Regional Anthropogenic Emissions Research Articles

Chemical characterization and source apportionment of fine and coarse atmospheric particulate matter in Doha, Qatar

Atmospheric particulate matter of two size fractions (i.e., PM2.5 and PM10) were sampled simultaneously at an urban site in Doha, Qatar, and characterized to measure chemical constituents (including trace elements, organic and elemental carbon (OC/EC), and water-soluble ions). The composition data were applied to mass closure analysis and Positive Matrix Factorization (PMF) model along with detailed wind direction analysis for quantifying and identifying the probable sources of both PM size fractions. The average concentrations of PM2.5 (40 μg m−3) and PM10 (146 μg m−3) were greatly exceeded the WHO air quality thresholds for 78–92% of the sampling days. Mass closure indicated the predominance of secondary inorganic aerosol (39%) and EC (7%) in fine PM, while mineral dust contributes 50% to the total mass of coarse particles. PMF identified six major sources of fine and coarse PM, including secondary inorganic aerosols, vehicular emissions, heavy oil combustion, marine aerosols, mineral and fugitive dust. The wind direction analysis indicated that both local and regional sources impact Qatar's air quality attributed to specific wind conditions. Two main sources of heavy oil combustion and secondary aerosols are closely related to regional emissions from shipping vessels and the petrochemical industry in the Gulf region. The desert dust transport mixed with local re-suspended dust and sea-salt particles also contributes considerably to the local PM concentrations. The significant contributions of regional anthropogenic and natural emissions pose a significant challenge in meeting local PM standards, signifying the importance of regional collaboration for better control policies on reducing transboundary air pollution.

Meteorology-normalized impact of the COVID-19 lockdown upon NO<sub>2</sub> pollution in Spain

Abstract. The spread of the new coronavirus SARS-CoV-2 that causes COVID-19 forced the Spanish Government to implement extensive lockdown measures to reduce the number of hospital admissions, starting on 14 March 2020. Over the following days and weeks, strong reductions in nitrogen dioxide (NO2) pollution were reported in many regions of Spain. A substantial part of these reductions was obviously due to decreased local and regional anthropogenic emissions. Yet, the confounding effect of meteorological variability hinders a reliable quantification of the lockdown's impact upon the observed pollution levels. Our study uses machine-learning (ML) models fed by meteorological data along with other time features to estimate the “business-as-usual” NO2 mixing ratios that would have been observed in the absence of the lockdown. We then quantify the so-called meteorology-normalized NO2 reductions induced by the lockdown measures by comparing the estimated business-as-usual values with the observed NO2 mixing ratios. We applied this analysis for a selection of urban background and traffic stations covering the more than 50 Spanish provinces and islands. The ML predictive models were found to perform remarkably well in most locations, with an overall bias, root mean square error and correlation of +4 %, 29 % and 0.86, respectively. During the period of study, from the enforcement of the state of alarm in Spain on 14 March to 23 April, we found the lockdown measures to be responsible for a 50 % reduction in NO2 levels on average over all provinces and islands. The lockdown in Spain has gone through several phases with different levels of severity with respect to mobility restrictions. As expected, the meteorology-normalized change in NO2 was found to be stronger during phase II (the most stringent phase) and phase III of the lockdown than during phase I. In the largest agglomerations, where both urban background and traffic stations were available, a stronger meteorology-normalized NO2 change is highlighted at traffic stations compared with urban background sites. Our results are consistent with foreseen (although still uncertain) changes in anthropogenic emissions induced by the lockdown. We also show the importance of taking the meteorological variability into account for accurately assessing the impact of the lockdown on NO2 levels, in particular at fine spatial and temporal scales. Meteorology-normalized estimates such as those presented here are crucial to reliably quantify the health implications of the lockdown due to reduced air pollution.

Yearlong first measurements of black carbon in the western Indian Himalaya: Influences of meteorology and fire emissions

