Regional Anthropogenic Emissions Research Articles

Evaluation of WRF-Chem PM2.5 simulations in Thailand with different anthropogenic and biomass-burning emissions

Thailand experiences severe air quality issues, predominantly due to PM2.5 pollution that surpasses WHO guidelines. The main sources are attributed to energy production, industrial activities, vehicular emissions, agricultural burning, and transboundary transport of pollutants. Understanding the transport and transformation of these pollutants is necessary for addressing air quality issues. The Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) provides information about meteorology, chemical reactions, and transport of trace gases and aerosols. The accuracy of WRF-Chem simulations greatly depends on the choice of anthropogenic and biomass burning emissions inventories. This study provides a detailed evaluation of these inventories to model PM2.5 concentrations in Thailand during both haze and off-haze seasons in 2019. We evaluated WRF-Chem using four anthropogenic emission inventories—CAMS-GLOB-ANT, ECLIPSE, HTAP, and REAS—and four biomass burning emissions inventories—FINN1.5, FINN2.5 MOD, FINN2.5 MODVAR, and QFED—using data from ground-based air quality stations, MODIS AOD, and MOPITT CO satellite data. Our findings suggest CAMS-GLOB-ANT performs optimally for North Thailand, while HTAP and REAS are more effective in Eastern Thailand. For biomass burning, FINN1.5 shows superior performance. The study also highlights the challenge in capturing PM2.5 diurnal variability, particularly due to inaccuracies in simulating the planetary boundary layer height during nighttime in complex terrains. Moreover, our analysis exhibits moderate model performances during the off-haze season while using global and regional anthropogenic emissions in Thailand, emphasizing the need for improving anthropogenic inventories for reliable air quality prediction. For biomass burning emissions, updating emission factors to reflect Thailand's specific vegetation types is recommended to improve WRF-Chem's representation of PM2.5 levels.

Tropical tropospheric ozone and carbon monoxide distributions: characteristics, origins, and control factors, as seen by IAGOS and IASI

Abstract. The characteristics and seasonal variability in the tropical tropospheric distributions of ozone (O3) and carbon monoxide (CO) were analysed based on in situ measurements provided by the In-service Aircraft for a Global Observing System (IAGOS) programme since 1994 and 2002, respectively, combined with observations from the Infrared Atmospheric Sounding (IASI) instrument on board the MetOp-A satellite since 2008. The SOFT-IO (SOft attribution using FlexparT and carbon monoxide emission inventories for In-situ Observation database) model, which couples back trajectories with CO emission inventories, was used to explore the origins and sources of the tropical CO observed by IAGOS. The highest O3 and CO mixing ratios occur over western Africa in the lower troposphere (LT: surface to 750 hPa) during the fire season (75 ppb of O3 at 2.5 km and 850 ppb of CO at 0.3 km over Lagos in January), mainly due to anthropogenic (AN) emissions and a major contribution from fires. The secondary maxima are observed in Asia in the mid-troposphere (MT: 750–300 hPa) and upper troposphere (UT: 300–200 hPa) in April for O3 and in the LT in January for CO, with larger contributions from AN emissions. The lowest O3 and CO mixing ratios occur over Caracas. In the tropical LT, the majority of the location clusters are affected by local and regional AN emissions. The highest AN impact is found over Asia, Arabia and eastern Africa, and South America (>75 % of CO). Biomass burning (BB) emissions also originate from local or regional sources but with stronger seasonal dependence. The highest BB impact is found over southern tropical Africa (57 %–90 %), except in April, mostly due to local fires, but also from Northern Hemisphere Africa in January (45 %–73 %) and Southern Hemisphere South America in October (29 % over Windhoek). In the MT and UT, AN emissions are more important and dominate in the eastern part of the tropics (from the Middle East to Asia). BB contributions are more important than in the LT, especially from the African fires in January and July and from South East and equatorial Asia in April and October. The overall highest amount of CO is exported from Africa, with the main transport pathway from the dry-season African regions towards the wet-season ones. In contrast, the impact of the Asian emissions in the LT and MT is limited on a local or regional scale. The transport of polluted Asian air masses is important in the UT during the Asian summer monsoon and post-monsoon seasons, when convection is active.

