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Publications

2020
Ruixiong Zhang, Yuzhong Zhang, Haipeng Lin, Xu Feng, Tzung-May Fu, and Yuhang Wang. 4/24/2020. “NOx Emission Reduction and Recovery during COVID-19 in East China.” Atmosphere, 11, Pp. 433. Publisher's VersionAbstract
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.
Yuzhong Zhang, Ritesh Gautam, Sudhanshu Pandey, Mark Omara, Joannes D. Maasakkers, Pankaj Sadavarte, David Lyon, Hannah Nesser, Melissa P. Sulprizio, Daniel J. Varon, Ruixiong Zhang, Sander Houweling, Daniel Zavala-Araiza, Ramon A. Alvarez, Alba Lorente, Steven P. Hamburg, Ilse Aben, and Daniel J. Jacob. 4/22/2020. “Quantifying methane emissions from the largest oil-producing basin in the United States from space.” Science Advances, 6. Publisher's VersionAbstract
Using new satellite observations and atmospheric inverse modeling, we report methane emissions from the Permian Basin, which is among the world’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 ± 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–based atmospheric inversion framework, providing a robust top-down analytical tool for quantifying and evaluating subregional methane emissions.
Meng Gao, Jinhui Gao, Bin Zhu, Rajesh Kumar, Xiao Lu, Shaojie Song, Yuzhong Zhang, Beixi Jia, Peng Wang, Gufran Beig, Jianlin Hu, Qi Ying, Hongliang Zhang, Peter Sherman, and Michael B. McElroy. 4/16/2020. “Ozone Pollution over China and India: Seasonality and Sources.” Atmospheric Chemistry and Physics, 20, 7, Pp. 4399–4414. Publisher's VersionAbstract
A regional fully coupled meteorology–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.
Xiao Lu, Lin Zhang, Xiaolin Wang, Meng Gao, Ke Li, Yuzhong Zhang, Xu Yue, and Yuanhang Zhang. 3/18/2020. “Rapid increases in warm-season surface ozone and resulting health impact over China since 2013.” Environmental Science & Technology Letters, 7, Pp. 240-247. Publisher's VersionAbstract
China’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–September) surface ozone trends and resulting health impacts at Chinese cities in 2013–2019. 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–1, with over 90% of the sites showing positive trends and 30% with trends larger than 3.0 ppb year–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–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.
Aoxing Zhang, Yuhang Wang, Yuzhong Zhang, Rodney J. Weber, Yongjia Song, Ziming Ke, and Yufei Zou. 2020. “Modeling the global radiative effect of brown carbon: a potentially larger heating source in the tropical free troposphere than black carbon.” Atmos. Chem. Phys. , 20, Pp. 1901–1920. Publisher's VersionAbstract
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.
2019
Shaojie Song, Athanasios Nenes, Meng Gao, Yuzhong Zhang, Pengfei Liu, Jingyuan Shao, Dechao Ye, Weiqi Xu, Lu Lei, Yele Sun, Baoxian Liu, Shuxiao Wang, and Michael B. McElroy. 11/4/2019. “Thermodynamic Modeling Suggests Declines in Water Uptake and Acidity of Inorganic Aerosols in Beijing Winter Haze Events during 2014/2015−2018/2019.” Environmental Science and Technology Letters. Publisher's VersionAbstract
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%–17% due to changes in aerosol compositions (more nitrate and less sulfate and chloride) and the modeled pH increased by about 0.3–0.4 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.
Shixian Zhai, Daniel J. Jacob, Xuan Wang, Lu Shen, Ke Li, Yuzhong Zhang, Ke Gui, Tianliang Zhao, and Hong Liao. 8/2019. “Fine particulate matter (PM2.5) trends in China, 2013-2018: separating contributions from anthropogenic emissions and meteorology.” Atmos. Chem. Phys. , 19, Pp. 11031–11041. Publisher's Version
Joannes D. Maasakkers, Daniel J. Jacob, Melissa P. Sulprizio, Tia R. Scarpelli, Hannah Nesser, Jian-Xiong Sheng, Yuzhong Zhang, Monica Hersher, A. Anthony Bloom, Kevin W. Bowman, John R. Worden, Greet Janssens-Maenhout, and Robert J. Parker. 6/12/2019. “Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010–2015.” Atmospheric Chemistry and Physics, 19, 11, Pp. 7859-7881. Publisher's VersionAbstract
We use 2010–2015 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'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 2010–2015 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±0.4 years), indicating that satellite observations of atmospheric methane could provide a proxy for OH concentrations in the future.
Jianxiong Sheng, Shaojie Song, Yuzhong Zhang, Ronald G. Prinn, and Greet Janssens-Maenhout. 5/21/2019. “Bottom-Up Estimates of Coal Mine Methane Emissions in China: A Gridded Inventory, Emission Factors, and Trends.” Environmental Science and Technology Letters. Publisher's VersionAbstract
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° × 0.25°) methane emission inventory for China’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’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.
Yuzhong Zhang, Ritesh Gautam, Daniel Zavala-Araiza, Daniel J. Jacob, Ruixiong Zhang, Lei Zhu, Jian-Xiong Sheng, and Tia Scarpelli. 2/5/2019. “Satellite-observed changes in Mexico’s offshore gas flaring activitylinked to oil/gas regulations.” Geophysical Research Letters. Publisher's VersionAbstract
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 2005–2017 to quantify gas flaring activity in Mexico's offshore production cluster, which produces ~50–70% of the country's oil and is among the world's largest oil fields. We estimate annual flared‐gas‐volume ranging from 5.5–20×109m3 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.
Shaojie Song, Meng Gao, Weiqi Xu, Yele Sun, Douglas R. Worsnop, John T. Jayne, Yuzhong Zhang, Lei Zhu, Mei Li, Zhen Zhou, Chunlei Cheng, Yibing Lv, Ying Wang, Wei Peng, Xiaobin Xu, Nan Lin, Yuxuan Wang, Shuxiao Wang, J. William Munger, Daniel Jacob, and Michael B. McElroy. 2/1/2019. “Possible heterogeneous hydroxymethanesulfonate (HMS) chemistry in northern China winter haze and implications for rapid sulfate formation.” Atmospheric Chemistry and Physics, 19, Pp. 1357-1371. Publisher's VersionAbstract
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.
2018
J.-X. Sheng, D.J. Jacob, J.D. Maasakkers, Y. Zhang, and M.P. Sulprizio. 11/29/2018. “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.” Atmos. Meas. Tech., 11, Pp. 6379-6388. Publisher's VersionAbstract
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◦ × 0.3125◦ 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 (7×7 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.
Ye Cheng, Yuhang Wang, Yuzhong Zhang, James H Crawford, Glenn S Diskin, Andrew J Weinheimer, and Alan Fried. 7/2018. “Estimator of surface ozone using formaldehyde and carbon monoxide concentrations over the eastern United States in summer.” Journal of Geophysical Research: Atmospheres. Publisher's VersionAbstract
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.
Yuzhong Zhang, Yuhang Wang, James Crawford, Ye Cheng, and Jianfeng Li. 5/2018. “Improve Observation-based Ground-level Ozone Spatial Distribution by Compositing Satellite and Surface Observations: A Simulation Experiment.” Atmospheric Environment, 180, Pp. 226-233. Publisher's VersionAbstract