Measurements of equivalent black carbon (EBC) aerosols are presented for the first time from a high-altitude station Ranichauri (30°18′ N, 78°24′ E; 2200 m amsl) in the lesser Himalaya during January-December 2016. The influences of meteorology, fire emissions and transport, on [EBC] variations have been investigated here. The daily mean values of [EBC] are observed to vary from 0.04 ± 0.03 μgm−3 to 7.83 ± 2.66 μgm−3 with peak during April. A significant enhancement in [EBC] is observed towards the end of April, reaching the levels as high as 23.95 μgm−3 and attributed to fire emissions. Diurnal variations are suppressed with typically lower [EBC] levels during the summer monsoon (0.42 ± 0.25 μg m−3 in July) due to the transport of marine air mass and scavenging. On a seasonal basis, the average [EBC] levels are found to be higher during winter (2.72 ± 1.86 μgm−3) and pre-monsoon (2.56 ± 1.80 μg m−3), and lowest during the summer monsoon (0.89 ± 01.03 μg m−3).Our measurements in conjunction with the analysis of model meteorology (Era Interim reanalysis) show profound effects of boundary layer dynamics on EBC concentrations. Wintertime [EBC] maximum is suggested to be due to confinement of regional anthropogenic emissions in shallow boundary layer. In addition, transport from the North-West, and Western regions, characterized by wood-burning and fossil fuel combustion, also affected [EBC] the variations here, except during the summer monsoon.

Sources, frequency, and chemical nature of dust events impacting the United States East Coast.

This study examines 14 years (2004-2017) of surface aerosol composition data from the EPA IMPROVE network with a focus on the monthly profile, sources, and chemical nature of extreme dust events (>92nd percentile of fine soil concentration each month) impacting ten sites along the United States East Coast ranging in latitude from Florida to Maine. Based on trajectory, remote sensing, and reanalysis data, dust events were categorized into four source categories: African, Asian, Mix (African + Asian), and Other (anything other than African and Asian). The results reveal that extreme dust events account for between 3.3% and 4.6% of total available days depending on the site. March-April-May (MAM) had the most (174) dust events, followed by June-July-August (JJA) with 172, and then by September-October-November (SON) with 160 and December-January-February (DFJ) with 150. There is a variability in the predominant dust sources based on latitude, with African and Other sources more influential from North Carolina to the south, while Asian and Other were most important from New Jersey to the north. The Mix category is consistently the least frequent dust category at all sites. The African dust category was linked to the highest fine soil levels across the entire East Coast relative to other sources regardless of location. JJA is mostly impacted by African dust for sites ranging from Florida to New Jersey, while MAM is dominated by Asian dust for all sites. Mix events occurred mostly between April and October and Other events were most common outside of MAM and JJA seasons. Seven out of ten sites had Other as the most dominant source. Aerosol constituents organic carbon (OC) and elemental carbon (EC) had higher average concentrations in Other events (2.39 ± 0.78 μg m-3 and 0.79 ± 0.81 μg m-3, respectively) as compared to the other three source categories, suggestive of regional anthropogenic emissions. Moreover, the ratios of elements (Si:Al, K:Fe, Fe:Ca, Al:Ca) contributing to fine soil and PM2.5:PM10 exhibited distinct values depending on the dust source category and the site. This study builds on the growing evidence of the importance of long-range transport of dust in impacting distant regions and how a variety of sources can impact the U.S. East Coast at all times of the year.

Regional haze formation enhanced the atmospheric pollution levels in the Yangtze River Delta region, China: Implications for anthropogenic sources and secondary aerosol formation

High-time-resolution (3-hour) PM2.5 samples were collected simultaneously from the rural and urban areas in the Yangtze River Delta region during winter. The aerosol samples were analyzed for carbonaceous components, organic tracers, water-soluble inorganic ions and stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions of total carbon and total nitrogen. The values of PM2.5 and secondary organic carbon (SOC) for both sampling sites were observed 2 times higher in haze events compare to those in clear days, implying severe pollution occurred by photochemical oxidation during haze periods. The PM mass of rural samples showed similar temporal trend and significant correlation with the urban PM, reflecting pollution sources or their formation process are most likely identical. Diurnal variations of PM2.5 and carbonaceous components revealed that pollution levels increased at daytime due to the photochemical oxidation. In addition, SOC and OC were influenced by the relative humidity (RH%) and temperature (T °C), indicating that such meteorological factors play important roles in the occurrence of regional air pollution. The concentrations of levoglucosan, polycyclic aromatic hydrocarbons, hopanes, and n-alkanes were 625 ± 456 and 519 ± 301 ng m−3, 32.6 ± 24.7 and 28.7 ± 20.1 ng m−3, 1.83 ± 1.51 and 1.26 ± 1.34 ng m−3, and 302 ± 206 and 169 ± 131 ng m−3 for rural and urban samples, respectively. Levoglucosan is the most abundant organic compounds, exhibited 2–3 times higher in haze than clear days, suggesting biomass burning (BB) emission substantially affects the haze pollution in winter. Furthermore, NO3− was the dominant ionic species followed by SO42−, NH4+, Cl− and other minor species for both sites. The δ13C and δ15N values demonstrate that anthropogenic activities such as fossil fuel combustion and BB are the major sources for carbonaceous and nitrogenous aerosols. This study implies that both the regional anthropogenic emissions and meteorological conditions influenced the regional haze formation, leading enhancement of pollution levels in eastern China during winter.