Sources of Air Pollution Health Impacts and Co‐Benefits of Carbon Neutrality in Santiago, Chile

AbstractThe population of Santiago, Chile, experiences air pollution above global health guidelines that is attributable in part to large anthropogenic emissions. This is compounded by geographic features and meteorological conditions that are prone to pollution accumulation as well as secondary pollution production. In recent years, there have been improvements in air quality; however, the future of air pollution in Santiago remains unclear due to its growing population and increased vehicle use. Mitigation efforts can be supported by characterizing sources of air pollution and estimating how changes in emissions could affect air quality in future years. In this study, we conduct simulations using a chemical transport model (GEOS‐Chem) and perform adjoint calculations to characterize the relationship between health impacts associated with exposure to PM2.5, O3, and NO2 and anthropogenic emissions. We incorporate model updates in a new nested domain simulation over Central South America including local and regional anthropogenic emissions inventories for Chile. We estimate that 2,490 (1,360, 4,060) PM2.5‐ and O3‐related premature deaths and 5,350 (1,320, 11,330) NO2‐related new pediatric asthma cases were associated with pollution exposure in Santiago in 2015 and that a majority of these health impacts were attributable to anthropogenic emissions. We identify emissions from transportation, energy generation, and residential combustion as the leading contributors to these health impacts. Additionally, we estimate that Chile's commitment to attain carbon neutrality by 2050 could result in benefits in Santiago of 3,230 (1,240, 7,160) avoided deaths and 2,590 (640, 5,500) avoided pediatric asthma cases in 2050 compared to business‐as‐usual emissions.

Fine particle trace elements at a mountain site in southern China: Source identification, transport, and health risks

Trace elements in atmospheric particulate matter play a significant role in air quality, human health, and biogeochemical cycles. In this study, the trace elements (Ca, Al, K, Fe, Na, Mg, Zn, Pb, Mn, Ti, Cu, Cr, Sr, Ni) in PM2.5 samples collected at the summit of Mt. Lushan were analyzed to quantify their abundance, source, transport, and health risks. During the whole sampling period, the major trace elements was Ca, Al, and K. While the trace metals with the lowest concentrations were Sr, Ni, Rb, and Cd. The trace elements were influenced by air mass transport routes, exhibiting an increasing trend of crustal elements in the northwesterly airmass and anthropogenic elements (Zn, Mn, Cu, and Ni) in the easterly air masses. Construction dust, coal + biomass burning, vehicle emission, urban nitrate-rich + urban waste incineration emissions, and soil dust + industry emissions were common sources of PM2.5 on Mt. Lushan. Different air mass transport routes had various source contribution patterns. These results indicate that trace elements at Mt. Lushan are influenced by regional anthropogenic emissions and monsoon-dominated trace element transport. The total resulting cancer risk value that these elements posed were below the acceptable risk value of 1 × 10–6, while the non-carcinogenic risk value (1.72) was higher than the safety level, suggesting that non-carcinogenic effects due to these trace elements inhalation were likely to occur. Vehicle emission and coal + biomass burning were the common dominant sources of non-cancer risks posed by trace elements at Mt. Lushan.

Construction and Application of a Regional Kilometer-Scale Carbon Source and Sink Assimilation Inversion System (CCMVS-R)

CO2 is one of the most important greenhouse gases (GHGs) in the earth’s atmosphere. Since the industrial era, anthropogenic activities have emitted excessive quantities of GHGs into the atmosphere, resulting in climate warming since the 1950s and leading to an increased frequency of extreme weather and climate events. In 2020, China committed to striving for carbon neutrality by 2060. This commitment and China’s consequent actions will result in significant changes in global and regional anthropogenic carbon emissions and therefore require timely, comprehensive, and objective monitoring and verification support (MVS) systems. The MVS approach relies on the top-down assimilation and inversion of atmospheric CO2 concentrations, as recommended by the Intergovernmental Panel on Climate Change (IPCC) Inventory Guidelines in 2019. However, the regional high-resolution assimilation and inversion method is still in its initial stage of development. Here, we have constructed an inverse system for carbon sources and sinks at the kilometer level by coupling proper orthogonal decomposition (POD) with four-dimensional variational (4DVar) data assimilation based on the weather research and forecasting–greenhouse gas (WRF-GHG) model. Our China Carbon Monitoring and Verification Support at the Regional level (CCMVS-R) system can continuously assimilate information on atmospheric CO2 and other related information and realize the inversion of regional and local anthropogenic carbon emissions and natural terrestrial ecosystem carbon exchange. Atmospheric CO2 data were collected from six ground-based monitoring sites in Shanxi Province, China to verify the inversion effect of regional anthropogenic carbon emissions by setting ideal and real experiments using a two-layer nesting method (at 27 and 9 km). The uncertainty of the simulated atmospheric CO2 decreased significantly, with a root-mean-square error of CO2 concentration values between the ideal value and the simulated after assimilation was close to 0. The total anthropogenic carbon emissions in Shanxi Province in 2019 from the assimilated inversions were approximately 28.6% (17%–38%) higher than the mean of five emission inventories using the bottom-up method, showing that the top-down CCMVS-R system can obtain more comprehensive information on anthropogenic carbon emissions.

