@article {651650, title = {NOx Emission Reduction and Recovery during COVID-19 in East China}, journal = {Atmosphere}, volume = {11}, year = {2020}, pages = {433}, abstract = {Since its first confirmed case at the end of 2019, COVID-19 has become a global pandemic in three months with more than 1.4 million confirmed cases worldwide, as of early April 2020. Quantifying the changes of pollutant emissions due to COVID-19 and associated governmental control measures is crucial to understand its impacts on economy, air pollution, and society. We used the WRF-GC model and the tropospheric NO2 column observations retrieved by the TROPOMI instrument to derive the top-down NOx emission change estimation between the three periods: P1 (January 1st to January 22nd, 2020), P2 (January 23rd, Wuhan lockdown, to February 9th, 2020), and P3 (February 10th, back-to-work day, to March 12th, 2020). We found that NOx emissions in East China averaged during P2 decreased by 50\% compared to those averaged during P1. The NOx emissions averaged during P3 increased by 26\% compared to those during P2. Most provinces in East China gradually regained some of their NOx emissions after February 10, the official back-to-work day, but NOx emissions in most provinces have not yet to return to their previous levels in early January. NOx emissions in Wuhan, the first epicenter of COVID-19, had no sign of emission recovering by March 12. A few provinces, such as Zhejiang and Shanxi, have recovered fast, with their averaged NOx emissions during P3 almost back to pre-lockdown levels.}, url = {https://www.mdpi.com/2073-4433/11/4/433}, author = {Zhang, Ruixiong and Zhang, Yuzhong and Haipeng Lin and Xu Feng and Tzung-May Fu and Wang, Yuhang} } @article {641858, title = {Quantifying methane emissions from the largest oil-producing basin in the United States from space}, journal = {Science Advances}, volume = {6}, year = {2020}, abstract = {Using new satellite observations and atmospheric inverse modeling, we report methane emissions from the Permian Basin, which is among the world{\textquoteright}s most prolific oil-producing regions and accounts for \>30\% of total U.S. oil production. Based on satellite measurements from May 2018 to March 2019, Permian methane emissions from oil and natural gas production are estimated to be 2.7 {\textpm} 0.5 Tg a-1, representing the largest methane flux ever reported from a U.S. oil/gas-producing region and are more than two times higher than bottom-up inventory-based estimates. This magnitude of emissions is 3.7\% of the gross gas extracted in the Permian, i.e., ~60\% higher than the national average leakage rate. The high methane leakage rate is likely contributed by extensive venting and flaring, resulting from insufficient infrastructure to process and transport natural gas. This work demonstrates a high-resolution satellite data{\textendash}based atmospheric inversion framework, providing a robust top-down analytical tool for quantifying and evaluating subregional methane emissions.}, url = {https://doi.org/10.1126/sciadv.aaz5120}, author = {Zhang, Yuzhong and Ritesh Gautam and Sudhanshu Pandey and Mark Omara and Joannes D. Maasakkers and Pankaj Sadavarte and Lyon, David and Hannah Nesser and Melissa P. Sulprizio and Daniel J. Varon and Zhang, Ruixiong and Sander Houweling and Zavala-Araiza, Daniel and Ramon A. Alvarez and Alba Lorente and Steven P. Hamburg and Aben, Ilse and Daniel J. Jacob} } @article {649964, title = {Ozone Pollution over China and India: Seasonality and Sources}, journal = {Atmospheric Chemistry and Physics}, volume = {20}, number = {7}, year = {2020}, pages = {4399{\textendash}4414}, abstract = {A regional fully coupled meteorology{\textendash}chemistry model, Weather Research and Forecasting model with Chemistry (WRF-Chem), was employed to study the seasonality of ozone (O3) pollution and its sources in both China and India. Observations and model results suggest that\ O3\ in the North China Plain (NCP), Yangtze River Delta (YRD), Pearl River Delta (PRD), and India exhibit distinctive seasonal features, which are linked to the influence of summer monsoons. Through a factor separation approach, we examined the sensitivity of\ O3\ to individual anthropogenic, biogenic, and biomass burning emissions. We found that summer\ O3\ formation in China is more sensitive to industrial and biogenic sources than to other source sectors, while the transportation and biogenic sources are more important in all seasons for India. Tagged simulations suggest that local sources play an important role in the formation of the summer\ O3\ peak in the NCP, but sources from Northwest China should not be neglected to control summer\ O3\ in the NCP. For the YRD region, prevailing winds and cleaner air from the ocean in summer lead to reduced transport from polluted regions, and the major source region in addition to local sources is Southeast China. For the PRD region, the upwind region is replaced by contributions from polluted PRD as autumn approaches, leading to an autumn peak. The major upwind regions in autumn for the PRD are YRD (11 \%) and Southeast China (10 \%). For India, sources in North India are more important than sources in the south. These analyses emphasize the relative importance of source sectors and regions as they change with seasons, providing important implications for\ O3\ control strategies.}, url = {https://doi.org/10.5194/acp-20-4399-2020}, author = {Meng Gao and Jinhui Gao and Bin Zhu and Kumar, Rajesh and Xiao Lu and Shaojie Song and Zhang, Yuzhong and Beixi Jia and Peng Wang and Gufran Beig and Jianlin Hu and Qi Ying and Hongliang Zhang and Peter Sherman and Michael B. McElroy} } @article {649965, title = {Rapid increases in warm-season surface ozone and resulting health impact over China since 2013}, journal = {Environmental Science \& Technology Letters}, volume = {7}, year = {2020}, pages = {240-247}, abstract = {China{\textquoteright}s nationwide ozone monitoring network initiated in 2013 has observed severe surface ozone pollution. This network, combined with the recent Tropospheric Ozone Assessment Report (TOAR) data set, offers a more comprehensive view on global surface ozone distribution and trends. Here, we report quantitative estimates of the warm-season (April{\textendash}September) surface ozone trends and resulting health impacts at Chinese cities in 2013{\textendash}2019. Both the parametric and nonparametric linear trends for 12 ozone metrics relevant to human health and vegetation exposure are derived. We find that all ozone metrics averaged from Chinese urban sites have increased significantly since 2013. The warm-season daily maximum 8-h average (MDA8) ozone levels increased by 2.4 ppb (5.0\%) year{\textendash}1, with over 90\% of the sites showing positive trends and 30\% with trends larger than 3.0 ppb year{\textendash}1. These rates are among the fastest trends, even faster in some Chinese cities, compared with the urban ozone trends in any other region worldwide reported in TOAR. Ozone metrics reflecting the cumulative exposure effect on human health and vegetation such as SOMO35 and AOT40 have increased at even faster rates (\>10\% year{\textendash}1). We estimate that the total premature respiratory mortalities attributable to ambient MDA8 ozone exposure in 69 Chinese cities are 64,370 in 2019, which has increased by 60\% compared to 2013 levels and requires urgent attention.