Publication Search Results

ID: 158981
Type: article
Authors: Wales, Pamela A.; Salawitch, Ross J.; Lind, Elena S.; Mount, George H.; Canty, Timothy P.; Chance, Kelly; Choi, Sungyeon; Donohoue, Deanna; Kurosu, Thomas P.; Simpson, William R.; Suleiman, Raid M.
Abstract: In spring 2011, columns of bromine monoxide (BrO) were retrieved over Fairbanks, Alaska using a ground-based multifunction differential optical absorption spectroscopy (MFDOAS) instrument. MFDOAS vertical column BrO is consistently lower than retrievals from the satellite-based Ozone Monitoring Instrument (OMI), with a relative bias of 20 ± 14%. Numerous tropical-based studies suggest that 5 ± 2 parts per trillion (ppt) of bromine from very short-lived substances (VSLS) reaches the stratosphere. We evaluate upper limits on the contribution of VSLS to stratospheric bromine by treating the column retrievals of BrO as purely stratospheric and modeling the ratio of BrO to total inorganic bromine. The OMI and MFDOAS retrievals respectively present 8 and 5 ppt upper limits on the stratospheric injection of VSLS, and kinetic uncertainties in the daytime partitioning of bromine species decrease both values by ∼1.7 ppt. The OMI-based estimate is in agreement with the 5 ppt tropical-based value for stratospheric injection of VSLS if the tropospheric column of BrO is 1.5 × 10¹³ molecules cm^-2 over Fairbanks, which is within the range of uncertainty of a second ground-based instrument that monitored tropospheric BrO during the campaign. Because our ground-based instruments detected no BrO near the surface, this value for tropospheric BrO would originate from higher altitudes in the troposphere and is in agreement with previous retrievals of background tropospheric BrO. Our calculations of tropospheric BrO over Fairbanks are most sensitive to uncertainties in the stratospheric loading of VSLS, followed by the difference between the OMI and MFDOAS retrievals of BrO.

ID: 157568
Type: article
Authors: Bak, Juseon; Liu, Xiong; Birk, Manfred; Wagner, Georg; Gordon, Iouli E.; Chance, Kelly
Abstract: We evaluate different sets of high-resolution ozone absorption cross-section data for use in atmospheric ozone profile measurements in the Hartley and Huggins bands with a particular focus on BDM 1995 (Daumont et al. 1992; Brion et al., 1993; Malicet et al., 1995), currently used in our retrievals, and a new laboratory dataset by Birk and Wagner (2018) (BW). The BDM cross-section data have been recommended to use for retrieval of ozone profiles using spaceborne nadir-viewing backscattered ultraviolet (BUV) measurements since its improved performance was demonstrated against other cross-sections including Bass and Paur (1985) (BP) and those of Serdyuchenko et al. (2014) and Gorshelev et al. (2014) (SER) by the "Absorption Cross-Sections of Ozone" (ACSO) activity. The BW laboratory data were recently measured within the framework of the European Space Agency (ESA) project SEOM-IAS (Scientific Exploitation of Operational Missions - Improved Atmospheric Spectroscopy Databases) to provide an advanced absorption cross-section database. The BW cross-sections are made from measurements at more temperatures and in a wider temperature range than BDM, especially for low temperatures. Relative differences of cross-sections between BW and BDM range from similar to 2% at shorter UV wavelengths to similar to 5% at longer UV wavelengths at warm temperatures. Furthermore, these differences dynamically increase by up to +/- 40% at cold temperatures due to no BDM measurements having been made below 218 K. We evaluate the impact of using different cross-sections on ozone profile retrievals from Ozone Monitoring Instrument (OMI) measurements. Correspondingly, this impact leads to significant differences in individual ozone retrievals by up to 50% in the tropopause where the coldest atmospheric temperatures are observed. Bottom atmospheric layers illustrate the significant change of the retrieved ozone values, with differences of 20% in low latitudes, which is not the case in high latitudes because the ozone retrievals are mainly controlled by a priori ozone information in high latitudes due to less photon penetration down to the lower troposphere. Validation with ozonesonde observations demonstrates that BW and BDM retrievals show altitude-dependent bias oscillations of similar magnitude relative to ozonesonde measurements, much smaller than those of both BP and SER retrievals. However, compared to BDM, BW retrievals show significant reduction in standard deviation, by up to 15 %, especially at the coldest atmospheric temperatures. Such improvement is achieved mainly by the better characterization of the temperature dependence of ozone absorption.

