Browsing by Author "Kowalewski, Matthew G."
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Item Comprehensive evaluations of diurnal NO₂ measurements during DISCOVER-AQ 2011: effects of resolution-dependent representation of NOₓ emissions(EGU, 2021-07-23) Li, Jianfeng; Wang, Yuhang; Zhang, Ruixiong; Smeltzer, Charles; Weinheimer, Andrew; Herman, Jay; Boersma, K. Folkert; Celarier, Edward A.; Long, Russell W.; Szykman, James J.; Delgado, Ruben; Thompson, Anne M.; Knepp, Travis N.; Lamsal, Lok N.; Janz, Scott J.; Kowalewski, Matthew G.; Liu, Xiong; Nowlan, Caroline R.Nitrogen oxides (NOₓ = NO + NO₂) play a crucial role in the formation of ozone and secondary inorganic and organic aerosols, thus affecting human health, global radiation budget, and climate. The diurnal and spatial variations in NO₂ are functions of emissions, advection, deposition, vertical mixing, and chemistry. Their observations, therefore, provide useful constraints in our understanding of these factors. We employ a Regional chEmical and trAnsport model (REAM) to analyze the observed temporal (diurnal cycles) and spatial distributions of NO₂ concentrations and tropospheric vertical column densities (TVCDs) using aircraft in situ measurements and surface EPA Air Quality System (AQS) observations as well as the measurements of TVCDs by satellite instruments (OMI: the Ozone Monitoring Instrument; GOME-2A: Global Ozone Monitoring Experiment – 2A), ground-based Pandora, and the Airborne Compact Atmospheric Mapper (ACAM) instrument in July 2011 during the DISCOVER-AQ campaign over the Baltimore–Washington region. The model simulations at 36 and 4 km resolutions are in reasonably good agreement with the regional mean temporospatial NO₂ observations in the daytime. However, we find significant overestimations (underestimations) of model-simulated NO₂ (O₃) surface concentrations during nighttime, which can be mitigated by enhancing nocturnal vertical mixing in the model. Another discrepancy is that Pandora-measured NO₂ TVCDs show much less variation in the late afternoon than simulated in the model. The higher-resolution 4 km simulations tend to show larger biases compared to the observations due largely to the larger spatial variations in NOₓ emissions in the model when the model spatial resolution is increased from 36 to 4 km. OMI, GOME-2A, and the high-resolution aircraft ACAM observations show a more dispersed distribution of NO₂ vertical column densities (VCDs) and lower VCDs in urban regions than corresponding 36 and 4 km model simulations, likely reflecting the spatial distribution bias of NOₓ emissions in the National Emissions Inventory (NEI) 2011.Item Evaluating the impact of spatial resolution on tropospheric NO2 column comparisons within urban areas using high-resolution airborne data(EGU, 2019-11-22) Judd, Laura M.; Al-Saadi, Jassim A.; Janz, Scott J.; Kowalewski, Matthew G.; Pierce, R. Bradley; Szykman, James J.; Valin, Lukas C.; Swap, Robert; Cede, Alexander; Mueller, Moritz; Tiefengraber, Martin; Abuhassan, Nader; Williams, DavidNASA deployed the GeoTASO airborne UV–visible spectrometer in May–June 2017 to produce high-resolution (approximately 250 m×250 m) gapless NO₂ datasets over the western shore of Lake Michigan and over the Los Angeles Basin. The results collected show that the airborne tropospheric vertical column retrievals compare well with ground-based Pandora spectrometer column NO₂ observations (r²=0.91 and slope of 1.03). Apparent disagreements between the two measurements can be sensitive to the coincidence criteria and are often associated with large local variability, including rapid temporal changes and spatial heterogeneity that may be observed differently by the sunward-viewing Pandora observations. The gapless mapping strategy executed during the 2017 GeoTASO flights provides data suitable for averaging to coarser areal resolutions to simulate satellite retrievals. As simulated satellite pixel area increases to values typical of TEMPO (Tropospheric Emissions: Monitoring Pollution), TROPOMI (TROPOspheric Monitoring Instrument), and OMI (Ozone Monitoring Instrument), the agreement with Pandora measurements degraded, particularly for the most polluted columns as localized large pollution enhancements observed by Pandora and GeoTASO are spatially averaged with nearby less-polluted locations within the larger area representative of the satellite spatial resolutions (aircraft-to-Pandora slope: TEMPO scale =0.88; TROPOMI scale =0.77; OMI scale =0.57). In these two regions, Pandora and TEMPO or TROPOMI have the potential to compare well at least up to pollution scales of 30×10¹⁵ molecules cm⁻². Two publicly available OMI tropospheric NO₂ retrievals are found to be biased low with respect to these Pandora