}, url = {https://doi.org/10.1021/acs.estlett.0c00171}, author = {Xiao Lu and Zhang, Lin and Xiaolin Wang and Meng Gao and Ke Li and Zhang, Yuzhong and Xu Yue and Yuanhang Zhang} } @article {639061, title = {Modeling the global radiative effect of brown carbon: a potentially larger heating source in the tropical free troposphere than black carbon}, journal = {Atmos. Chem. Phys. }, volume = {20}, year = {2020}, pages = {1901{\textendash}1920}, abstract = {Carbonaceous aerosols significantly affect global radiative forcing and climate through absorption and the scattering of sunlight. Black carbon (BC) and brown carbon (BrC) are light-absorbing carbonaceous aerosols. The direct radiative effect (DRE) of BrC is uncertain. A recent study suggests that BrC absorption is comparable to BC in the upper troposphere over biomass burning regions and that the resulting radiative heating tends to stabilize the atmosphere. Yet current climate models do not include proper physical and chemical treatments of BrC. In this study, we derived a BrC global biomass burning emission inventory on the basis of the Global Fire Emissions Database version 4 (GFED4), developed a module to simulate the light absorption of BrC in the Community Atmosphere Model version 5 (CAM5) of the Community Earth System Model (CESM), and investigated the photobleaching effect and convective transport of BrC on the basis of Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and Deep Convective Clouds and Chemistry Project (DC3) measurements. The model simulations of BC were also evaluated using HIAPER (HighPerformance Instrumented Airborne Platform for Environmental Research) Pole-to-Pole Observations (HIPPO) measurements. We found that globally BrC is a significant absorber, the DRE of which is 0.10 W m-2 , more than 25 \% of BC DRE (+0.39 W m-2 ). Most significantly, model results indicated that BrC atmospheric heating in the tropical mid and upper troposphere is larger than that of BC. The source of\ tropical BrC is mainly from wildfires, which are more prevalent in the tropical regions than higher latitudes and release much more BrC relative to BC than industrial sources. While BC atmospheric heating is skewed towards the northern midlatitude lower atmosphere, BrC heating is more centered in the tropical free troposphere. A possible mechanism for the enhanced convective transport of BrC is that hydrophobic high molecular weight BrC becomes a larger fraction of the BrC and less easily activated in a cloud as the aerosol ages. The contribution of BrC heating to the Hadley circulation and latitudinal expansion of the tropics is likely comparable to BC heating.}, url = {https://doi.org/10.5194/acp-20-1901-2020}, author = {Aoxing Zhang and Wang, Yuhang and Zhang, Yuzhong and Weber, Rodney J. and Yongjia Song and Ziming Ke and Zou, Yufei} } @article {643801, title = {Thermodynamic Modeling Suggests Declines in Water Uptake and Acidity of Inorganic Aerosols in Beijing Winter Haze Events during 2014/2015-2018/2019}, journal = {Environmental Science and Technology Letters}, year = {2019}, abstract = {During recent years, aggressive air pollution mitigation measures in northern China have resulted in considerable changes in gas and aerosol chemical composition. But it is unclear whether aerosol water content and acidity respond to these changes. The two parameters have been shown to affect heterogenous production of winter haze aerosols. Here, we performed thermodynamic equilibrium modeling using chemical and meteorological data observed in urban Beijing for four recent winter seasons and quantified the changes in the mass growth factor and pH of inorganic aerosols. We focused on high relative humidity (\> 60\%) conditions when submicron particles have been shown to be in the liquid state. From 2014/2015 to 2018/2019, the modeled mass growth factor decreased by about 9\%{\textendash}17\% due to changes in aerosol compositions (more nitrate and less sulfate and chloride) and the modeled pH increased by about 0.3{\textendash}0.4 unit mainly due to rising ammonia. A buffer equation is derived from semivolatile ammonia partitioning, which helps understand the sensitivity of pH to meteorological and chemical variables. The findings provide implications for evaluating the potential chemical feedback in secondary aerosol production and the effectiveness of ammonia control as a measure to alleviate winter haze.}, url = {https://doi.org/10.1021/acs.estlett.9b00621}, author = {Shaojie Song and Nenes, Athanasios and Meng Gao and Zhang, Yuzhong and Pengfei Liu and Jingyuan Shao and Dechao Ye and Weiqi Xu and Lu Lei and Yele Sun and Baoxian Liu and Shuxiao Wang and Michael B. McElroy} } @article {630959, title = {Fine particulate matter (PM2.5) trends in China, 2013-2018: separating contributions from anthropogenic emissions and meteorology}, journal = { Atmos. Chem. Phys. }, volume = {19}, year = {2019}, month = {Aug 2019}, pages = {11031{\textendash}11041}, url = {https://www.atmos-chem-phys.net/19/11031/2019/}, author = {Shixian Zhai and Daniel J. Jacob and Xuan Wang and Shen, Lu and Ke Li and Zhang, Yuzhong and Ke Gui and Tianliang Zhao and Hong Liao} } @article {629291, title = {Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010{\textendash}2015}, journal = {Atmospheric Chemistry and Physics}, volume = {19}, number = {11}, year = {2019}, month = {June 2019}, pages = {7859-7881}, abstract = {We use 2010{\textendash}2015 observations of atmospheric methane columns from the GOSAT satellite instrument in a global inverse analysis to improve estimates of methane emissions and their trends over the period, as well as the global concentration of tropospheric OH (the hydroxyl radical, methane{\textquoteright}s main sink) and its trend. Our inversion solves the Bayesian optimization problem analytically including closed-form characterization of errors. This allows us to (1)\ quantify the information content