Estimates of Regional Source Contributions to the Asian Tropopause Aerosol Layer Using a Chemical Transport Model

AbstractThe Asian Tropopause Aerosol Layer (ATAL) represents an accumulation of aerosol in the upper troposphere and lower stratosphere associated with the Asian Summer Monsoon. Here we simulate the ATAL for summer 2013 with the GEOS‐Chem chemical transport model and explore the likely composition of ATAL aerosols and the relative contributions of regional anthropogenic sources versus those from farther afield. The model indicates significant contributions from organic aerosol, nitrate, sulfate, and ammonium aerosol, with regional anthropogenic precursor sources dominant. The model underestimates aerosol backscatter in the ATAL during summer 2013, compared with Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite instrument. Tests of a more physically based treatment of wet scavenging of SO2 in convective updrafts raise sulfate, eliminating the low bias with respect to CALIPSO backscatter in the ATAL, but lead to an unacceptable high bias of sulfate compared with in situ observations from aircraft over the United States. Source apportionment of the model results indicate the dominance of regional anthropogenic emissions from China and the Indian subcontinent to aerosol concentrations in the ATAL; ~60% of sulfate in the ATAL region in August 2013 is attributable to anthropogenic sources of SO2 from China (~30%) and from the Indian subcontinent (~30%), twice as much as in previously published estimates. Nitrate aerosol is found to be a dominant component of aerosol composition on the southern flank of the Asian Summer Monsoon anticyclone. Lightning sources of NOx are found to make a significant (10–15%) contribution to nitrate in the ATAL for the case studied.

A Clean Air Plan for Sydney: An Overview of the Special Issue on Air Quality in New South Wales

This paper presents a summary of the key findings of the special issue of Atmosphere on Air Quality in New South Wales and discusses the implications of the work for policy makers and individuals. This special edition presents new air quality research in Australia undertaken by (or in association with) the Clean Air and Urban Landscapes hub, which is funded by the National Environmental Science Program on behalf of the Australian Government’s Department of the Environment and Energy. Air pollution in Australian cities is generally low, with typical concentrations of key pollutants at much lower levels than experienced in comparable cities in many other parts of the world. Australian cities do experience occasional exceedances in ozone and PM2.5 (above air pollution guidelines), as well as extreme pollution events, often as a result of bushfires, dust storms, or heatwaves. Even in the absence of extreme events, natural emissions play a significant role in influencing the Australian urban environment, due to the remoteness from large regional anthropogenic emission sources. By studying air quality in Australia, we can gain a greater understanding of the underlying atmospheric chemistry and health risks in less polluted atmospheric environments, and the health benefits of continued reduction in air pollution. These conditions may be representative of future air quality scenarios for parts of the Northern Hemisphere, as legislation and cleaner technologies reduce anthropogenic air pollution in European, American, and Asian cities. However, in many instances, current legislation regarding emissions in Australia is significantly more lax than in other developed countries, making Australia vulnerable to worsening air pollution in association with future population growth. The need to avoid complacency is highlighted by recent epidemiological research, reporting associations between air pollution and adverse health outcomes even at air pollutant concentrations that are lower than Australia’s national air quality standards. Improving air quality is expected to improve health outcomes at any pollution level, with specific benefits projected for reductions in long-term exposure to average PM2.5 concentrations.

Primary Suppliers Driving Atmospheric Mercury Emissions through Global Supply Chains

Summary The Minamata Convention on Mercury, which came into force in 2017, aims to control mercury-related risks to human beings and ecosystems by reducing anthropogenic mercury (Hg) emissions. Existing studies have identified direct atmospheric Hg emitters and final consumers causing atmospheric Hg emissions but overlooked primary suppliers driving atmospheric Hg emissions through global supply chains. Here, we identify critical primary suppliers and supply-chain paths for global atmospheric Hg emissions in 2015. Results show that China, Indonesia, and India are major primary suppliers causing global atmospheric Hg emissions. Major sectors and critical supply-chain paths from the supply viewpoint are related to resource extraction and power generation. Findings of this study can support supply-side measures to implement the Minamata Convention on Mercury, such as the optimization of labor and capital input structures and the optimization of product-allocation behaviors to downstream producers.

