Publication Search Results

ID: 158179
Type: article
Authors: Choi, Haklim; Liu, Xiong; Gonzalez Abad, Gonzalo; Seo, Jongjin; Lee, Kwang-Mog; Kim, Jhoon
Abstract: Clouds act as a major reflector that changes the amount of sunlight reflected to space. Change in radiance intensity due to the presence of clouds interrupts the retrieval of trace gas or aerosol properties from satellite data. In this paper, we developed a fast and robust algorithm, named the fast cloud retrieval algorithm, using a triplet of wavelengths (469, 477, and 485 nm) of the O-2-O-2 absorption band around 477 nm (CLDTO4) to derive the cloud information such as cloud top pressure (CTP) and cloud fraction (CF) for the Geostationary Environment Monitoring Spectrometer (GEMS). The novel algorithm is based on the fact that the difference in the optical path through which light passes with regard to the altitude of clouds causes a change in radiance due to the absorption of O-2-O-2 at the three selected wavelengths. To reduce the time required for algorithm calculations, the look-up table (LUT) method was applied. The LUT was pre-constructed for various conditions of geometry using Vectorized Linearized Discrete Ordinate Radiative Transfer (VLIDORT) to consider the polarization of the scattered light. The GEMS was launched in February 2020, but the observed data of GEMS have not yet been widely released. To evaluate the performance of the algorithm, the retrieved CTP and CF using observational data from the Global Ozone Monitoring Experiment-2 (GOME-2), which cover the spectral range of GEMS, were compared with the results of the Fast Retrieval Scheme for Clouds from the Oxygen A band (FRESCO) algorithm, which is based on the O-2 A-band. There was good agreement between the results, despite small discrepancies for low clouds.

ID: 158802
Type: article
Authors: Judd, Laura M.; Al-Saadi, Jassim A.; Szykman, James J.; Valin, Lukas C.; Janz, Scott J.; Kowalewski, Matthew G.; Eskes, Henk J.; Pepijn Veefkind, J.; Cede, Alexander; Mueller, Moritz; Gebetsberger, Manuel; Swap, Robert; Pierce, R. Bradley; Nowlan, Caroline R.; González Abad, Gonzalo; Nehrir, Amin; Williams, David
Abstract: Airborne and ground-based Pandora spectrometer NO₂ column measurements were collected during the 2018 Long Island Sound Tropospheric Ozone Study (LISTOS) in the New York City/Long Island Sound region, which coincided with early observations from the Sentinel-5P TROPOspheric Monitoring Instrument (TROPOMI) instrument. Both airborne- and ground-based measurements are used to evaluate the TROPOMI NO₂ Tropospheric Vertical Column (TrVC) product v1.2 in this region, which has high spatial and temporal heterogeneity in NO₂. First, airborne and Pandora TrVCs are compared to evaluate the uncertainty of the airborne TrVC and establish the spatial representativeness of the Pandora observations. The 171 coincidences between Pandora and airborne TrVCs are found to be highly correlated (r²= 0.92 and slope of 1.03), with the largest individual differences being associated with high temporal and/or spatial variability. These reference measurements (Pandora and airborne) are complementary with respect to temporal coverage and spatial representativity. Pandora spectrometers can provide continuous long-term measurements but may lack areal representativity when operated in direct-sun mode. Airborne spectrometers are typically only deployed for short periods of time, but their observations are more spatially representative of the satellite measurements with the added capability of retrieving at subpixel resolutions of 250 m × 250 m over the entire TROPOMI pixels they overfly. Thus, airborne data are more correlated with TROPOMI measurements (r²=0.96) than Pandora measurements are with TROPOMI (r²=0.84). The largest outliers between TROPOMI and the reference measurements appear to stem from too spatially coarse a priori surface reflectivity (0.5^°) over bright urban scenes. In this work, this results during cloud-free scenes that, at times, are affected by errors in the TROPOMI cloud pressure retrieval impacting the calculation of tropospheric air mass factors. This factor causes a high bias in TROPOMI TrVCs of 4 %-11 %. Excluding these cloud-impacted points, TROPOMI has an overall low bias of 19 %-33 % during the LISTOS timeframe of June-September 2018. Part of this low bias is caused by coarse a priori profile input from the TM5-MP model; replacing these profiles with those from a 12 km North American Model-Community Multiscale Air Quality (NAMCMAQ) analysis results in a 12 %-14 % increase in the TrVCs. Even with this improvement, the TROPOMI-NAMCMAQ TrVCs have a 7 %-19 % low bias, indicating needed improvement in a priori assumptions in the air mass factor calculation. Future work should explore additional impacts of a priori inputs to further assess the remaining low biases in TROPOMI using these datasets.