from the inversion towards optimizing methane emissions and its trends, (2)\ diagnose error correlations between constraints on emissions and OH concentrations, and (3)\ generate a large ensemble of solutions testing different assumptions in the inversion. We show how the analytical approach can be used, even when prior error standard deviation distributions are lognormal. Inversion results show large overestimates of Chinese coal emissions and Middle East oil and gas emissions in the EDGAR v4.3.2 inventory but little error in the United States where we use a new gridded version of the EPA national greenhouse gas inventory as prior estimate. Oil and gas emissions in the EDGAR v4.3.2 inventory show large differences with national totals reported to the United Nations Framework Convention on Climate Change (UNFCCC), and our inversion is generally more consistent with the UNFCCC data. The observed 2010{\textendash}2015 growth in atmospheric methane is attributed mostly to an increase in emissions from India, China, and areas with large tropical wetlands. The contribution from OH trends is small in comparison. We find that the inversion provides strong independent constraints on global methane emissions (546 Tg a-1) and global mean OH concentrations (atmospheric methane lifetime against oxidation by tropospheric OH of\ 10.8{\textpm}0.4\ years), indicating that satellite observations of atmospheric methane could provide a proxy for OH concentrations in the future.}, url = {https://doi.org/10.5194/acp-19-7859-2019}, author = {Joannes D. Maasakkers and Daniel J. Jacob and Melissa P. Sulprizio and Tia R. Scarpelli and Hannah Nesser and Sheng, Jian-Xiong and Zhang, Yuzhong and Monica Hersher and A. Anthony Bloom and Kevin W. Bowman and John R. Worden and Greet Janssens-Maenhout and Robert J. Parker} } @article {635190, title = {Bottom-Up Estimates of Coal Mine Methane Emissions in China: A Gridded Inventory, Emission Factors, and Trends}, journal = {Environmental Science and Technology Letters}, year = {2019}, abstract = {China has large but uncertain coal mine methane (CMM) emissions. Inverse modeling (top-down) analyses of atmospheric methane observations can help improve the emission estimates but require reliable emission patterns as prior information. To serve this urgent need, we developed a high-resolution (0.25{\textdegree} {\texttimes} 0.25{\textdegree}) methane emission inventory for China{\textquoteright}s coal mining using a recent publicly available database of more than 10000 coal mines in China for 2011. This number of coal mines is 25 and 2.5 times, respectively, more than the number available in the EDGAR v4.2 and EDGAR v4.3.2 gridded global inventories, which have been extensively used in past inverse analyses. Our inventory shows large differences with the EDGAR v4.2 as well as its more recent version, EDGAR v4.3.2. Our results suggest that China{\textquoteright}s CMM emissions have been decreasing since 2012 on the basis of coal mining activities and assuming time-invariant emission factors but that regional trends differ greatly. Use of our inventory as prior information in future inverse modeling analyses can help better quantify CMM emissions as well as more confidently guide the future mitigation of coal to gas in China.}, url = {https://pubs.acs.org/doi/abs/10.1021/acs.estlett.9b00294}, author = {Sheng, Jianxiong and Shaojie Song and Zhang, Yuzhong and Ronald G. Prinn and Greet Janssens-Maenhout} } @article {621678, title = {Satellite-observed changes in Mexico{\textquoteright}s offshore gas flaring activitylinked to oil/gas regulations}, journal = {Geophysical Research Letters}, year = {2019}, abstract = {Gas flaring is a commonly-used practice in the oil and gas sector that leads to key air pollutant and greenhouse gas emissions. Here we use multi-pollutant (NO2, SO2) satellite observations from 2005{\textendash}2017 to quantify gas flaring activity in Mexico{\textquoteright}s offshore production cluster, which produces ~50{\textendash}70\% of the country{\textquoteright}s oil and is among the world{\textquoteright}s largest oil fields. We estimate annual flared-gas-volume ranging from 5.5{\textendash}20{\texttimes}109m3\ over the Mexican offshore corresponding to \> 40\% associated gas production, which is significantly larger than for instance offshore US where reportedly \<3\% of associated gas is flared. The 13-year record of satellite-derived gas flaring indicates a drastic increase until 2008 and a decline afterwards. While the increased flaring is associated with efforts to enhance oil production, the post-2008 decline is linked to an expanding capacity of associated gas utilization, providing a continuing opportunity to reduce flaring for environmental and economic benefits.}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081145}, author = {Zhang, Yuzhong and Ritesh Gautam and Zavala-Araiza, Daniel and Daniel J. Jacob and Zhang, Ruixiong and Lei Zhu and Sheng, Jian-Xiong and Tia Scarpelli} } @article {622566, title = {Possible heterogeneous hydroxymethanesulfonate (HMS) chemistry in northern China winter haze and implications for rapid sulfate formation}, journal = {Atmospheric Chemistry and Physics}, volume = {19}, year = {2019}, pages = {1357-1371}, abstract = {The chemical mechanisms responsible for rapid sulfate production, an important driver of winter haze formation in northern China, remain unclear. Here, we propose a potentially important heterogeneous hydroxymethanesulfonate (HMS) chemical mechanism. Through analyzing field measurements with aerosol mass spectrometry, we show evidence for a possible significant existence in haze aerosols of organosulfur primarily as HMS, misidentified as sulfate in previous observations. We estimate that HMS can account for up to about one-third of the sulfate concentrations unexplained by current air quality models. Heterogeneous production of HMS by\ SO2\ and formaldehyde is favored under northern China winter haze conditions due to high aerosol water content, moderately acidic pH values, high gaseous precursor levels, and low temperature. These analyses identify an unappreciated importance of formaldehyde in secondary aerosol formation and call for more research on sources and on the chemistry of formaldehyde in northern China winter.}, url = {https://www.atmos-chem-phys.net/19/1357/2019/acp-19-1357-2019.html}, author = {Shaojie Song and Meng Gao and Weiqi Xu and Yele Sun and Douglas R. Worsnop and John T. Jayne and Zhang, Yuzhong and Lei Zhu and Mei Li and Zhen Zhou and Chunlei Cheng and Yibing Lv and Ying Wang and Wei Peng and Xiaobin Xu and Nan Lin and Yuxuan Wang and Shuxiao Wang and J. William Munger and Daniel Jacob and Michael B. McElroy} } @article {609570, title = {Comparative analysis of low-Earth orbit (TROPOMI) and geostationary (GeoCARB, GEO-CAPE) satellite instruments for constraining methane emissions on fine regional scales: application to the Southeast US}, journal = {Atmos. Meas. Tech.