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.

Yuzhong Zhang, Daniel J. Jacob, Joannes D. Maasakkers, Melissa P. Sulprizio, Jian-Xiong Sheng, Ritesh Gautam, and John Worden. 2018. “Monitoring global OH concentrations using satellite observations of atmospheric methane.” Atmospheric Chemistry and Physics, 18, 21, Pp. 15959-15973. Publisher's VersionAbstract
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.
2017
Ye Cheng, Yuhang Wang, Yuzhong Zhang, Gao Chen, James H. Crawford, Mary M. Kleb, Glenn S. Diskin, and Andrew J. Weinheimer. 7/8/2017. “Large biogenic contribution to boundary layer O3-CO regression slope in summer.” Geophysical Research Letters, 40. Publisher's VersionAbstract
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.
Baolei Lyu, Yuzhong Zhang, and Yongtao Hu. 2017. “Improving PM2.5 Air Quality Model Forecasts in China Using a Bias-Correction Framework.” Atmosphere, 8, 8, Pp. 147. Publisher's VersionAbstract
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 2014–2016 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.
Yufei Zou, Yuhang Wang, Yuzhong Zhang, and Ja-Ho Koo. 2017. “Arctic sea ice, Eurasia snow, and extreme winter haze in China.” Science Advances, 3, 3, Pp. e1602751. Publisher's VersionAbstract
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.
Ruixiong Zhang, Yuhang Wang, Qiusheng He, Laiguo Chen, Yuzhong Zhang, Hang Qu, Charles Smeltzer, Jianfeng Li, Leonardo Alvarado, Mihalis Vrekoussis, and others. 2017. “Enhanced trans-Himalaya pollution transport to the Tibetan Plateau by cut-off low systems.” Atmospheric Chemistry and Physics, 17, 4, Pp. 3083–3095. Publisher's VersionAbstract
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 2–6 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.
Yuzhong Zhang, Haviland Forrister, Jiumeng Liu, Jack E Dibb, Bruce Anderson, Joshua P Schwarz, Anne E Perring, Jose L Jimenez, Pedro Campuzano-Jost, Yuhang Wang, and others. 2017. “Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere.” Nature Geoscience.Abstract

enhanced brown carbon at high altitudes

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.

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