NOx-limiting regime of ozone generation in a weakly polluted boundary layer over Central Siberia as derived from O3 and Nox observations at Zotto tall tower observatory in 2007-2015

Quantitative estimates on the ozone production efficiency (OPE) per a molecular of NOx (=NO+NO2), ΔP, and ozone production rate, PQ, are derived for the region of Central Siberia based on near surface observations of O3, NO, and NO2) at Zotino Tall Tower Observatory in 2007-2015. Experimental data follow are a power law dependencies on NOx abundance: PQ χ [NOx]-n+1, ΔP χ [NOx]-n, n = 0,82±0,06 (coefficient of determination R2 = 0,66), with the power law exponent corresponding to a NOx-limiting regime of ozone production in a weakly polluted air mass. During summer, the value of ΔP ranges from 30,0-43,7 [mol.O3/mol.NOx] which agrees well with the corresponding estimate of 39,8 [mol.O3/mol.NOx] derived from GEOS‑chem CTM model simulations. The derived estimates provide an observation based conclusion on the important role of regional anthropogenic emissions of NOx in summertime ozone photochemistry in the remote areas of Siberia.

Evolution of sectoral emissions and contributions to mortality from particulate matter exposure in the Asia-Pacific region between 2010 and 2015

Anthropogenic emissions in the Asia-Pacific region have changed rapidly in recent years due to increasing industrialization and mobility, as well as the implementation of emission abatement controls. These changes are likely to have affected the region's burden of premature mortalities associated with exposure to fine particulate matter (PM2.5). However, the contribution of each sector and effectiveness of different policy measures has not yet been quantified. As such, this study estimates changes in regional anthropogenic emissions by sector between 2010 and 2015. These changes are combined with an existing high-resolution emissions inventory to estimate emissions for the year 2015. Using a chemistry-transport model, we then estimate (i) the total contribution of each sector to premature mortality in 2015; and (ii) the effects of changes in each sector's contribution to total PM2.5-driven premature mortalities between 2010 and 2015. We estimate that globally, 2,030,000 (95% CI: 1,770,000 to 2,280,000) PM2.5-driven premature mortalities are attributable to anthropogenic emissions in 2015 in Asia-Pacific with the top three sources being the agricultural, industrial, and residential sectors. Between 2010 and 2015, excluding the effects of changes in population distribution or other social factors, sustained growth in economic activity led to an estimated 99,000 (95% CI: 81,000 to 130,000) additional premature mortalities annually, primarily across India, Indonesia, and Bangladesh. Simultaneously, changes such as electrification of railroads and newly-introduced abatement measures, e.g. China's Action Plan on the Prevention and Control of Air Pollution, region-wide adoption of Euro IV/V/VI-compliant road vehicles, and implementation of fuel quality standards, resulted in an estimated total reduction of 76,000 (95% CI: 65,000 to 100,000) annual premature mortalities, primarily across East Asia, including China and Japan. These opposing drivers add to a net change of an additional 22,000 (95% CI: 12,000 to 33,000) PM2.5-driven annual premature mortalities between 2010 and 2015 associated with anthropogenic combustion emissions in Asia-Pacific.

Biomonitoring trace element contamination impacted by atmospheric deposition in China's remote mountains

The purpose of this study is to better understand the key driving factors affecting the distribution of trace elements in remote mountainous areas at a national scale. In this regard, eight trace elements (As, Cd, Cr, Cu, Ni, Pb, Sb, Zn) in mosses were investigated at thirty remote mountains across China. The sources and possible factors controlling the distribution of trace elements in the mosses were identified through multivariate statistical analysis and Pb isotopic ratios. The results showed that the concentrations of trace elements in the mosses were higher than the levels in most European countries but comparable to those in Chinese cities. Mosses had the highest concentration levels of Cd and Sb and slightly lower levels of other trace elements. Spatially, moss contamination with the trace elements was significantly higher in the eastern, southern and southwestern China than in other regions. Mining-related activities, fuel combustion and other industrial emissions were identified as the main anthropogenic sources of As, Cd, Pb, Sb and Zn, whereas Cr, Cu and Ni were mainly from natural sources. The precipitation from monsoons clearly altered the distribution of anthropogenic elements in the mosses. The results of this study indicate that the trace elements in the mosses of China's remote mountains were affected by regional anthropogenic emissions, and the monsoon-dominated trace element transport and deposition should be highlighted at a large regional scale. These findings provide baseline data for future targeting policies to protect remote ecosystems from long-term inputs of trace elements via long-range atmospheric transportation.