}, volume = {11}, year = {2018}, pages = {6379-6388}, abstract = {We conduct observing system simulation experiments (OSSEs) to determine the potential of future satellite measurements of atmospheric methane columns (TROPOMI, GeoCARB, GEO-CAPE) for constraining methane emissions down to the 25 km scale through inverse analyses. The OSSE uses the GEOS-Chem chemical transport model (0.25{\textopenbullet} {\texttimes} 0.3125{\textopenbullet} grid resolution) in a 1-week simulation for the Southeast US with 216 emission elements to be optimized through inversion 5 of synthetic satellite observations. Clouds contaminate 73-91\% of the viewing scenes depending on pixel size. Comparison of GEOS-Chem to TCCON surface-based methane column observations indicates a model transport error standard deviation of 12 ppb, larger than the instrument errors when aggregated on the 25 km model grid scale, and with a temporal error correlation of 6 hours. We find that TROPOMI (7{\texttimes}7 km2 pixels, daily return time) can provide a coarse regional optimization of methane emissions, and is highly sensitive to cloud cover. The geostationary instruments can do much better and are less 10 sensitive to cloud cover, reflecting both their finer pixel resolution and more frequent observations. The information content from GeoCARB toward constraining methane emissions increases by 20-25\% for each doubling of the GeoCARB measurement frequency. Temporal error correlation in the transport model moderates but does not cancel the benefit of more frequent measurements for geostationary instruments.}, url = {https://doi.org/10.5194/amt-11-6379-2018}, author = {Sheng, J.-X. and D.J. Jacob and J.D. Maasakkers and Y. Zhang and M.P. Sulprizio} } @article {613219, title = {Estimator of surface ozone using formaldehyde and carbon monoxide concentrations over the eastern United States in summer}, journal = {Journal of Geophysical Research: Atmospheres}, year = {2018}, abstract = {Strong correlations of O3-CH2O, O3-CO and CO-CH2O were observed during the DISCOVER-AQ aircraft experiment in July 2011 over the Washington-Baltimore area. The linear regression slopes of observed O3-CH2O, O3-CO and CO-CH2O do not vary significantly with time (11 A.M. to 4 P.M.) or altitude in the boundary layer. These observed relationships are simulated well by a regional chemical transport model. Using tagged-tracer simulations, we find that biogenic isoprene oxidation makes the largest contribution to the regression slope of O3-CH2O across much of the eastern United States, providing a good indicator for O3\ enhanced by biogenic isoprene oxidation. In contrast, the regression slope of O3-CO is controlled by both anthropogenic and biogenic emissions. Therefore, we use the CO-CH2O relationship to separate biogenic from anthropogenic contributions to CO. By combining these regressions, we can track the contributions to surface O3\ by anthropogenic and biogenic factors and build a fast-response ozone estimator using near surface CH2O and CO concentrations as inputs. We examine the quality of O3\ estimator by increasing or decreasing anthropogenic emissions by up to 50\%. The estimated O3\ distribution is in reasonably good agreement with the full-model simulations (R2\ \>0.77 in the range of -30\% to +50\% of anthropogenic emissions). The analysis provides the basis for using high-quality geostationary satellites with UV, thermal infrared, or near infrared instruments for observing CH2O and CO to improve surface O3\ distribution monitoring. The estimation model can also be applied to derive observation-derived regional metrics to evaluate and improve full-fledged 3-D air quality models.}, url = {https://doi.org/10.1029/2018JD028452}, author = {Cheng, Ye and Wang, Yuhang and Zhang, Yuzhong and James H Crawford and Glenn S Diskin and Weinheimer, Andrew J and Alan Fried} } @article {605595, title = {Improve Observation-based Ground-level Ozone Spatial Distribution by Compositing Satellite and Surface Observations: A Simulation Experiment}, journal = {Atmospheric Environment}, volume = {180}, year = {2018}, pages = {226-233}, abstract = {Obtaining the full spatial coverage of daily surface ozone fields is challenging because of the sparsity of the surface monitoring network and the difficulty in direct satellite retrievals of surface ozone. We propose an indirect satellite retrieval framework to utilize the information from satellite-measured column densities of tropospheric NO2 and CH2O, which are sensitive to the lower troposphere, to derive surface ozone fields. The method is applicable to upcoming geostationary satellites with high-quality NO2 and CH2O measurements. To prove the concept, we conduct a simulation experiment using a 3-D chemical transport model for July 2011 over the eastern US. The results show that a second order regression using both NO2 and CH2O column densities can be an effective predictor for daily maximum 8-hour average ozone. Furthermore, this indirect retrieval approach is shown to be complementary to spatial interpolation of surface observations, especially in regions where the surface sites are sparse. Combining column observations of NO2 and CH2O with surface site measurements leads to an improved representation of surface ozone over simple kriging, increasing the R2 value from 0.53 to 0.64 at a surface site distance of 252 km. The improvements are even more significant with larger surface site distances. The simulation experiment suggests that the indirect satellite retrieval technique can potentially be a useful tool to derive the full spatial coverage of daily surface ozone fields if satellite observation uncertainty is moderate.