Changes in Atmospheric Gaseous Elemental Mercury Concentrations and Isotopic Compositions at Mt. Changbai During 2015–2021 and Mt. Ailao During 2017–2021 in China

AbstractChina is the largest contributor to the global total anthropogenic mercury (Hg) emissions. However, the trend in anthropogenic Hg emissions in recent years in China has not been effectively evaluated due to the lack of long‐term atmospheric Hg observations. This study documents the changes in atmospheric gaseous elemental mercury (GEM) concentrations and isotopic compositions at Mt. Changbai (MCB) in northeastern China during 2015–2021 and Mt. Ailao (MAL) in southwestern China during 2017–2021, and explores the potential factors controlling these changes. GEM concentrations showed continuous declines from 2015 to 2021 (−2.1 ± 0.6% yr−1) at MCB and from 2017 to 2021 (−4.0 ± 1.4% yr−1) at MAL. Accompanied with these GEM declines are positive shifts in δ202Hg (medians: from 0.42 to 0.46‰ at MCB and from 0.17 to 0.57‰ at MAL), and negative shifts in Δ199Hg (medians: from −0.17‰ to −0.21‰ at MCB and from −0.10‰ to −0.17‰ at MAL) and Δ200Hg values (medians: from −0.07‰ to −0.08‰ at MCB and from −0.03‰ to −0.05‰ at MAL) (at significant levels for Δ199Hg at MCB and δ202Hg and Δ199Hg at MAL). These changes were mainly caused by the decreases in regional anthropogenic emissions in the study areas. Based on a ternary mixing model with Δ199Hg and Δ200Hg as input, we estimate decline rates of 5.8 ± 2.8 and 4.8 ± 3.0% yr−1 for the regional anthropogenic GEM emissions in northeastern and southwestern China, respectively.

Simulation of Anthropogenic CO2 Emissions in the Yangtze River Delta Based on Different Emission Inventories

Nowadays, great uncertainty still exists on the urban- and regional-scale anthropogenic CO2 emission estimation based on emission inventories. In order to achieve the carbon peaking and neutrality targets for China, it is urgent to accurately estimate anthropogenic CO2 emissions at regional scales, especially in large urban agglomerations. Using two inventories (EDGAR v6.0 inventory and a modified inventory combining EDGAR v6.0 with GCG v1.0) as prior anthropogenic CO2 emission datasets andtaking themas input data respectively, this study utilized the WRF-STILT atmospheric transport model to simulate atmospheric CO2 concentration in the Yangtze River Delta region from December 2017 to February 2018. The simulated atmospheric CO2 concentrations were further improved by referencing atmospheric CO2 concentration observation at a tall tower in Quanjiao County of Anhui Province and using the scaling factors obtained from the Bayesian inversion method. An estimation of anthropogenic CO2 emission flux in the Yangtze River Delta regionwas finally accomplished. The results indicated that:①in winter, in comparison to the atmospheric CO2 concentration simulated based on EDGAR v6.0, the atmospheric CO2 concentration simulated based on the modified inventory was more consistent with observed values. ②The simulated atmospheric CO2 concentration was higher than observation at night and lower than observation during the daytime. The CO2 emission data of emission inventories could not fully reflect the diurnal variation in anthropogenic emissions, andtheoverestimation, caused by the simulated low-atmospheric boundary layer height at night, of the contribution from point sources with higher emission height near the observation station were the main reasons. ③The simulation performance on atmospheric CO2 concentration was greatly affected by the emission bias of the EDGAR grid points that significantly contributed to concentrations of the observation station, and this indicated that the uncertainty in the spatial distribution in EDGAR emission was the main factor influencing the simulation accuracy. ④The posterior anthropogenic CO2 emission flux in the Yangtze River Delta from December 2017 to February 2018 was around (0.184±0.006) mg·(m2·s)-1and (0.183±0.007) mg·(m2·s)-1 based on EDGAR and the modified inventory, respectively. It is suggested that the inventories with higher temporal and spatial resolutions and more accurate spatial emission distribution should be selected as the prior emissions to obtain a more accurate estimation of the regional anthropogenic CO2 emissions.