ID: 155672
Type: article
Authors: Kim, Jhoon; Jeong, Ukkyo; Ahn, Myoung-Hwan; Kim, Jae H.; Park, Rokjin J.; Lee, Hanlim; Song, Chul Han; Choi, Yong-Sang; Lee, Kwon-Ho; Yoo, Jung-Moon; Jeong, Myeong-Jae; Park, Seon Ki; Lee, Kwang-Mog; Song, Chang-Keun; Kim, Sang-Woo; Kim, Young Joon; Kim, Si-Wan; Kim, Mijin; Go, Sujung; Liu, Xiong; Chance, Kelly; Chan Miller, Christopher; Al-Saadi, Jay; Veihelmann, Ben; Bhartia, Pawan K.; Torres, Omar; González-Abad, Gonzalo; Haffner, David P.; Ko, Dai Ho; Lee, Seung Hoon; Woo, Jung-Hun; Chong, Heesung; Park, Sang Seo; Nicks, Dennis; Choi, Won Jun; Moon, Kyung-Jung; Cho, Ara; Yoon, Jongmin; Kim, Sang-kyun; Hong, Hyunkee; Lee, Kyunghwa; Lee, Hana; Lee, Seoyoung; Choi, Myungje; Veefkind, Pepijn; Levelt, Pieternel F.; Edwards, David P.; Kang, Mina; Eo, Mijin; Bak, Juseon; Baek, Kanghyun; Kwon, Hyeong-Ahn; Yang, Jiwon; Park, Junsung; Han, Kyung Man; Kim, Bo-Ram; Shin, Hee-Woo; Choi, Haklim; Lee, Ebony; Chong, Jihyo; Cha, Yesol; Koo, Ja-Ho; Irie, Hitoshi; Hayashida, Sachiko; Kasai, Yasko; Kanaya, Yugo; Liu, Cheng; Lin, Jintai; Crawford, James H.; Carmichael, Gregory R.; Newchurch, Michael J.; Lefer, Barry L.; Herman, Jay R.; Swap, Robert J.; Lau, Alexis K. H.; Kurosu, Thomas P.; Jaross, Glen; Ahlers, Berit; Dobber, Marcel; McElroy, C. Thomas; Choi, Yunsoo
Abstract: The Geostationary Environment Monitoring Spectrometer (GEMS) is scheduled for launch in February 2020 to monitor air quality (AQ) at an unprecedented spatial and temporal resolution from a geostationary Earth orbit (GEO) for the first time. With the development of UV-visible spectrometers at sub-nm spectral resolution and sophisticated retrieval algorithms, estimates of the column amounts of atmospheric pollutants (O₃, NO₂, SO₂, HCHO, CHOCHO, and aerosols) can be obtained. To date, all the UV-visible satellite missions monitoring air quality have been in low Earth orbit (LEO), allowing one to two observations per day. With UV-visible instruments on GEO platforms, the diurnal variations of these pollutants can now be determined. Details of the GEMS mission are presented, including instrumentation, scientific algorithms, predicted performance, and applications for air quality forecasts through data assimilation. GEMS will be on board the Geostationary Korea Multi-Purpose Satellite 2 (GEO- KOMPSAT-2) satellite series, which also hosts the Advanced Meteorological Imager (AMI) and Geostationary Ocean Color Imager 2 (GOCI-2). These three instruments will provide synergistic science products to better understand air quality, meteorology, the long-range transport of air pollutants, emission source distributions, and chemical processes. Faster sampling rates at higher spatial resolution will increase the probability of finding cloud-free pixels, leading to more observations of aerosols and trace gases than is possible from LEO. GEMS will be joined by NASA's Tropospheric Emissions: Monitoring of Pollution (TEMPO) and ESA's Sentinel-4 to form a GEO AQ satellite constellation in early 2020s, coordinated by the Committee on Earth Observation Satellites (CEOS).