}, url = {https://doi.org/10.1016/j.atmosenv.2018.02.044}, author = {Zhang, Yuzhong and Wang, Yuhang and Crawford, James and Cheng, Ye and Jianfeng Li} } @article {609569, title = {Monitoring global OH concentrations using satellite observations of atmospheric methane}, journal = {Atmospheric Chemistry and Physics}, volume = {18}, number = {21}, year = {2018}, pages = {15959-15973}, abstract = {The hydroxyl radical (OH) is the main tropospheric oxidant and is the largest sink for atmospheric methane. The global abundance of OH has been monitored for the past decades with the methyl chloroform (CH3CCl3) proxy. This approach is becoming ineffective as atmospheric CH3CCl3 concentrations decline. Here we propose that satellite observations of atmospheric methane in the shortwave infrared (SWIR) and thermal infrared (TIR) can provide an effective replacement method. The premise is that the atmospheric signature of the methane sink from oxidation by OH is distinct from that of methane emissions. We evaluate this method in an observing system simulation experiment (OSSE) framework using synthetic SWIR and TIR satellite observations representative of the TROPOMI and CrIS instruments, respectively. The synthetic observations are interpreted with a Bayesian inverse analysis optimizing both gridded methane emissions and global OH concentrations with detailed error accounting, including errors in meteorological fields and in OH distributions. We find that the satellite observations can constrain the global tropospheric OH concentrations with a precision better than 1\% and an accuracy of about 3\% for SWIR and 7\% for TIR. The inversion can successfully separate contributions from methane emissions and OH concentrations to the methane budget and its trend. We also show that satellite methane observations can constrain the interhemispheric difference in OH. The main limitation to the accuracy is uncertainty in the spatial and seasonal distribution of OH.}, url = {https://doi.org/10.5194/acp-18-15959-2018}, author = {Zhang, Yuzhong and Daniel J. Jacob and Joannes D. Maasakkers and Melissa P. Sulprizio and Sheng, Jian-Xiong and Ritesh Gautam and John Worden} } @article {GRL:GRL56104, title = {Large biogenic contribution to boundary layer O3-CO regression slope in summer}, journal = {Geophysical Research Letters}, volume = {40}, year = {2017}, note = {2017GL074405}, abstract = {Strong correlation between O3 and CO was observed during the DISCOVER-AQ aircraft experiment in July 2011 over the Washington-Baltimore area. The observed correlation does not vary significantly with time or altitude in the boundary layer. The observations are simulated well by a regional chemical transport model. We analyze the model results to understand the factors contributing to the observed O3-CO regression slope, which has been used in past studies to estimate the anthropogenic O3 production amount. We trace separately four different CO sources: primary anthropogenic emissions, oxidation of anthropogenic volatile organic compounds (VOCs), oxidation of biogenic isoprene, and transport from the lateral and upper model boundaries. Modeling analysis suggests that the contribution from biogenic isoprene oxidation to the observed O3-CO regression slope is as large as that from primary anthropogenic CO emissions. As a result of decrease of anthropogenic primary CO emissions during the past decades, biogenic CO from oxidation of isoprene is increasingly important. Consequently, observed and simulated O3-CO regression slopes can no longer be used directly with an anthropogenic CO emission inventory to quantify anthropogenic O3 production over the United States. The consistent enhancement of O3 relative to CO observed in the boundary layer, as indicated by the O3-CO regression slope, provides a useful constraint on model photochemistry and emissions.}, keywords = {biogenic, Boundary layer processes, Carbon Monoxide, formaldehyde, isoprene, Ozone, Photochemistry, regression slope, Troposphere: composition and chemistry, Troposphere: constituent transport and chemistry}, issn = {1944-8007}, doi = {10.1002/2017GL074405}, url = {http://dx.doi.org/10.1002/2017GL074405}, author = {Cheng, Ye and Wang, Yuhang and Zhang, Yuzhong and Chen, Gao and Crawford, James H. and Kleb, Mary M. and Diskin, Glenn S. and Weinheimer, Andrew J.} } @article {635995, title = {Improving PM2.5 Air Quality Model Forecasts in China Using a Bias-Correction Framework}, journal = {Atmosphere}, volume = {8}, number = {8}, year = {2017}, pages = {147}, abstract = {Chinese cities are experiencing severe air pollution in particular, with extremely high PM2.5\ levels observed in cold seasons. Accurate forecasting of occurrence of such air pollution events in advance can help the community to take action to abate emissions and would ultimately benefit the citizens. To improve the PM2.5\ air quality model forecasts in China, we proposed a bias-correction framework that utilized the historic relationship between the model biases and forecasted and observational variables to post-process the current forecasts. The framework consists of four components: (1) a feature selector that chooses the variables that are informative to model forecast bias based on historic data; (2) a classifier trained to efficiently determine the forecast analogs (clusters) based on clustering analysis, such as the distance-based method and the classification tree, etc.; (3) an error estimator, such as the Kalman filter, to predict model forecast errors at monitoring sites based on forecast analogs; and (4) a spatial interpolator to estimate the bias correction over the entire modeling domain. One or more methods were tested for each step. We applied five combinations of these methods to PM2.5\ forecasts in 2014{\textendash}2016 over China from the operational AiMa air quality forecasting system using the Community Multiscale Air Quality (CMAQ) model. All five methods were able to improve forecast performance in terms of normalized mean error (NME) and root mean square error (RMSE), though to a relatively limited degree due to the rapid changing of emission rates in China. Among the five methods, the CART-LM-KF-AN (a Classification And Regression Trees-Linear Model-Kalman Filter-Analog combination) method appears to have the best overall performance for varied lead times. While the details of our study are specific to the forecast system, the bias-correction framework is likely applicable to the other air quality model forecast as well.}, url = {https://doi.org/10.3390/atmos8080147}, author = {Baolei Lyu and Zhang, Yuzhong and Hu, Yongtao} } @article {zou2017arctic, title = {Arctic sea ice, Eurasia snow, and extreme winter haze in China}, journal = {Science Advances}, volume = {3}, number = {3}, year = {2017}, pages = {e1602751}, publisher = {American Association for the Advancement of Science}, abstract = {The East China Plains (ECP) region experienced the worst haze pollution on record for January in 2013. We show that the unprecedented haze event is due to the extremely poor ventilation conditions, which had not been seen in the preceding three decades. Statistical analysis suggests that the extremely poor ventilation conditions are linked to Arctic sea ice loss in the preceding autumn and extensive boreal snowfall in the earlier winter. We identify the regional circulation mode that leads to extremely poor ventilation over the ECP region. Climate model simulations indicate that boreal cryospheric forcing enhances the regional circulation mode of poor ventilation in the ECP region and provides conducive conditions for extreme haze such as that of 2013. Consequently, extreme haze events in winter will likely occur at a higher frequency in China as a result of the changing boreal cryosphere, posing difficult challenges for winter haze mitigation but providing a strong incentive for greenhouse gas emission reduction.