Characteristics of Surface Ozone and Nitrogen Oxides over a Typical City in the Yangtze River Delta, China

The Yangtze River Delta (YRD) is the most developed region in China. Influenced by intensive and complex anthropogenic activities, atmospheric pollution in this region is highly variable, and reports are sparse. In this study, a seven-year history of the atmospheric O3 and NOx mixing ratios over a typical city, Hangzhou, was presented to enrich the studies on air pollution in the YRD region. Our results revealed that the diurnal variation in NOx corresponded to traffic rush hours, while O3 was mainly impacted by photochemical reactions in the daytime. The weekend effect was significant for NOx, but inapparent for O3. Two O3 peaks in May and September were caused by seasonal atmospheric stability and climatic conditions. The lower NOx and higher O3 levels observed suggested direct effects from traffic restrictions and large-scale industrial shutdowns during the COVID-19 lockdown in 2020 compared with those in the periods before and after lockdown. The model simulation results showed that O3 mixing ratios were not only related to regional anthropogenic emissions but were impacted by air mass transportation from surrounding provinces and the China shelf seas. The NOx mixing ratios showed a decreasing trend, while the O3 mixing ratios showed the opposite trend from 2015 to 2021, which is indicative of the implementation of the Air Pollution Prevention and Control Acton Plan issued by the Chinese government in 2013.

Pollution and transport of atmospheric PAHs in Xinjiang: Observation at a high-altitude background site combined with numerical simulation

As an essential energy production base in China, the pollution of PAHs in Xinjiang cannot be ignored. However, this region has limited studies on the overall distribution and transport characteristics of polycyclic aromatic hydrocarbons (PAHs). This study used a combination of high-altitude background site (MTtian) observations and Community Multiscale Air Quality simulations for systematic investigation. The simulation results revealed that the distribution of PAHs in Xinjiang was high in the north and low in the south, primarily associated with emissions. Moreover, the observed concentration of PAHs in the MTtian was 1.37 ng/m3, which lies between the clean and polluted background sites, emphasizing the importance of regional anthropogenic emissions. The observed PAH concentrations at MTtian was 32.2% higher when the air mass was from Urumqi than those at other places. This is related to mountain-valley winds, as shown by the simulations. In addition, the transport of high-altitude PAHs in Xinjiang is primarily affected by westerly winds. This mechanism can explain the highly simulated PAHs at high altitudes in the Tarim Basin. The PAHs emitted from Xinjiang were transported eastward downstream, with Mongolia being the most affected region, contributing to 7.33% of the total PAHs.

The first high resolution PAH record of industrialization over the past 200 years in Liaodong Bay, northeastern China

Polycyclic aromatic hydrocarbons (PAHs) are excellent tracers for fossil fuel combustion, natural fires and petroleum contamination, and have been widely used for reconstructing past wildfires and industrial activities at a variety of time scales. Here, for the first time, we obtain a high resolution (annual to decadal scale) record of PAHs from two parallel marine sediment cores from the Liaodong Bay, Northeastern China to reconstruct the industrial activities, spanning the past ∼ 200 years from 1815 to 2014. Our data indicate that PAH variations can be divided into four episodes: I) low (probably near background) PAHs from natural fires and domestic wood combustion during the pre-industrial period from 1815 to 1890; II) slightly increased (but with large fluctuations) PAH concentrations derived from intermittent warfare during the World War (1891–1945) and increased industrial activities after 1946 (1946–1965); III) a period of stagnation and, in some cases, reduction in PAHs during the “Cultural Revolution” (1966 to 1979); and IV) a rapid and persistent rise in PAHs post 1979 linked to fast economic development, with PAH concentrations doubled from 1979 to 2014. Changes in PAH distributions demonstrate major shifts in the dominant types of fuels over time from vegetation/wood, to coal and wood, followed by coal and petroleum (including vehicle emissions) over the past 200 years. We find that PAH records also show similar trend to domestic economy and the estimated regional Anthropocene CO2 emissions from industrial activities, suggesting sedimentary PAH fluxes could be used as an indirect and qualitative proxy to track the trend for regional anthropogenic CO2 emissions.