ID: 158080
Type: article
Authors: Souri, Amir H.; Nowlan, Caroline R.; González Abad, Gonzalo; Zhu, Lei; Blake, Donald R.; Fried, Alan; Weinheimer, Andrew J.; Wisthaler, Armin; Woo, Jung-Hun; Zhang, Qiang; Miller, Christopher E. Chan; Liu, Xiong; Chance, Kelly
Abstract: The absence of up-to-date emissions has been a major impediment to accurately simulating aspects of atmospheric chemistry and to precisely quantifying the impact of changes in emissions on air pollution. Hence, a nonlinear joint analytical inversion (Gauss-Newton method) of both volatile organic compounds (VOCs) and nitrogen oxide (NO_x) emissions is made by exploiting the Smithsonian Astrophysical Observatory (SAO) Ozone Mapping and Profiler Suite Nadir Mapper (OMPS-NM) formaldehyde (HCHO) and the National Aeronautics and Space Administration (NASA) Ozone Monitoring Instrument (OMI) tropospheric nitrogen dioxide (NO₂) columns during the Korea-United States Air Quality (KORUS-AQ) campaign over East Asia in May-June 2016. Effects of the chemical feedback of NO_x and VOCs on both NO₂ and HCHO are implicitly included by iteratively optimizing the inversion. Emission uncertainties are greatly narrowed (averaging kernels > 0.8, which is the mathematical presentation of the partition of information gained from the satellite observations with respect to the prior knowledge) over medium- to high-emitting areas such as cities and dense vegetation. The prior amount of total NO_x emissions is mainly dictated by values reported in the MIX-Asia 2010 inventory. After the inversion we conclude that there is a decline in emissions (before, after, change) for China (87.94±44.09 Gg d^-1, 68.00±15.94 Gg d^-1, -23 %), North China Plain (NCP) (27.96±13.49 Gg d^-1, 19.05±2.50 Gg d^-1, -32 %), Pearl River Delta (PRD) (4.23±1.78 Gg d^-1, 2.70±0.32 Gg d^-1, -36 %), Yangtze River Delta (YRD) (9.84±4.68 Gg d^-1, 5.77±0.51 Gg d^-1, -41 %), Taiwan (1.26±0.57 Gg d^-1, 0.97±0.33 Gg d^-1, -23 %), and Malaysia (2.89±2.77 Gg d^-1, 2.25±1.34 Gg d^-1, -22 %), all of which have effectively implemented various stringent regulations. In contrast, South Korea (2.71±1.34 Gg d^-1, 2.95±0.58 Gg d^-1, +9 %) and Japan (3.53±1.71 Gg d^-1, 3.96±1.04 Gg d^-1, +12 %) are experiencing an increase in NO_x emissions, potentially due to an increased number of diesel vehicles and new thermal power plants. We revisit the well-documented positive bias (by a factor of 2 to 3) of MEGAN v2.1 (Model of Emissions of Gases and Aerosols from Nature) in terms of biogenic VOC emissions in the tropics. The inversion, however, suggests a larger growth of VOCs (mainly anthropogenic) over NCP (25 %) than previously reported (6 %) relative to 2010. The spatial variation in both the magnitude and sign of NO_x and VOC emissions results in nonlinear responses of ozone production and loss. Due to a simultaneous decrease and increase in NO_x/VOC over NCP and YRD, we observe a ∼53 % reduction in the ratio of the chemical loss of NO_x (LNO_x) to the chemical loss of RO_x (RO₂+HO₂) over the surface transitioning toward NO_x-sensitive regimes, which in turn reduces and increases the afternoon chemical loss and production of ozone through NO₂+OH (-0.42 ppbv h^-1)/HO₂ (and RO₂)+NO (+0.31 ppbv h^-1). Conversely, a combined decrease in NO_x and VOC emissions in Taiwan, Malaysia, and southern China suppresses the formation of ozone. Simulations using the updated emissions indicate increases in maximum daily 8 h average (MDA8) surface ozone over China (0.62 ppbv), NCP (4.56 ppbv), and YRD (5.25 ppbv), suggesting that emission control strategies on VOCs should be prioritized to curb ozone production rates in these regions. Taiwan, Malaysia, and PRD stand out as regions undergoing lower MDA8 ozone levels resulting from the NO_x reductions occurring predominantly in NO_x-sensitive regimes.

ID: 157460
Type: article
Authors: Souri, Amir H.; Nowlan, Caroline R.; Wolfe, Glenn M.; Lamsal, Lok N.; Chan Miller, Christopher E.; González Abad, Gonzalo; Janz, Scott J.; Fried, Alan; Blake, Donald R.; Weinheimer, Andrew J.; Diskin, Glenn S.; Liu, Xiong; Chance, Kelly
Abstract: The authors regret both Fig. S2 and Fig. S3 were inadvertently used a wrong day (06/10 instead of 06/09 due to a difference in the UTC vs local times) for plotting the NASA's LaRC box model output. The new figure shows that both F0AM and LaRC models are in a strong degree of agreement (<10%) suggesting that the non-linear ozone chemistry over Seoul can be reasonably represented by both models. This correction does not impact the conclusion drawn from this study. We thank James H. Crawford for pointing us at the bug.

ID: 157311
Type: article
Authors: Souri, Amir H.; Wang, Huiqun; González Abad, Gonzalo; Liu, Xiong; Chance, Kelly
Abstract: The primary focus of this study is to understand the contribution from excess moisture from crop transpiration to the severity of a heat wave episode that hit the Midwestern U.S. from 16 to 20 July 2011. To elucidate this, we first provide an optimal estimate of the transpiration water vapor flux using satellite total column water vapor retrievals whose accuracy and precision are characterized using independent observations. The posterior transpiration flux is estimated using a local ensemble transform Kalman filter that employs a mesoscale weather model as the forward model. The new estimation suggests that the prior values of transpiration flux from crops are biased high by 15%. We further use the constrained flux to examine the sensitivity of meteorology to the contributions from crops. Over the agricultural areas during daytime, elevated moisture (up to 40%) from crops not only increases humidity (thus the heat index) but also provides a positive radiative forcing by increasing downward longwave radiation (13 ± 4 W m^-2) that results in even higher surface air temperature (+0.4 °C). Consequently, we find that the elevated moisture generally provides positive feedback to aggravate the heat wave, with daytime enhancements of heat index by as large as 3.3 ± 0.8 °C. Due to a strong diurnal cycle in the transpiration, the feedback tends to be stronger in the afternoon (up to 5 °C) and weaker at night. Results offer a potential basis for designing mitigation strategies for the effect of transpiration from agriculture in the future, in addition to improving the estimation of canopy transpiration.