ID: 158010
Type: article
Authors: Conway, Eamon K.; Gordon, Iouli E.; Tennyson, Jonathan; Polyansky, Oleg L.; Yurchenko, Sergei N.; Chance, Kelly
Abstract: Accurate reference spectroscopic information for the water molecule from the microwave to the near-ultraviolet is of paramount importance in atmospheric research. A semi-empirical potential energy surface for the ground electronic state of H₂¹⁶O has been created by refining almost 4000 experimentally determined energy levels. These states extend into regions with large values of rotational and vibrational excitation. For all states considered in our refinement procedure, which extend to 37 000 cm^-1 and J=20 (total angular momentum), the average root-mean-square deviation is approximately 0.05 cm^-1. This potential energy surface offers significant improvements when compared to recent models by accurately predicting states possessing high values of J. This feature will offer significant improvements in calculated line positions for high-temperature spectra where transitions between high J states become more prominent.
Combining this potential with the latest dipole moment surface for water vapour, a line list has been calculated which extends reliably to 37 000 cm^-1. Obtaining reliable results in the ultraviolet is of special importance as it is a challenging spectral region for the water molecule both experimentally and theoretically. Comparisons are made against several experimental sources of cross sections in the near-ultraviolet and discrepancies are observed. In the near-ultraviolet our calculations are in agreement with recent atmospheric retrievals and the upper limit obtained using broadband spectroscopy by Wilson et al. (2016, p. 194), but they do not support recent suggestions of very strong absorption in this region.

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: 157461
Type: article
Authors: Souri, Amir H.; Choi, Yunsoo; Kodros, John K.; Jung, Jia; Shpund, Jacob; Pierce, Jeffrey R.; Lynn, Barry H.; Khain, Alexander; Chance, Kelly
Abstract: A number of human-induced elements contribute to influencing the intensity of tropical cyclones and prolonging their lifetime. Not only do ocean heat content, large-scale weather patterns, and surface properties affect the amount of release of energy, but the modulation from aerosol particles on cloud properties is also present. With Hurricane Harvey (2017) fairly isolated over Texas, there was a unique opportunity to study the indirect impact of aerosols on the amount of record-breaking rainfall over the greater Houston area. Due to the non-linear processes involved in clouds microstructure, aerosol properties and the variability associated with the atmospheric environment, the quantification of the response of storms to aerosols is complex. To this end, we first reproduce Harvey using the Weather Research and Forecasting (WRF) model coupled with a 3D-var assimilation framework that incorporates satellites, radio occultation, dropsondes, and surface measurements. We then study the aerosol indirect impacts using spectral bin microphysics in conjunction with aerosol properties simulated from the Goddard Earth Observing System (GEOS)-Chem TwO-Moment Aerosol Sectional (TOMAS) model leveraging online aerosol microphysics with anthropogenic emissions (SP) and without ones (SC). In the vicinity of Harvey's landfall, the number concentration of cloud condensation nuclei at 1% supersaturation using the anthropogenic emissions is found to be one order of magnitude (855 cm^-3) larger than those simulated with only natural emissions (83 cm^-3). We observed that a narrow plume of anthropogenic aerosols from western Texas was transported over the area at the moment when deep convection initiated, accelerating updrafts through releasing more latent heat, which in turn, resulted in an average enhancement of precipitation by 25 mm (~ 8%) over the greater Houston area. We observed a second peak at the right tail of the distribution of differences between experiments, which is an indication of the presence of more extreme rainfall over the area. As such, studies on the impact of aerosol emissions controls on exacerbating severe weather should be more encouraged.