Anthropogenic impact on arctic near-surface methane: observations and model simulations

Impact of climatically significant anthropogenic emissions to seasonal methane (CH4) variations observed at arctic and subarctic background stations in 1999 – 2019 has been quantitatively estimated using GEOS-Chem chemical transport model. It is shown that the formation of a stable continental pollution plume from sources in Western Europe, European Russia and Siberia allows to explain up to 5.5–8.6 % of observed CH4 surface concentration (~104–165 ppb). These atmospheric response values are several times higher than the of the observed annual methane variability amplitude (22–36 ppb), which allows to conclude that regional anthropogenic methane emissions sources play a significant role in regional CH4 balance in arctic and subarctic areas.

The UrbEm Hybrid Method to Derive High-Resolution Emissions for City-Scale Air Quality Modeling

As cities are growing in size and complexity, the estimation of air pollution exposure requires a detailed spatial representation of air pollution levels, rather than homogenous fields, provided by global- or regional-scale models. A critical input for city-scale modeling is a timely and spatially resolved emission inventory. Bottom–up approaches to create urban-scale emission inventories can be a demanding and time-consuming task, whereas local emission rates derived from a top–down approach may lack accuracy. In the frame of this study, the UrbEm approach of downscaling gridded emission inventories is developed, investing upon existing, open access, and credible emission data sources. As a proof-of-concept, the regional anthropogenic emissions by Copernicus Atmospheric Monitoring Service (CAMS) are handled with a top–down approach, creating an added-value product of anthropogenic emissions of trace gases and particulate matter for any city (or area) of Europe, at the desired spatial resolution down to 1 km. The disaggregation is based on contemporary proxies for the European area (e.g., Global Human Settlement population data, Urban Atlas 2012, Corine, OpenStreetMap data). The UrbEm approach is realized as a fully automated software tool to produce a detailed mapping of industrial (point), (road-) transport (line), and residential/agricultural/other (area) emission sources. Line sources are of particular value for air quality studies at the urban scale, as they enable explicit treatment of line sources by models capturing among others the street canyon effect and offer an overall better representation of the critical road transport sector. The UrbEm approach is an efficient solution for such studies and constitutes a fully credible option in case high-resolution emission inventories do not exist for a city (or area) of interest. The validity of UrbEm is examined through the evaluation of high-resolution air pollution predictions over Athens and Hamburg against in situ measurements. In addition to a better spatial representation of emission sources and especially hotspots, the air quality modeling results show that UrbEm outputs, when compared to a uniform spatial disaggregation, have an impact on NO2 predictions up to 70% for urban regions with complex topographies, which corresponds to a big improvement of model accuracy (FAC2 > 0.5), especially at the source-impacted sites.

Spatiotemporal Characterization of Mercury Isotope Baselines and Anthropogenic Influences in Lake Sediment Cores

AbstractIncreasing mercury isotope ratios from pre‐industrial (1510–1850) to present‐day (1990–2014) in lake sediment cores have been suggested to be a global phenomenon. To assess factors leading to spatiotemporal changes, we compiled mercury concentration (THg) and mercury isotope ratios in 22 lake sediment cores located at various regions of the world. We find that the positive δ202Hg shifts together with THg increases from pre‐industrial to present‐day are a widespread phenomenon. This is caused by increased contribution of mercury from local to regional anthropogenic mercury emission sources, which lead to higher sediment δ202Hg (−1.07 ± 0.69‰, 1 SD) than pre‐industrial sediments (−1.55 ± 0.96‰, 1 SD). The positive Δ199Hg shifts were observed in 15 lake sediment cores, which have low pre‐industrial Δ199Hg (−0.20 ± 0.32‰) compared to the sediment cores with near‐zero to positive pre‐industrial Δ199Hg (0.08 ± 0.07‰). The magnitudes of δ202Hg (r2 = 0.09) and Δ199Hg (r2 = 0.20, both p > 0.05) changes from pre‐industrial to present‐day did not correlate with the magnitude of THg changes. Instead, the magnitudes of δ202Hg and Δ199Hg changes decreased with increasing pre‐industrial δ202Hg and Δ199Hg values, suggesting that the baseline mercury isotope ratios play a more important role in determining the magnitude of mercury isotope changes compared to the degree of THg input. We suggest that the spatiotemporal assessments of δ202Hg in lake sediment cores can be used as an important proxy for monitoring changes in anthropogenic mercury sources for the Minamata Convention on Mercury.