ID: 156335
Type: article
Authors: Souri, Amir Hossein; Nowlan, Caroline R.; Wolfe, Glenn M.; Lamsal, Lok N.; Chan Miller, Christopher E.; Abad, Gonzalo González; Janz, Scott J.; Fried, Alan; Blake, Donald R.; Weinheimer, Andrew J.; Diskin, Glenn S.; Liu, Xiong; Chance, Kelly
Abstract: The nonlinear chemical processes involved in ozone production (P(O₃)) have necessitated using proxy indicators to convey information about the primary dependence of P(O₃) on volatile organic compounds (VOCs) or nitrogen oxides (NO_x). In particular, the ratio of remotely sensed columns of formaldehyde (HCHO) to nitrogen dioxide (NO₂) has been widely used for studying O₃ sensitivity. Previous studies found that the errors in retrievals and the incoherent relationship between the column and the near-surface concentrations are a barrier in applying the ratio in a robust way. In addition to these obstacles, we provide calculational- observational evidence, using an ensemble of 0-D photochemical box models constrained by DC-8 aircraft measurements on an ozone event during the Korea-United States Air Quality (KORUS-AQ) campaign over Seoul, to demonstrate the chemical feedback of NO₂ on the formation of HCHO is a controlling factor for the transition line between NO_x-sensitive and NO_x-saturated regimes. A fixed value (~2.7) of the ratio of the chemical loss of NO_x (LNO_x) to the chemical loss of HO₂+RO₂ (LRO_x) perceptibly differentiates the regimes. Following this value, data points with a ratio of HCHO/NO₂ less than 1 can be safely classified as NO_x-saturated regime, whereas points with ratios between 1 and 4 fall into one or the other regime. We attribute this mainly to the HCHO-NO₂ chemical relationship causing the transition line to occur at larger (smaller) HCHO/NO₂ ratios in VOC-rich (VOC-poor) environments. We then redefine the transition line to LNO_x/LRO_x~2.7 that accounts for the HCHO-NO₂ chemical relationship leading to HCHO = 3.7 × (NO₂ - 1.14 × 10¹⁶ molec.cm^-2). Although the revised formula is locally calibrated (i.e., requires for readjustment for other regions), its mathematical format removes the need for having a wide range of thresholds used in HCHO/NO₂ ratios that is a result of the chemical feedback. Therefore, to be able to properly take the chemical feedback into consideration, the use of HCHO = a × (NO₂ - b) formula should be preferred to the ratio in future works. We then use the Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument to study O₃ sensitivity in Seoul. The unprecedented spatial (250 × 250 m²) and temporal (~every 2 h) resolutions of HCHO and NO₂ observations form the sensor enhance our understanding of P(O₃) in Seoul; rather than providing a crude label for the entire city, more in-depth variabilities in chemical regimes are observed that should be able to inform mitigation strategies correspondingly.

ID: 156855
Type: article
Authors: Vaquero-Martínez, Javier; Antón, Manuel; Román, Roberto; Cachorro, Victoria E.; Wang, Huiqun; González Abad, Gonzalo; Ritter, Christoph

ID: 157528
Type: article
Authors: Zhu, Lei; Abad, Gonzalo Gonzalez; 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 M.; Wolfe, Glenn M.
Abstract: Formaldehyde (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.

ID: 154602
Type: article
Authors: Gonzalez Abad, Gonzalo; Souri, Amir Hossein; Bak, Juseon; Chance, Kelly; Flynn, Lawrence E.; Krotkov, Nickolay A.; Lamsal, Lok; Li, Can; Liu, Xiong; Chan Miller, Christopher; Nowlan, Caroline R.; Suleiman, Raid; Wang, Huiqun
Abstract: Over the last five decades, Earth's atmosphere has been extensively monitored from space using different spectral ranges. Early efforts were directed at improving weather forecasts with the first meteorological satellites launched in the 1960s. Soon thereafter, the intersection between weather, climate and atmospheric chemistry led to the observation of atmospheric composition from space. During the 1970s the Nimbus satellite program started regular monitoring of ozone integrated columns and water vapor profiles using the Backscatter Ultraviolet Spectrometer, the Infrared Interferometer Spectrometer and the Satellite Infrared Spectrometer instruments. Five decades after these pioneer efforts, continuous progress in instrument design, and retrieval techniques allow researchers to monitor tropospheric concentrations of a wide range of species with implications for air quality, climate and weather. The time line of historic, present and future space-borne instruments measuring ultraviolet and visible backscattered solar radiation designed to quantify atmospheric trace gases is presented. We describe the instruments technological evolution and the basic concepts of retrieval theory. We include a review of algorithms developed for ozone, nitrogen dioxide, sulfur dioxide, formaldehyde, bromine monoxide, water vapor and glyoxal, a selection of studies using these algorithms, the challenges they face and how these challenges can be addressed. The paper ends by providing insights on the opportunities that new instruments will bring to the atmospheric chemistry, weather and air quality communities and how to address the pressing need for long-term, inter-calibrated data records necessary to monitor the response of the atmosphere to rapidly changing ecosystems.