}, url = {http://advances.sciencemag.org/content/3/3/e1602751}, author = {Zou, Yufei and Wang, Yuhang and Zhang, Yuzhong and Koo, Ja-Ho} } @article {zhang2017enhanced, title = {Enhanced trans-Himalaya pollution transport to the Tibetan Plateau by cut-off low systems}, journal = {Atmospheric Chemistry and Physics}, volume = {17}, number = {4}, year = {2017}, pages = {3083{\textendash}3095}, publisher = {Copernicus GmbH}, abstract = {Long-range\ transport followed by deposition of black carbon on glaciers of Tibet is one of the key issues of climate research as it induces changes on radiative forcing and subsequently impacting the melting of glaciers. The transport mechanism, however, is not well understood. In this study, we use short-lived reactive aromatics as proxies to diagnose transport of pollutants to Tibet. In situ observations of short-lived reactive aromatics across the Tibetan Plateau are analyzed using a regional chemistry and transport model. The model performance using the current emission inventories over the region is poor due to problems in the inventories and model transport. Top-down\ emissions constrained by satellite observations of glyoxal are a factor of 2{\textendash}6 higher than the a priori emissions over the industrialized Indo-Gangetic Plain. Using the top-down emissions, agreement between model simulations and surface observations of aromatics improves. We find enhancements of reactive aromatics over Tibet by a factor of 6 on average due to rapid transport from India and nearby regions during the presence of a high-altitude cut-off low system. Our results suggest that the cut-off low system is a major pathway for long-range transport of pollutants such as black carbon. The modeling analysis reveals that even the state-of-the-science high-resolution reanalysis cannot simulate this cut-off low system accurately, which probably explains in part the underestimation of black carbon deposition over Tibet in previous modeling studies. Another model deficiency of underestimating pollution transport from the south is due to the complexity of terrain, leading to enhanced transport. It is therefore challenging for coarse-resolution global climate models to properly represent the effects of long-range transport of pollutants on the Tibetan environment and the subsequent consequence for regional climate forcing.}, url = {http://www.atmos-chem-phys.net/17/3083/2017/acp-17-3083-2017.html}, author = {Zhang, Ruixiong and Wang, Yuhang and He, Qiusheng and Chen, Laiguo and Zhang, Yuzhong and Qu, Hang and Smeltzer, Charles and Jianfeng Li and Alvarado, Leonardo and Vrekoussis, Mihalis and others} } @article {zhang2017top, title = {Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere}, journal = {Nature Geoscience}, year = {2017}, publisher = {Springer Nature}, abstract = { [[{"fid":"605511","view_mode":"default","type":"media","attributes":{"height":"308","width":"371","alt":"enhanced brown carbon at high altitudes","class":"media-element file-default "}}]] Carbonaceous aerosols affect the global radiative balance by absorbing and scattering radiation, which leads to warming or cooling of the atmosphere, respectively. Black carbon is the main light-absorbing component. A portion of the organic aerosol known as brown carbon also absorbs light. The climate sensitivity to absorbing aerosols rapidly increases with altitude, but brown carbon measurements are limited in the upper troposphere. Here we present aircraft observations of vertical aerosol distributions over the continental United States in May and June 2012 to show that light-absorbing brown carbon is prevalent in the troposphere, and absorbs more short-wavelength radiation than black carbon at altitudes between 5 and 12 km. We find that brown carbon is transported to these altitudes by deep convection, and that in-cloud heterogeneous processing may produce brown carbon. Radiative transfer calculations suggest that brown carbon accounts for about 24\% of combined black and brown carbon warming effect at the tropopause. Roughly two-thirds of the estimated brown carbon forcing occurs above 5 km, although most brown carbon is found below 5 km. The highest radiative absorption occurred during an event that ingested a wildfire plume. We conclude that high-altitude brown carbon from biomass burning is an unappreciated component of climate forcing. }, author = {Zhang, Yuzhong and Forrister, Haviland and Liu, Jiumeng and Dibb, Jack E and Anderson, Bruce and Schwarz, Joshua P and Perring, Anne E and Jimenez, Jose L and Pedro Campuzano-Jost and Wang, Yuhang and others} } @article {liu2016agricultural, title = {Agricultural Fires in the Southeastern US during SEAC4RS: Emissions of Trace Gases and Particles and Evolution of Ozone, Reactive Nitrogen, and Organic Aerosol}, journal = {Journal of Geophysical Research: Atmospheres}, year = {2016}, publisher = {Wiley Online Library}, abstract = {Emissions from 15 agricultural fires in the southeastern U.S. were measured from the NASA DC-8 research aircraft during the summer 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. This study reports a detailed set of emission factors (EFs) for 25 trace gases and 6 fine particle species. The chemical evolution of the primary emissions in seven plumes was examined in detail for ~1.2 h. A Lagrangian plume cross-section model was used to simulate the evolution of ozone (O3), reactive nitrogen species, and organic aerosol (OA). Observed EFs are generally consistent with previous measurements of crop residue burning, but the fires studied here emitted high amounts of SO2\ and fine particles, especially primary OA and chloride. Filter-based measurements of aerosol light absorption implied that brown carbon (BrC) was ubiquitous in the plumes. In aged plumes, rapid production of O3, peroxyacetyl nitrate (PAN), and nitrate was observed with ΔO3/ΔCO, ΔPAN/ΔNOy, and Δnitrate/ΔNOy\ reaching ~0.1, ~0.3, and ~0.3. For five selected cases, the model reasonably simulated O3\ formation but underestimated PAN formation. No significant evolution of OA mass or BrC absorption was observed. However, a consistent increase in oxygen-to-carbon (O/C) ratios of OA indicated that OA oxidation in the agricultural fire plumes was much faster than in urban and forest fire plumes. Finally, total annual SO2, NOx, and CO emissions from agricultural fires in Arkansas, Louisiana, Mississippi, and Missouri were estimated (within a factor of ~2) to be equivalent to ~2\% SO2\ from coal combustion and ~1\% NOx\ and ~9\% CO from mobile sources.