On the Emergence of Human Influence on Surface Air Temperature Changes Over India

AbstractHuman activities in terms of greenhouse gas (GHG) emissions and aerosols resulting from the combustion of fossil fuels have been shown to have affected the temperature of the Earth on global and continental scales. The surface air temperature (TAS) over India has also been observed to be increasing over the last 100 years. Understanding the underlying causes of regional climate change over India can help in developing appropriate mitigation and adaptation strategies. Differentiating signals of externally forced climate changes from the noise of natural internal variability generally becomes more difficult as spatial scale reduces. Therefore detecting and attributing the influence of external forcings such as GHGs and aerosols is harder at local and regional scales. In this study, we applied a detection and attribution (D&A) method to study annual and seasonal mean TAS over the Indian region. We found that the observed warming over India from 1906 to 2005 cannot be explained by natural climate variability alone. We found that the warming is largely driven by the increase in GHGs, and partially offset by regional anthropogenic emissions of aerosols. These results were confirmed for the shorter 1956–2005 period, but results were sensitive to the choice of observational data set. The changes cannot be explained by internal climate variability or natural external forcings alone, but are compatible with the responses to combined anthropogenic GHG and aerosol forcings.

Regional Impact of Ozone Precursor Emissions on NOX and O3 Levels at ZOTTO Tall Tower in Central Siberia

AbstractSeasonal variations of the near‐surface NOX (= NO + NO2) and ozone (O3) mixing ratios at Zotino Tall Tower (ZOTTO), a remote site in central Siberia, are described for years 2007–2014. Conditional probability function analysis and back trajectories are used to determine the origins of clean (continental baseline, CB) and regional emissions‐influenced air. High NOX levels at the site are observed for air from industrial regions of western Siberia and Ural Mountains, whereas CB air originates from remote areas of North Eurasia within 55°–70°N. The estimated annual means of daytime O3 and NOX mixing ratios for CB air are 27.0 and 0.44 ppbv, correspondingly, versus the similar quantities of 27.9 and 0.79 ppbv for all data. Monthly ozone for CB air shows a distinct maximum in April, as is the case for Northern Hemisphere midlatitude baseline (NHMLB) air at the European inflow boundary according to the surface ozone data for Mace Head and Norwegian monitoring sites, and a minimum in late summer–early autumn reflecting a weak continental‐scale ozone production from biogenic sources of ozone precursors and wildfire emissions throughout the warm season. During spring and early summer under hot weather conditions, regional anthropogenic and wildfire emissions are an important source for ozone in the continental boundary layer over southern and central Siberia, resulting in surface ozone levels compared to or larger than those observed in NHMLB air. Throughout the remaining part of year, the central North Eurasia represents a sink for tropospheric ozone on a hemispheric scale.

Multidimensional Verification of Anthropogenic VOCs Emissions Inventory Through Satellite Retrievals and Ground Observations