ID: 155115
Type: article
Authors: Jung, Yeonjin; González Abad, Gonzalo; Nowlan, Caroline R.; Chance, Kelly; Liu, Xiong; Torres, Omar; Ahn, Changwoo
Abstract: Atmospheric aerosols are significant sources of uncertainty in air mass factor (AMF) calculations for trace gas retrievals using ultraviolet measurements from space. Current trace gas retrievals typically do not consider aerosols explicitly as cloud products partially account for aerosol effects. Here, we propose a new measurement-based approach to correct for aerosols explicitly in the AMF calculation, apply it to Ozone Monitoring Instrument (OMI) formaldehyde (HCHO) retrievals and quantify the aerosol-induced HCHO vertical column density difference for three aerosol types (smoke, dust, and sulfate) during 2006-2007. We use OMI aerosol retrievals for aerosol optical properties and vertical profiles to construct lookup tables of scattering weights as functions of geometry, surface pressure, surface albedo, and aerosol information. The average difference between the National Aeronautics and Space Administration operational OMI HCHO product (not considering aerosols) and the results obtained in this study on a global scale are 27%, 6%, and -0.3% for smoke, dust, and sulfate aerosols, respectively. The region with the largest aerosol effects is East China, where the explicit smoke aerosol correction enhances mean HCHO vertical column densities by 35%, with corrections to individual observations sometimes larger than 100%. The quantified aerosol effects are applicable under clear-sky conditions. This study highlights the need to implement aerosol corrections in the AMF calculation for HCHO retrievals. This is particularly relevant in regions with high levels of pollution where aerosols interfere the most with formaldehyde satellite observations.

ID: 154160
Type: article
Authors: Kwon, Hyeong-Ahn; Park, Rokjin J.; González Abad, Gonzalo; Chance, Kelly; Kurosu, Thomas P.; Kim, Jhoon; De Smedt, Isabelle; Van Roozendael, Michel; Peters, Enno; Burrows, John
Abstract: We describe a formaldehyde (HCHO) retrieval algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS) that will be launched by the Korean Ministry of Environment in 2019. The algorithm comprises three steps: preprocesses, radiance fitting, and postprocesses. The preprocesses include a wavelength calibration, as well as interpolation and convolution of absorption cross sections radiance fitting is conducted using a nonlinear fitting method referred to as basic optical absorption spectroscopy (BOAS); and postprocesses include air mass factor calculations and bias corrections. In this study, several sensitivity tests are conducted to examine the retrieval uncertainties using the GEMS HCHO algorithm. We evaluate the algorithm with the Ozone Monitoring Instrument (OMI) Level 1B irradiance/radiance data by comparing our retrieved HCHO column densities with OMI HCHO products of the Smithsonian Astrophysical Observatory (OMHCHO) and of the Quality Assurance for Essential Climate Variables project (OMI QA4ECV). Results show that OMI HCHO slant columns retrieved using the GEMS algorithm are in good agreement with OMHCHO, with correlation coefficients of 0.77-0.91 and regression slopes of 0.94-1.04 for March, June, September, and December 2005. Spatial distributions of HCHO slant columns from the GEMS algorithm are consistent with the OMI QA4ECV products, but relatively poorer correlation coefficients of 0.52-0.76 are found compared to those against the OMHCHO products. Also, we compare the satellite results with ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations. OMI GEMS HCHO vertical columns are 9 %-25 % lower than those of MAX-DOAS at Haute- Provence Observatory (OHP) in France, Bremen in Germany, and Xianghe in China. We find that the OMI GEMS retrievals have less bias than the OMHCHO and OMI QA4ECV products at OHP and Bremen in comparison with MAX- DOAS.