}, url = {http://onlinelibrary.wiley.com/doi/10.1002/2016JD025040/full}, author = {Liu, X. and Y. Zhang and Huey, L. G. and Yokelson, RJ and Y. Wang, and Jimenez, J. L. and Campuzano-Jost, P and Beyersdorf, AJ and Blake, DR and Choi, Y and others} } @article {zhang2016climate, title = {Climate-driven ground-level ozone extreme in the fall over the Southeast United States}, journal = {Proceedings of the National Academy of Sciences}, year = {2016}, pages = {201602563}, publisher = {National Acad Sciences}, abstract = { [[{"fid":603811,"view_mode":"default","type":"media","attributes":{"height":"281","width":"339","alt":"LongTerm Ozone Trend","class":"media-element file-default"}}]] Ground-level ozone is adverse to human and vegetation health. High ground-level ozone concentrations usually occur over the United States in the summer, often referred to as the ozone season. However, observed monthly mean ozone concentrations in the southeastern United States were higher in October than July in 2010. The October ozone average in 2010 reached that of July in the past three decades (1980{\textendash}2010). Our analysis shows that this extreme October ozone in 2010 over the Southeast is due in part to a dry and warm weather condition, which enhances photochemical production, air stagnation, and fire emissions. Observational evidence and modeling analysis also indicate that another significant contributor is enhanced emissions of biogenic isoprene, a major ozone precursor, from water-stressed plants under a dry and warm condition. The latter finding is corroborated by recent laboratory and field studies. This climate-induced biogenic control also explains the puzzling fact that the two extremes of high October ozone both occurred in the 2000s when anthropogenic emissions were lower than the 1980s and 1990s, in contrast to the observed decreasing trend of July ozone in the region. The occurrences of a drying and warming fall, projected by climate models, will likely lead to more active photochemistry, enhanced biogenic isoprene and fire emissions, an extension of the ozone season from summer to fall, and an increase of secondary organic aerosols in the Southeast, posing challenges to regional air quality management. }, url = {http://www.pnas.org/content/113/36/10025.abstract}, author = {Zhang, Yuzhong and Wang, Yuhang} } @article {gu2016inverse, title = {Inverse modelling of NO x emissions over eastern China: uncertainties due to chemical non-linearity}, journal = {Atmospheric Measurement Techniques}, volume = {9}, number = {10}, year = {2016}, pages = {5193}, publisher = {Copernicus GmbH}, abstract = {Satellite observations of nitrogen dioxide (NO2) have often been used to derive nitrogen oxides (NOx = NO + NO2) emissions. A widely used inversion method was developed by Martin et al.\ (2003). Refinements of this method were subsequently developed. In the context of this inversion method, we show that the local derivative (of a first-order Taylor expansion) is more appropriate than the {\textquotedblleft}bulk ratio{\textquotedblright} (ratio of emission to column) used in the original formulation for polluted regions. Using the bulk ratio can lead to biases in regions of high NOx\ emissions such as eastern China due to chemical non-linearity. Inverse modelling using the local derivative method is applied to both GOME-2 and OMI satellite measurements to estimate anthropogenic NOx\ emissions over eastern China. Compared with the traditional method using bulk ratio, the local derivative method produces more consistent NOx\ emission estimates between the inversion results using GOME-2 and OMI measurements. The results also show significant changes in the spatial distribution of NOx\ emissions, especially over high emission regions of eastern China. We further discuss a potential pitfall of using the difference of two satellite measurements to derive NOx\ emissions. Our analysis suggests that chemical non-linearity needs to be accounted for and that a careful bias analysis is required in order to use the satellite differential method in inverse modelling of NOx\ emissions.}, url = {http://www.atmos-meas-tech.net/9/5193/2016/}, author = {Gu, Dasa and Wang, Yuhang and Yin, Ran and Zhang, Yuzhong and Smeltzer, Charles} } @article {zhang2016large, title = {Large vertical gradient of reactive nitrogen oxides in the boundary layer: Modeling analysis of DISCOVER-AQ 2011 observations}, journal = {Journal of Geophysical Research: Atmospheres}, year = {2016}, publisher = {Wiley Online Library}, abstract = { [[{"fid":"605516","view_mode":"default","type":"media","attributes":{"style":"width: 300px; height: 268px;","alt":"NOx gradient in the PBL","class":"media-element file-default "}}]] An often used assumption in air pollution studies is a well-mixed boundary layer (BL), where pollutants are evenly distributed. Because of the difficulty in obtaining vertically resolved measurements, the validity of the assumption has not been thoroughly evaluated. In this study, we use more than 200 vertical profiles observed in the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) aircraft campaign in July 2011 to examine the vertical distributions of pollutants over the Washington-Baltimore area. While many long-lived species are well mixed in daytime, the observed average vertical profile of NOx\ shows a large negative gradient with increasing altitude in the BL. Our analysis suggests that the magnitude of the NOxgradient is highly sensitive to atmospheric stability. We investigate how parameterizations of the BL and land-surface processes impact vertical profiles in a 1-D chemical transport model, using three BL schemes (Asymmetric Convective Model version 2 (ACM2), Yonsei University (YSU), and Mellor-Yamada-Janjic (MYJ)) and two land-surface schemes (Noah and Rapid Update Cycle (RUC)). The model reasonably reproduces the median vertical profiles of NOx\ under different BL stability conditions within 30\% of observations, classified based on potential temperature gradient and BL height. Comparisons with NOx\ observations for individual vertical profiles reveal that while YSU performs better in the turbulent and deep BL case, in general, ACM2 (RMSE = 2.0 ppbv) outperforms YSU (RMSE = 2.5 ppbv) and MYJ (RMSE = 2.2 ppbv). Results also