In this paper, a regional emissions inventory of anthropogenic VOCs was established based on the traditional emissions factor method for the Beijing-Tianjin-Hebei (BTH) region, followed by a multidimensional calibration study based on regional satellite remote sensing information for formaldehyde and typical urban ground VOCs. Inventory calculations showed that the VOCs emissions in BTH in 2013, 2015, and 2017 were 2026700, 2073400, and 1934200 tons, respectively, comprising alkanes (29.83% to 30.72%), unsaturated hydrocarbons (16.54% to 17.68%), aromatic hydrocarbons (27.14% to 27.51%), aldehydes (8.75% to 9.52%), ketones (8.13% to 9.04%), and aldehydes and ketones lipids (5.13% to 6.60%). During 2013-2017, the emission of VOCs in Zhangjiakou, Qinhuangdao, and Hengshui increased slightly (1.10% to 1.66% per year); emissions in Xingtai and Handan decreased slightly (-1.46% to -1.12% per year); and emissions in Chengde, Tangshan, Baoding, and Cangzhou were stable. There trends were consistent with the inter-annual trend of satellite-derived HCHO column concentrations. However, in Beijing, Tianjin, Langfang, and Shijiazhuang, annual variations in VOCs emissions (-6.51%, -3.30%, 2.16%, and 0.11% per year) and HCHO column concentrations (-1.17%, 7.19%, -0.24%, and 6.68% per year) were observed, respectively. In the regional VOCs inventory, a good linear correlation (R>0.5) was achieved between the grid emissions of VOCs and HCHO column concentrations in urban areas, while the correlation was only 0.33 in suburban areas. This is mainly due to the important influence of secondary conversion of VOCs originating from natural sources to HCHO in suburban areas. In addition, ground-level VOCs concentrations were observed in the urban areas of Beijing and Handan, where the emission ratios (ERs) of VOCs and CO were regressed. The ERs of most hydrocarbons were in good agreement with the regressed ERs, but the ERs of ethane were significantly lower (-156% to -73%) and the ERs of aromatic hydrocarbons above C8 were relatively high (54% to 74%). In general, the regional anthropogenic VOCs emissions inventory established in this paper offers high accuracy and reliability.

Impact of regional Northern Hemisphere mid-latitude anthropogenic sulfur dioxide emissions on local and remote tropospheric oxidants

Abstract. The unintended consequences of reductions in regional anthropogenic sulfur dioxide (SO2) emissions implemented to protect human health are poorly understood. SO2 decreases began in the 1970s in the US and Europe and are expected to continue into the future, while recent emissions decreases in China are also projected to continue. In addition to the well-documented climate effects (warming) from reducing aerosols, tropospheric oxidation is impacted via aerosol modification of photolysis rates and radical sinks. Impacts on the hydroxyl radical and other trace constituents directly affect climate and air quality metrics such as surface ozone levels. We use the Geophysical Fluid Dynamics Laboratory Atmospheric Model version 3 nudged towards National Centers for Environmental Prediction (NCEP) reanalysis wind velocities to estimate the impact of SO2 emissions from the US, Europe, and China by differencing a control simulation with an otherwise identical simulation in which 2015 anthropogenic SO2 emissions are set to zero over one of the regions. Springtime sulfate aerosol changes occur both locally to the emission region and also throughout the Northern Hemispheric troposphere, including remote oceanic regions and the Arctic. Hydroperoxy (HO2) radicals are directly removed via heterogeneous chemistry on aerosol surfaces, including sulfate, in the model, and we find that sulfate aerosol produced by SO2 emissions from the three individual northern mid-latitude regions strongly reduces both HO2 and hydroxyl (OH) by up to 10 % year-round throughout most of the troposphere north of 30∘ N latitude. Regional SO2 emissions significantly increase nitrogen oxides (NOx) by about 5 %–8 % throughout most of the free troposphere in the Northern Hemisphere by increasing the NOx lifetime as the heterogeneous sink of HO2 on sulfate aerosol declines. Despite the NOx increases, tropospheric ozone decreases at northern mid-latitudes by 1 %–4 % zonally averaged and by up to 5 ppbv in summertime surface air over China, where the decreases in HO2 and OH suppress O3 production. Since 2015 anthropogenic SO2 emissions in China exceed those in the US or Europe, the oxidative response is greatest for the China perturbation simulation. Chemical effects of aerosols on oxidation (reactive uptake) dominate over radiative effects (photolysis rates), the latter of which are only statistically significant locally for the large perturbation over China. We find that the SO2 emissions decrease in China, which has yet to be fully realized, will have the largest impact on oxidants and related species in the Northern Hemisphere free troposphere compared to future decreases in Europe or the US. Our results bolster previous calls for a multipollutant strategy for air pollution mitigation to avoid the unintended consequence of aerosol removal leading to surface ozone increases that offset or mask surface ozone gains achieved by regulation of other pollutants, especially in countries where current usage of high-sulfur emitting fuels may be phased out in the future.

