simulating a priori NO2 profiles at sufficiently high spatial resolution to identify variations of NO2 within urban plumes. We show the effects of introducing daily variation into a priori profiles can be as large as 40 % and 3 × 1015 molec. cm−2 for an individual day and lead to corrections as large as −13 % for a monthly average in a case study of Atlanta, GA, USA. Additionally, we show that NOx emissions estimated from space-based remote sensing using daily, high-spatial-resolution a priori profiles are  ∼ 100 % greater than those of a retrieval using spatially coarse a priori profiles, and 26–40 % less than those of a retrieval using monthly averaged high-spatial-resolution profiles.

Travis, K. R., D. J. Jacob, J. A. Fisher, P. S. Kim, E. A. Marais, L. Zhu, K. Yu, C. C. Miller, R. M. Yantosca, M. P. Sulprizio, A. M. Thompson, P. O. Wennberg, J. D. Crounse, J. M. St. Clair, R. C. Cohen, J. L. Laughner , J. E. Dibb, S. R. Hall, K. Ullmann, G. M. Wolfe, I. B. Pollack, J. Peischl, J. A. Neuman, and X. Zhou. "Why do models overestimate surface ozone in the Southeast United States?." Atmos. Chem. Phys., 16, 13561--13577, doi: 10.5194/acp-16-13561-2016, 2016

Abstract
Ozone pollution in the Southeast US involves complex chemistry driven by emissions of anthropogenic nitrogen oxide radicals (NOx  ≡  NO + NO2) and biogenic isoprene. Model estimates of surface ozone concentrations tend to be biased high in the region and this is of concern for designing effective emission control strategies to meet air quality standards. We use detailed chemical observations from the SEAC4RS aircraft campaign in August and September 2013, interpreted with the GEOS-Chem chemical transport model at 0.25°  ×  0.3125° horizontal resolution, to better understand the factors controlling surface ozone in the Southeast US. We find that the National Emission Inventory (NEI) for NOx from the US Environmental Protection Agency (EPA) is too high. This finding is based on SEAC4RS observations of NOx and its oxidation products, surface network observations of nitrate wet deposition fluxes, and OMI satellite observations of tropospheric NO2 columns. Our results indicate that NEI NOx emissions from mobile and industrial sources must be reduced by 30–60 %, dependent on the assumption of the contribution by soil NOx emissions. Upper-tropospheric NO2 from lightning makes a large contribution to satellite observations of tropospheric NO2 that must be accounted for when using these data to estimate surface NOx emissions. We find that only half of isoprene oxidation proceeds by the high-NOx pathway to produce ozone; this fraction is only moderately sensitive to changes in NOx emissions because isoprene and NOx emissions are spatially segregated. GEOS-Chem with reduced NOx emissions provides an unbiased simulation of ozone observations from the aircraft and reproduces the observed ozone production efficiency in the boundary layer as derived from a regression of ozone and NOx oxidation products. However, the model is still biased high by 6 ± 14 ppb relative to observed surface ozone in the Southeast US. Ozonesondes launched during midday hours show a 7 ppb ozone decrease from 1.5 km to the surface that GEOS-Chem does not capture. This bias may reflect a combination of excessive vertical mixing and net ozone production in the model boundary layer.

Pusede, S. E., K. C. Duffey, A. A. Shusterman, A. Saleh, J. L. Laughner , P. J. Wooldridge, Q. Zhang, C. L. Parworth, H. Kim, S. L. Capps, L. C. Valin, C. D. Cappa, A. Fried, J. Walega, J. B. Nowak, A. J. Weinheimer, R. M. Hoff, T. A. Berkoff, A. J. Beyersdorf, J. Olson, J. H. Crawford, and R. C. Cohen. "On the effectiveness of nitrogen oxide reductions as a control over ammonium nitrate aerosol." Atmos. Chem. Phys., 16, 2575--2596, doi: 10.5194/acp-16-2575-2016, 2016

Abstract
Nitrogen oxides (NOx) have fallen steadily across the US over the last 15 years. At the same time, NOx concentrations decrease on weekends relative to weekdays, largely without co-occurring changes in other gas-phase emissions, due to patterns of diesel truck activities. These trends taken together provide two independent constraints on the role of NOx in the nonlinear chemistry of atmospheric oxidation. In this context, we interpret interannual trends in wintertime ammonium nitrate (NH4NO3) in the San Joaquin Valley of California, a location with the worst aerosol pollution in the US and where a large portion of aerosol mass is NH4NO3. Here, we show that NOx reductions have simultaneously decreased nighttime and increased daytime NH4NO3 production over the last decade. We find a substantial decrease in NH4NO3 since 2000 and conclude that this decrease is due to reduced nitrate radical-initiated production at night in residual layers that are decoupled from fresh emissions at the surface. Further reductions in NOx are imminent in California, and nationwide, and we make a quantitative prediction of the response of NH4NO3. We show that the combination of rapid chemical production and efficient NH4NO3 loss via deposition of gas-phase nitric acid implies that high aerosol days in cities in the San Joaquin Valley air basin are responsive to local changes in NOx within those individual cities. Our calculations indicate that large decreases in NOx in the future will not only lower wintertime NH4NO3 concentrations but also cause a transition in the dominant NH4NO3 source from nighttime to daytime chemistry.

Laughner, J. L.. "Virtual Evolving and Self-Producing Rapid Audio (V.E.S.P.R.A.)." Link, , 2013.

Abstract

Laughner, J. L.. "Synthesis and Transport Studies of a Delivery Mechanism for Oxidative in-situ Remediation of Groundwater." Link, , 2013.

Abstract