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: 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: 154401
Type: article
Authors: Bak, Juseon; Baek, Kang-Hyeon; Kim, Jae-Hwan; Liu, Xiong; Kim, Jhoon; Chance, Kelly
Abstract: The Geostationary Environment Monitoring Spectrometer (GEMS) is scheduled to be launched in 2019-2020 on board the GEO-KOMPSAT (GEOstationary KOrea Multi-Purpose SATellite)-2B, contributing as the Asian partner of the global geostationary constellation of air quality monitoring. To support this air quality satellite mission, we perform a cross-evaluation of simulated GEMS ozone profile retrievals from OMI (Ozone Monitoring Instrument) data based on the optimal estimation and ozonesonde measurements within the GEMS domain, covering from 5^∘ S (Indonesia) to 45^∘ N (south of the Russian border) and from 75 to 145^∘ E. The comparison between ozonesonde and GEMS shows a significant dependence on ozonesonde types. Ozonesonde data measured by modified Brewer-Mast (MBM) at Trivandrum and New Delhi show inconsistent seasonal variabilities in tropospheric ozone compared to carbon-iodine (CI) and electrochemical condensation cell (ECC) ozonesondes at other stations in a similar latitude regime. CI ozonesonde measurements are negatively biased relative to ECC measurements by 2-4 DU; better agreement is achieved when simulated GEMS ozone retrievals are compared to ECC measurements. ECC ozone data at Hanoi, Kuala Lumpur, and Singapore show abnormally worse agreements with simulated GEMS retrievals than other ECC measurements. Therefore, ECC ozonesonde measurements at Hong Kong, Pohang, Naha, Sapporo, and Tsukuba are finally identified as an optimal reference dataset. The accuracy of simulated GEMS retrievals is estimated to be ̃5.0 % for both tropospheric and stratospheric column ozone with the precision of 15 %and 5 %, which meets the GEMS ozone requirements.

ID: 154165
Type: article
Authors: Bak, Juseon; Liu, Xiong; Sun, Kang; Chance, Kelly; Kim, Jae-Hwan
Abstract: We introduce a method that accounts for errors caused by the slit function in an optimal-estimation-based spectral fitting process to improve ozone profile retrievals from the Ozone Monitoring Instrument (OMI) ultraviolet measurements (270-330 nm). Previously, a slit function was parameterized as a standard Gaussian by fitting the full width at half maximum (FWHM) of the slit function from climatological OMI solar irradiances. This cannot account for the temporal variation in slit function in irradiance, the intra-orbit changes due to thermally induced change and scene inhomogeneity, and potential differences in the slit functions of irradiance and radiance measurements. As a result, radiance simulation errors may be induced due to convolving reference spectra with incorrect slit functions. To better represent the shape of the slit functions, we implement a more generic super Gaussian slit function with two free parameters (slit width and shape factor); it becomes standard Gaussian when the shape factor is fixed to be 2. The effects of errors in slit function parameters on radiance spectra, referred to as pseudo absorbers (PAs), are linearized by convolving high-resolution cross sections or simulated radiances with the partial derivatives of the slit function with respect to the slit parameters. The PAs are included in the spectral fitting scaled by fitting coefficients that are iteratively adjusted as elements of the state vector along with ozone and other fitting parameters. The fitting coefficients vary with cross-track and along-track pixels and show sensitivity to heterogeneous scenes. The PA spectrum is quite similar in the Hartley band below 310 nm for both standard and super Gaussians, but is more distinctly structured in the Huggins band above 310 nm with the use of super Gaussian slit functions. Finally, we demonstrate that some spikes of fitting residuals are slightly smoothed by accounting for the slit function errors. Comparisons with ozonesondes demonstrate noticeable improvements when using PAs for both standard and super Gaussians, especially for reducing the systematic biases in the tropics and midlatitudes (mean biases of tropospheric column ozone reduced from -1.4̃0.7 to 0.0̃0.4 DU) and reducing the standard deviations of tropospheric ozone column differences at high latitudes (by 1 DU for the super Gaussian). Including PAs also makes the retrievals consistent between standard and super Gaussians. This study corroborates the slit function differences between radiance and irradiance, demonstrating that it is important to account for such differences in the ozone profile retrievals.