ID: 155325
Type: article
Authors: Liao, Jin; Hanisco, Thomas F.; Wolfe, Glenn M.; St. Clair, Jason; Jimenez, Jose L.; Campuzano-Jost, Pedro; Nault, Benjamin A.; Fried, Alan; Marais, Eloise A.; Gonzalez Abad, Gonzalo; Chance, Kelly; Jethva, Hiren T.; Ryerson, Thomas B.; Warneke, Carsten; Wisthaler, Armin
Abstract: Organic aerosol (OA) is one of the main components of the global particulate burden and intimately links natural and anthropogenic emissions with air quality and climate. It is challenging to accurately represent OA in global models. Direct quantification of global OA abundance is not possible with current remote sensing technology; however, it may be possible to exploit correlations of OA with remotely observable quantities to infer OA spatiotemporal distributions. In particular, formaldehyde (HCHO) and OA share common sources via both primary emissions and secondary production from oxidation of volatile organic compounds (VOCs). Here, we examine OA-HCHO correlations using data from summertime airborne campaigns investigating biogenic (NASA SEAC⁴RS and DC3), biomass burning (NASA SEAC⁴RS), and anthropogenic conditions (NOAA CalNex and NASA KORUS-AQ). In situ OA correlates well with HCHO (r=0.59-0.97), and the slope and intercept of this relationship depend on the chemical regime. For biogenic and anthropogenic regions, the OA-HCHO slopes are higher in low NO_x conditions, because HCHO yields are lower and aerosol yields are likely higher. The OA-HCHO slope of wildfires is over 9 times higher than that for biogenic and anthropogenic sources. The OA-HCHO slope is higher for highly polluted anthropogenic sources (e.g., KORUS- AQ) than less polluted (e.g., CalNex) anthropogenic sources. Near- surface OAs over the continental US are estimated by combining the observed in situ relationships with HCHO column retrievals from NASA's Ozone Monitoring Instrument (OMI). HCHO vertical profiles used in OA estimates are from climatology a priori profiles in the OMI HCHO retrieval or output of specific period from a newer version of GEOS- Chem. Our OA estimates compare well with US EPA IMPROVE data obtained over summer months (e.g., slope =0.60-0.62, r=0.56 for August 2013), with correlation performance comparable to intensively validated GEOS- Chem (e.g., slope =0.57, r=0.56) with IMPROVE OA and superior to the satellite-derived total aerosol extinction (r=0.41) with IMPROVE OA. This indicates that OA estimates are not very sensitive to these HCHO vertical profiles and that a priori profiles from OMI HCHO retrieval have a similar performance to that of the newer model version in estimating OA. Improving the detection limit of satellite HCHO and expanding in situ airborne HCHO and OA coverage in future missions will improve the quality and spatiotemporal coverage of our OA estimates, potentially enabling constraints on global OA distribution.

ID: 155131
Type: article
Authors: López-Morales, Mercedes; Ben-Ami, Sagi; Gonzalez-Abad, Gonzalo; García-Mejía, Juliana; Dietrich, Jeremy; Szentgyorgyi, Andrew
Abstract: We present the result of calculations to optimize the search for molecular oxygen, O₂, in Earth analogs transiting around nearby, low-mass stars using ground-based, high-resolution Doppler shift techniques. We investigate a series of parameters, namely spectral resolution, wavelength coverage of the observations, and sky coordinates and systemic velocity of the exoplanetary systems, to find the values that optimize detectability of O₂. We find that increasing the spectral resolution of observations to R ∼ 300,000-400,000 from the typical R ∼ 100,000 more than doubles the average depth of O₂ lines in planets with atmospheres similar to Earth's. Resolutions higher than ∼500,000 do not produce significant gains in the depths of the O₂ lines. We confirm that observations in the O₂ A-band are the most efficient except for M9V host stars, for which observations in the O₂ near-infrared (NIR) band are more efficient. Combining observations in the O₂ A, B, and NIR bands can reduce the number of transits needed to produce a detection of O₂ by about one-third in the case of white noise limited observations. However, that advantage disappears in the presence of typical levels of red noise. Therefore, combining observations in more than one band produces no significant gain versus observing only in the A band, unless red noise can be significantly reduced. Blending between the exoplanet's O₂ lines and telluric O₂ lines is a known problem. We find that problem can be alleviated by increasing the resolution of the observations, and by giving preference to targets near the ecliptic.

ID: 155159
Type: article
Authors: Shen, Lu; Jacob, Daniel J.; Zhu, Lei; Zhang, Qiang; Zheng, Bo; Sulprizio, Melissa P.; Li, Ke; De Smedt, Isabelle; González Abad, Gonzalo; Cao, Hansen; Fu, Tzung-May; Liao, Hong
Abstract: We use 2005-2016 observations of formaldehyde (HCHO) columns over China from the OMI, GOME-2, and SCIAMACHY satellite instruments to evaluate long-term trends in emission inventories of volatile organic compounds (VOCs) that affect air quality. The observations show large increases over 2005-2016 in the North China Plain (+1.1 ± 0.5% a^-1 relative to 2005) and the Yangtze River Delta region (+1.5 ± 0.4% a^-1 relative to 2005), consistent with the trend of anthropogenic VOC emissions in the Multi-resolution Emission Inventory for China (MEIC). Unlike other pollutants, VOC emissions have not been decreasing in recent years. An exception is the Huai River Basin in rural eastern China where the satellite data show rapidly decreasing VOC emissions since the early 2010s that appear to reflect bans on agricultural fires.