Identification of potential sources of elevated PM2.5-Hg using mercury isotopes during haze events

Atmospheric mercury (Hg) pollution has become a serious problem in megacities. In this study, we applied Hg isotopes together with backward-trajectory receptor models to investigate the potential sources and transport of elevated PM2.5-Hg during two haze events in autumn (Oct. and Nov. in 2014) and winter (Jan. in 2015). Results showed that the sources and transport patterns of PM2.5-Hg during haze are complex for different seasons. In autumn, the dominant sources were local and/or regional anthropogenic emissions from northern China, whereas the long-range transport contribution of biomass burning originated from northeastern China in 2014 and eastern China in 2015. Notably, the biomass burning from northeastern China served as an important contribution to elevated PM2.5-Hg in winter. Our data set also suggested that the Δ200HgPBM values may be due to heterogeneous photoreactions on the particles emitted by coal burning, smelting, and cement production, along with photooxidation from the upper troposphere, and could be used as a potential indicator of particle-bound mercury sources owing to its contribution to the exhibited variability. Hg isotopes, together with meteorological models, could be employed to trace the sources of particle-bound Hg in the atmosphere. This study provides a new way to explore the potential sources of atmospheric particulate mercury and its vectors during haze evolution.

Quantifying the impacts of anthropogenic and natural perturbations on gaseous elemental mercury (GEM) at a suburban site in eastern China using generalized additive models

Long-term observation of atmospheric mercury (Hg) concentration and observation-based statistical methods are important tools to quantify the impacts of anthropogenic and natural perturbation on the global atmospheric Hg reservoir. In this study, two campaigns were conducted at a suburban site in eastern China with continuous measurements of gaseous elemental mercury (GEM) during the periods of August 2014 to July 2015 (Campaign 1) and May 2018 to April 2019 (Campaign 2). The overall mean GEM concentrations were 3.77 ± 1.32 and 3.24 ± 1.26 ng m−3, respectively. The potential source contribution function (PSCF) model based on backward trajectories were used to examine the variation of the potential source regions for GEM in different seasons. Generalized additive models (GAMs) were utilized in this study to quantify the impacts of local anthropogenic emissions, regional transport, and meteorological factors on the GEM concentration. Case studies with results from GAMs and observations of other air pollutants were conducted to provide more evidence for impacting mechanisms. The reduction of model residuals and the variation of contributions from direction and distance of air parcel transport imply the alleviation of local and regional anthropogenic Hg emissions from Campaign 1 to Campaign 2, respectively. The impact of relative humidity on GEM was crucial via the reduction of Hg(II) in droplets or on particles in the atmosphere. The impact of air stagnation on GEM was embodied mainly through the contribution of wind speed and partially by day of year (DOY) in winter. One DOY-controlled case also indicates the impacts of the 2015 El Niño event. With the decrease of anthropogenic emissions, the impacts of meteorological factors on GEM are getting more and more prominent. GAMs provide a promising tool for better understanding how anthropogenic and natural perturbations affect atmospheric Hg pollution.

SNOW ALBEDO REDUCTION IN CENTRAL ANDES BY ATMOSPHERIC AEROSOLS: CASE STUDY ON THE TUNUYÁN BASIN (ARGENTINA)

Abstract. Changes in snow albedo (SA) on several basins of the central Andes of Argentina are associated with the possible deposition of light-absorbing particles (LAP) in the austral spring. To demonstrate this possibility, we correlate SA with daily data of snow cover (SC), aerosol optical depth (AOD) and land surface temperature (LST) available from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on board NASA Terra satellite during 2000–2016, and other derived parameters such as days after albedo (DAS) and snow precipitation (SP) from the Tropical Rainfall Measuring Mission (TRMM). We used satellite pixels with 100% snow cover to obtain monthly average value of SA, LST, AOD, DAS and SP performing multiple regression analysis. Further, we analysed biomass burning emissions in northern Argentina using MODIS products MCD64 collection C6 as possible source for snow pollution. Aerosol deposition and trajectories were analysed using WRF-Chem atmospheric numerical prediction model, with inventories of regional anthropogenic emissions of own elaboration (lat. 0.025° × long. 0.025°) and the estimation of open burning emissions from the FINN global inventory (Fire INventory from NCAR).