ID: 154635
Type: article
Authors: Cusworth, Daniel H.; Jacob, Daniel J.; Varon, Daniel J.; Chan Miller, Christopher; Liu, Xiong; Chance, Kelly; Thorpe, Andrew K.; Duren, Riley M.; Miller, Charles E.; Thompson, David R.; Frankenberg, Christian; Guanter, Luis; Randles, Cynthia A.
Abstract: We examine the potential for global detection of methane plumes from individual point sources with the new generation of spaceborne imaging spectrometers (EnMAP, PRISMA, EMIT, SBG, CHIME) scheduled for launch in 2019-2025. These instruments are designed to map the Earth's surface at high spatial resolution (30 m×30 m) and have a spectral resolution of 7-10 nm in the 2200-2400 nm band that should also allow useful detection of atmospheric methane. We simulate scenes viewed by EnMAP (10 nm spectral resolution, 180 signal-to-noise ratio) using the EnMAP end-to- end simulation tool with superimposed methane plumes generated by large- eddy simulations. We retrieve atmospheric methane and surface reflectivity for these scenes using the IMAP-DOAS optimal estimation algorithm. We find an EnMAP precision of 3 %-7 % for atmospheric methane depending on surface type. This allows effective single-pass detection of methane point sources as small as 100 kg h^-1 depending on surface brightness, surface homogeneity, and wind speed. Successful retrievals over very heterogeneous surfaces such as an urban mosaic require finer spectral resolution. We tested the EnMAP capability with actual plume observations over oil/gas fields in California from the Airborne Visible/Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) sensor (3 m×3 m pixel resolution, 5 nm spectral resolution, SNR 200-400), by spectrally and spatially downsampling the AVIRIS-NG data to match EnMAP instrument specifications. Results confirm that EnMAP can successfully detect point sources of ̃100 kg h^-1 over bright surfaces. Source rates inferred with a generic integrated mass enhancement (IME) algorithm were lower for EnMAP than for AVIRIS- NG. Better agreement may be achieved with a more customized IME algorithm. Our results suggest that imaging spectrometers in space could play an important role in the future for quantifying methane emissions from point sources worldwide.

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: 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: 145771
Type: article
Authors: Huang, Guanyu; Liu, Xiong; Chance, Kelly; Yang, Kai; Cai, Zhaonan
Abstract: We validate the Ozone Monitoring Instrument (OMI) ozone profile (PROFOZ v0.9.3) product including ozone profiles between 0.22 and 261 hPa and stratospheric ozone columns (SOCs) down to 100, 215, and 261 hPa from October 2004 through December 2014 retrieved by the Smithsonian Astrophysical Observatory (SAO) algorithm against the latest Microwave Limb Sound (MLS) v4.2x data. We also evaluate the effects of OMI row anomaly (RA) on the retrieval by dividing the data set into before and after the occurrence of serious RA, i.e., pre-RA (2004-2008) and post-RA (2009-2014). During the pre-RA period, OMI ozone profiles agree very well with MLS data. After applying OMI averaging kernels to MLS data, the global mean biases (MBs) are within 3 % between 0.22 and 100 hPa, negative biases are within 3-9 % for lower layers, and the standard deviations (SDs) are 3.5-5 % from 1 to 40 hPa, 6-10 % for upper layers, and 5-20 % for lower layers. OMI shows biases dependent on latitude and solar zenith angle (SZA), but MBs and SDs are mostly within 10 % except for low and high altitudes of high latitudes and SZAs. Compared to the retrievals during the pre-RA period, OMI retrievals during the post-RA period degrade slightly between 5 and 261 hPa with MBs and SDs typically larger by 2-5 %, and degrade much more for pressure less than &tilde; 5 hPa, with larger MBs by up to 8 % and SDs by up to 15 %, where the MBs are larger by 10-15 % south of 40° N due to the blockage effect of

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.