ID: 155235
Type: article
Authors: Suleiman, Raid M.; Chance, Kelly; Liu, Xiong; González Abad, Gonzalo; Kurosu, Thomas P.; Hendrick, Francois; Theys, Nicolas
Abstract: This paper presents the retrieval algorithm for the operational Ozone Monitoring Instrument (OMI) total bromine monoxide (BrO) data product (OMBRO) developed at the Smithsonian Astrophysical Observatory (SAO) and shows comparisons with correlative measurements and retrieval results. The algorithm is based on direct nonlinear least squares fitting of radiances from the spectral range 319.0-347.5 nm. Radiances are modeled from the solar irradiance, attenuated by contributions from BrO and interfering gases, and including rotational Raman scattering, additive and multiplicative closure polynomials, correction for Nyquist undersampling and the average fitting residual spectrum. The retrieval uses albedo- and wavelength-dependent air mass factors (AMFs), which have been pre-computed using a single mostly stratospheric BrO profile. The BrO cross sections are multiplied by the wavelength-dependent AMFs before fitting so that the vertical column densities (VCDs) are retrieved directly. The fitting uncertainties of BrO VCDs typically vary between 4 and 7×10¹² molecules cm^-2 (̃10 %-20 % of the measured BrO VCDs). Additional fitting uncertainties can be caused by the interferences from O₂-O₂ and H₂CO and their correlation with BrO. AMF uncertainties are estimated to be around 10 % when the single stratospheric-only BrO profile is used. However, under conditions of high tropospheric concentrations, AMF errors due to this assumption of profile can be as high as 50 %. The retrievals agree well with GOME-2 observations at simultaneous nadir overpasses and with ground-based zenith-sky measurements at Harestua, Norway, with mean biases less than -0.22±1.13×¹⁰¹³ and 0.12±0.76×¹⁰¹³ molecules cm^-2, respectively. Global distribution and seasonal variation of OMI BrO are generally consistent with previous satellite observations. Finally, we confirm the capacity of OMBRO retrievals to observe enhancements of BrO over the US Great Salt Lake despite the current retrieval setup considering a stratospheric profile in the AMF calculations. OMBRO retrievals also show significant BrO enhancements from the eruption of the Eyjafjallajökull volcano, although the BrO retrievals are affected under high SO₂ loading conditions by the sub-optimum choice of SO₂ cross sections.

ID: 152896
Type: article
Authors: Wolfe, Glenn M.; Nicely, Julie M.; St. Clair, Jason M.; Hanisco, Thomas F.; Liao, Jin; Oman, Luke D.; Brune, William B.; Miller, David; Thames, Alexander; González Abad, Gonzalo; Ryerson, Thomas B.; Thompson, Chelsea R.; Peischl, Jeff; McCain, Kathryn; Sweeney, Colm; Wennberg, Paul O.; Kim, Michelle; Crounse, John D.; Hall, Samuel R.; Ullmann, Kirk; Diskin, Glenn; Bui, Paul; Chang, Cecilia; Dean-Day, Jonathan
Abstract: The hydroxyl radical (OH) fuels tropospheric ozone production and governs the lifetime of methane and many other gases. Existing methods to quantify global OH are limited to annual and global-to-hemispheric averages. Finer resolution is essential for isolating model deficiencies and building process-level understanding. In situ observations from the Atmospheric Tomography (ATom) mission demonstrate that remote tropospheric OH is tightly coupled to the production and loss of formaldehyde (HCHO), a major hydrocarbon oxidation product. Synthesis of this relationship with satellite-based HCHO retrievals and model-derived HCHO loss frequencies yields a map of total-column OH abundance throughout the remote troposphere (up to 70% of tropospheric mass) over the first two ATom missions (August 2016 and February 2017). This dataset offers unique insights on near-global oxidizing capacity. OH exhibits significant seasonality within individual hemispheres, but the domain mean concentration is nearly identical for both seasons (1.03 ± 0.25 × 106 cm‑3), and the biseasonal average North/South Hemisphere ratio is 0.89 ± 0.06, consistent with a balance of OH sources and sinks across the remote troposphere. Regional phenomena are also highlighted, such as a 10-fold OH depression in the Tropical West Pacific and enhancements in the East Pacific and South Atlantic. This method is complementary to budget-based global OH constraints and can help elucidate the spatial and temporal variability of OH production and methane loss.