observations. However, the agreement improves when higher-resolution a priori inputs are used for the tropospheric air mass factor calculation (NASA V3 standard product slope =0.18 and Berkeley High Resolution product slope =0.30). Overall, this work explores best practices for satellite validation strategies with Pandora direct-sun observations by showing the sensitivity to product spatial resolution and demonstrating how the high-spatial-resolution NO₂ data retrieved from airborne spectrometers, such as GeoTASO, can be used with high-temporal-resolution ground-based column observations to evaluate the influence of spatial heterogeneity on validation results.Item First Top-Down Estimates of Anthropogenic NOxEmissions Using High-Resolution AirborneRemote Sensing Observations(AGU, 2018-03-07) Souri, Amir H.; Choi, Yunsoo; Pan, Shuai; Curci, Gabriele; Nowlan, Caroline R.; Janz, Scott J.; Kowalewski, Matthew G.; Liu, Junjie; Herman, Jay; Weinheimer, Andrew J.A number of satellite-based instruments have become an essential part of monitoring emissions.Despite sound theoretical inversion techniques, the insufficient samples and the footprint size of currentobservations have introduced an obstacle to narrow the inversion window for regional models. These keylimitations can be partially resolved by a set of modest high-quality measurements from airborne remotesensing. This study illustrates the feasibility of nitrogen dioxide (NO₂) columns from the Geostationary Coastal and Air Pollution Events Airborne Simulator (GCAS) to constrain anthropogenic NOx emissions in theHouston-Galveston-Brazoria area. We convert slant column densities to vertical columns using a radiativetransfer model with (i) NO₂ profiles from a high-resolution regional model (1 × 1 km²) constrained by P-3B aircraft measurements, (ii) the consideration of aerosol optical thickness impacts on radiance at NO₂ absorption line, and (iii) high-resolution surface albedo constrained by ground-based spectrometers. Wecharacterize errors in the GCAS NO₂ columns by comparing them to Pandora measurements andfind astriking correlation (r>0.74) with an uncertainty of 3.5 × 10¹⁵ molecules cm⁻². On 9 of 10 total days, the constrained anthropogenic emissions by a Kalmanfilter yield an overall 2–50% reduction in polluted areas,partly counterbalancing the well-documented positive bias of the model. The inversion, however, boostsemissions by 94% in the same areas on a day when an unprecedented local emissions event potentially occurred, significantly mitigating the bias of the model. The capability of GCAS at detecting such an event ensures the significance of forthcoming geostationary satellites for timely estimates of top-down emissions.Item Nitrogen dioxide and formaldehyde measurements from the GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator over Houston, Texas(EGU, 2018-10-30) Nowlan, Caroline R.; Liu, Xiong; Janz, Scott J.; Kowalewski, Matthew G.; Chance, Kelly; Follette-Cook, Melanie B.; Fried, Alan; Abad, Gonzalo González; Herman, Jay; Judd, Laura M.; Kwon, Hyeong-Ahn; Loughner, Christopher P.; Pickering, Kenneth E.; Richter, Dirk; Spinei, Elena; Walega, James; Weibring, Petter; Weinheimer, Andrew J.The GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was developed in support of NASA's decadal survey GEO-CAPE geostationary satellite mission. GCAS is an airborne push-broom remote-sensing instrument, consisting of two channels which make hyperspectral measurements in the ultraviolet/visible (optimized for air quality observations) and the visible–near infrared (optimized for ocean color observations). The GCAS instrument participated in its first intensive field campaign during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign in Texas in September 2013. During this campaign, the instrument flew on a King Air B-200 aircraft during 21 flights on 11 days to make air quality observations over Houston, Texas. We present GCAS trace gas retrievals of nitrogen dioxide (NO₂) and formaldehyde (CH₂O), and compare these results with trace gas columns derived from coincident in situ profile measurements of NO₂ and CH₂O made by instruments on a P-3B aircraft, and with NO₂ observations from ground-based Pandora spectrometers operating in direct-sun and scattered light modes. GCAS tropospheric column measurements correlate well spatially and temporally with columns estimated from the P-3B measurements for both NO₂ (r²=0.89) and CH₂O (r²=0.54) and with Pandora direct-sun (r²=0.85) and scattered light (r²=0.94) observed NO₂ columns. Coincident GCAS columns agree in magnitude with NO₂ and CH₂O P-3B-observed columns to within 10 % but are larger than scattered light Pandora tropospheric NO₂ columns by 33 % and direct-sun Pandora NO₂ columns by 50 %.