indicate that the land-surface schemes in the Weather Research and Forecasting (WRF) model have a small impact on the NOx\ gradient. Using model simulations, we analyze the impact of BL NOx\ gradient on the calculation of the ozone production rate and satellite NO2retrieval. We show that using surface measurements and the well-mixed BL assumption causes a ~45\% high bias in the estimated BL ozone production rate and that the variability of NO2\ vertical profiles is responsible for 5{\textendash}10\% variability in the retrieved NO2\ tropospheric vertical columns. }, url = {http://onlinelibrary.wiley.com/doi/10.1002/2015JD024203/full}, author = {Zhang, Yuzhong and Wang, Yuhang and Chen, Gao and Smeltzer, Charles and Crawford, James and Olson, Jennifer and Szykman, James and Weinheimer, Andrew J and Knapp, David J and Montzka, Denise D and others} } @article {zhang2014surface, title = {Surface and free tropospheric sources of methanesulfonic acid over the tropical Pacific Ocean}, journal = {Geophysical Research Letters}, volume = {41}, number = {14}, year = {2014}, pages = {5239{\textendash}5245}, publisher = {Wiley Online Library}, abstract = { [[{"fid":"605531","view_mode":"default","type":"media","attributes":{"style":"width: 300px; height: 205px;","alt":"MSA chemistry","class":"media-element file-default "}}]] The production of sulfate aerosols through sulfur chemistry in marine environments is critical to the tropical climate system. However, not all sulfur compounds have been studied in detail. One such compound is methanesulfonic acid (MSA). In this study, we use a one-dimensional chemical transport model to analyze the observed vertical profiles of gas phase MSA during the Pacific Atmospheric Sulfur Experiment. The observed sharp decrease in MSA from the surface to 600 m implies a surface source of 4.0 {\texttimes} 107\ molecules/cm2/s. Evidence suggests that this source is photolytically enhanced in daytime. We also find that the observed large increase of MSA from the boundary layer into the lower free troposphere (1000{\textendash}2000 m) results mainly from the degassing of MSA from dehydrated aerosols. We estimate a source of 1.2 {\texttimes} 107\ molecules/cm2/s to the free troposphere through this pathway. This source of soluble MSA could potentially provide an important precursor for new particle formation in the free troposphere over the tropics, affecting the climate system through aerosol-cloud interactions. }, url = {http://onlinelibrary.wiley.com/doi/10.1002/2014GL060934/full}, author = {Zhang, Yuzhong and Wang, Yuhang and Gray, Burton Alonza and Gu, Dasa and Mauldin, Lee and Cantrell, Christopher and Bandy, Alan} } @article {wang2013properties, title = {Properties and inflammatory effects of various size fractions of ambient particulate matter from Beijing on A549 and J774A. 1 cells}, journal = {Environmental science \& technology}, volume = {47}, number = {18}, year = {2013}, pages = {10583{\textendash}10590}, publisher = {ACS Publications}, abstract = { [[{"fid":"605491","view_mode":"default","type":"media","attributes":{"height":"500","width":"499","alt":"cell toxicity","class":"media-element file-default"}}]] Particulate matter (PM) is a major ambient air pollutant causing millions of premature deaths each year in China. The toxicity of PM is property and size dependent. In this study, ambient PM samples collected in Beijing were divided into five size fractions with nominal aerodynamic ranges of \<0.40, 0.40{\textendash}1.1, 1.1{\textendash}3.3, 3.3{\textendash}5.8, and 5.8{\textendash}10 μm. Individual size fractions were characterized for a number of properties including particle size distribution, specific surface area, zeta potential, dithiothreitol (DTT)-based redox ability, and contents of water-soluble organic carbon (WSOC), polycyclic aromatic hydrocarbons (PAHs), selected metals, and endotoxin. Human adenocarcinomic alveolar epithelial cell line A549 and small mouse monocyte-macrophage cell line J774A.1 were tested for their relative viabilities and inflammatory effects (interleukine-8 for A549 and tumor necrosis factor-α for J774A.1) after exposure to PM of various sizes. It was found that PM specific area was positively correlated with WSOC, high molecular weight PAHs, DTT-based redox ability, negatively correlated with surface zeta potential and lithophile metals. Several trace metals from combustion sources were enriched in intermediate size fractions. For both endotoxin concentrations of the PM and PM induced inflammatory cytokine expressions by the two cell lines, there were general increasing trends as PM size increased with an exception of the finest fraction, which induced the highest inflammatory effects. It seems that the size dependence of cytokine expression was associated with a number of properties including endotoxin content, zeta potential, settling velocity, metal content, and DTT-based redox ability. }, url = {http://pubs.acs.org/doi/abs/10.1021/es401394g}, author = {Wang, Bin and Li, Kexin and Jin, Wenjie and Lu, Yan and Zhang, Yuzhong and Shen, Guofeng and Wang, Rong and Shen, Huizhong and Li, Wei and Huang, Ye and others} } @article {zhang2011passive, title = {A passive air sampler for characterizing the vertical concentration profile of gaseous phase polycyclic aromatic hydrocarbons in near soil surface air}, journal = {Environmental Pollution}, volume = {159}, number = {3}, year = {2011}, pages = {694{\textendash}699}, publisher = {Elsevier}, abstract = {Air{\textendash}soil exchange is an important process governing the fate of polycyclic aromatic hydrocarbons (PAHs). A novel passive air sampler was designed and tested for measuring the vertical concentration profile of 4 low molecular weight PAHs in gaseous phase (PAHLMW4) in near soil surface air. Air at various heights from 5 to 520\ mm above the ground was sampled by polyurethane foam disks held in down-faced cartridges. The samplers were tested at three sites: A: an extremely contaminated site, B: a site near A, and C: a background site on a university campus. Vertical concentration gradients were revealed for PAHLMW4\ within a thin layer close to soil surface at the three sites. PAH concentrations either decreased (Site A) or increased (Sites B and C) with height, suggesting either deposition to or evaporation from soils. The sampler is a useful tool for investigating air{\textendash}soil exchange of gaseous phase semi-volatile organic chemicals.}, url = {http://www.sciencedirect.com/science/article/pii/S026974911000566X}, author = {Zhang, Yuzhong and Deng, Shuxing and Liu, Yanan and Shen, Guofeng and Li, Xiqing and Cao, Jun and Wang, Xilong and Reid, Brian and Tao, Shu} }