ID: 147913
Type: article
Authors: Ben-Ami, Sagi; López-Morales, Mercedes; Garcia-Mejia, Juliana; Gonzalez Abad, Gonzalo; Szentgyorgyi, Andrew
Abstract: We present a novel implementation for extremely high-resolution spectroscopy using custom-designed Fabry--Perot Interferometer (FPI) arrays. For a given telescope aperture at the seeing-limited case, these arrays can achieve resolutions well in excess of R ~ 10⁵ using optical elements that are orders of magnitude smaller in size than standard echelle spectrographs of similar resolution. We apply this method specifically to the search for O₂ in exoplanetary atmospheres using the O₂ A band at 0.76 mum and show how an FPI array composed of ~10 etalons with parameters optimized for this science case can record R = 3--5 × 10⁵ spectra covering the full O₂ A band. Using simulated observations of the atmosphere of a transiting nearby Earth-like planet, we show how observations with an FPI array coupled to a long-slit spectrograph can reduce the number of transit observations needed to produce a 3sigma detection of O₂ by ~30% compared to observations with an R = 10⁵ echelle spectrograph. This in turn leads to a decrease in an observing program duration of several years. The number of transits needed for a 3sigma detection can be further reduced by increasing the efficiency of FPI arrays using dualons (an etalon with a buried reflective layer) and by coupling the FPI array to a dedicated spectrograph optimized for the O₂ A band.

ID: 143296
Type: article
Authors: Barkley, Michael P.; González Abad, Gonzalo; Kurosu, Thomas P.; Spurr, Robert; Torbatian, Sara; Lerot, Christophe
Abstract: Using Ozone Monitoring Instrument (OMI) trace gas vertical column observations of nitrogen dioxide (NO₂), formaldehyde (HCHO), sulfur dioxide (SO₂), and glyoxal (CHOCHO), we have conducted a robust and detailed time series analysis to assess changes in local air quality for over 1000 locations (focussing on urban, oil refinery, oil port, and power plant targets) over the Middle East for 2005-2014. Apart from NO₂, which is highest over urban locations, average tropospheric column levels of these trace gases are highest over oil ports and refineries. The highest average pollution levels over urban settlements are typically in Bahrain, Kuwait, Qatar, and the United Arab Emirates.

We detect 278 statistically significant and real linear NO₂ trends in total. Over urban areas NO₂ increased by up to 12 % yr^-1, with only two locations showing a decreasing trend. Over oil refineries, oil ports, and power plants, NO₂ increased by about 2-9 % yr^-1. For HCHO, 70 significant and real trends were detected, with HCHO increasing by 2-7 % yr^-1 over urban settlements and power plants and by about 2-4 % yr^-1 over refineries and oil ports. Very few SO₂ trends were detected, which varied in direction and magnitude (23 increasing and 9 decreasing). Apart from two locations where CHOCHO is decreasing, we find that glyoxal tropospheric column levels are not changing over the Middle East. Hence, for many locations in the Middle East, OMI observes a degradation in air quality over 2005-2014. This study therefore demonstrates the capability of OMI to generate long-term air-quality monitoring at local scales over this region.

ID: 143830
Type: article
Authors: Chan Miller, Christopher; Jacob, Daniel J.; Marais, Eloise A.; Yu, Karen; Travis, Katherine R.; Kim, Patrick S.; Fisher, Jenny A.; Zhu, Lei; Wolfe, Glenn M.; Hanisco, Thomas F.; Keutsch, Frank N.; Kaiser, Jennifer; Min, Kyung-Eun; Brown, Steven S.; Washenfelder, Rebecca A.; González Abad, Gonzalo; Chance, Kelly
Abstract: Glyoxal (CHOCHO) is produced in the atmosphere by the oxidation of volatile organic compounds (VOCs). Like formaldehyde (HCHO), another VOC oxidation product, it is measurable from space by solar backscatter. Isoprene emitted by vegetation is the dominant source of CHOCHO and HCHO in most of the world. We use aircraft observations of CHOCHO and HCHO from the SENEX campaign over the southeast US in summer 2013 to better understand the CHOCHO time-dependent yield from isoprene oxidation, its dependence on nitrogen oxides (NO_x ≡ NO + NO₂), the behavior of the CHOCHO-HCHO relationship, the quality of OMI CHOCHO satellite observations, and the implications for using CHOCHO observations from space as constraints on isoprene emissions. We simulate the SENEX and OMI observations with the Goddard Earth Observing System chemical transport model (GEOS-Chem) featuring a new chemical mechanism for CHOCHO formation from isoprene. The mechanism includes prompt CHOCHO formation under low-NO_x conditions following the isomerization of the isoprene peroxy radical (ISOPO₂). The SENEX observations provide support for this prompt CHOCHO formation pathway, and are generally consistent with the GEOS-Chem mechanism. Boundary layer CHOCHO and HCHO are strongly correlated in the observations and the model, with some departure under low-NO_x conditions due to prompt CHOCHO formation. SENEX vertical profiles indicate a free-tropospheric CHOCHO background that is absent from the model. The OMI CHOCHO data provide some support for this free-tropospheric background and show southeast US enhancements consistent with the isoprene source but a factor of 2 too low. Part of this OMI bias is due to excessive surface reflectivities assumed in the retrieval. The OMI CHOCHO and HCHO seasonal data over the southeast US are tightly correlated and provide redundant proxies of isoprene emissions. Higher temporal resolution in future geostationary satellite observations may enable detection of the prompt CHOCHO production under low-NO_x conditions apparent in the SENEX data.