Recent developments of anthropogenic air pollutant emission inventories in Guangdong province, China

Emission inventory (EI) requires continuous updating to improve its quality and reduce its uncertainty. In this study, recent developments on source classification, emission methods, emission factors and spatial-temporal surrogates in the Guangdong regional anthropogenic emission inventory are presented. The developments include: ~40 additional emission sources in a re-classified source classification system, >50 improved spatial and temporal surrogates, 85% of local/domestic emission factors used, and updated estimation methods of on-road mobile, marine, and solvent use sources. The developments were updated to the recent 2012-based high resolution emission inventories, and their results were compared with previous 2006- and 2010-based emission inventories. The results indicated: (1) The total SO2, NOx, CO, PM10, PM2.5, BC, OC, VOCs and NH3 emissions in 2012 were 777.0kt, 1532.2kt, 7305.4kt, 1176.4kt, 480.9kt, 54.2kt, 79.9kt, 1255.1kt and 584.1kt, respectively, for Guangdong province, with higher emission densities observed in the central PRD region. (2) No great changes on source structures were found among three years, but their contributions varied. (3) SO2, PM10 and PM2.5 emissions showed downward trends, likely a result of strict control measures on power plant and industrial combustion sources. (4) NOx emission exhibited relatively stable levels in 2010 and 2012, but contributions from industrial, on-road and non-road mobile sources increased. (5) VOCs emissions showed an upward trend, mainly resulting from dramatically increased light-duty passenger car population and solvent use. (6) Spatial and temporal allocations were updated with constant improvements of spatial and temporal surrogates. (7) Uncertainty ranges of emission estimates were reduced, indicating that the 2012-based PRD regional EI are more reliable. The work shown in this study can be a reference example for other regions to continuously update their emission inventories.

Influence of anthropogenic emissions and boundary conditions on multi-model simulations of major air pollutants over Europe and North America in the framework of AQMEII3.

In the framework of the third phase of the Air Quality Model Evaluation International Initiative (AQMEII3), and as contribution to the second phase of the Hemispheric Transport of Air Pollution (HTAP2) activities for Europe and North America, the impacts of a 20 % decrease of global and regional anthropogenic emissions on surface air pollutant levels in 2010 are simulated by an international community of regional-scale air quality modeling groups, using different state-of-the-art chemistry and transport models (CTMs). The emission perturbations at the global level, as well as over the HTAP2-defined regions of Europe, North America and East Asia, are first simulated by the global Composition Integrated Forecasting System (C-IFS) model from European Centre for Medium-Range Weather Forecasts (ECMWF), which provides boundary conditions to the various regional CTMs participating in AQMEII3. On top of the perturbed boundary conditions, the regional CTMs used the same set of perturbed emissions within the regional domain for the different perturbation scenarios that introduce a 20 % reduction of anthropogenic emissions globally as well as over the HTAP2-defined regions of Europe, North America and East Asia.Results show that the largest impacts over both domains are simulated in response to the global emission perturbation, mainly due to the impact of domestic emission reductions. The responses of NO2, SO2 and PM concentrations to a 20 % anthropogenic emission reduction are almost linear (~ 20 % decrease) within the global perturbation scenario with, however, large differences in the geographical distribution of the effect. NO2, CO and SO2 levels are strongly affected over the emission hot spots. O3 levels generally decrease in all scenarios by up to ~ 1 % over Europe, with increases over the hot spot regions, in particular in the Benelux region, by an increase up to ~ 6 % due to the reduced effect of NOx titration. O3 daily maximum of 8 h running average decreases in all scenarios over Europe, by up to ~ 1 %. Over the North American domain, the central-to-eastern part and the western coast of the US experience the largest response to emission perturbations. Similar but slightly smaller responses are found when domestic emissions are reduced. The impact of intercontinental transport is relatively small over both domains, however, still noticeable particularly close to the boundaries. The impact is noticeable up to a few percent, for the western parts of the North American domain in response to the emission reductions over East Asia. O3 daily maximum of 8 h running average decreases in all scenarios over north Europe by up to ~ 5 %. Much larger reductions are calculated over North America compared to Europe.In addition, values of the Response to Extra-Regional Emission Reductions (RERER) metric have been calculated in order to quantify the differences in the strengths of nonlocal source contributions to different species among the different models. We found large RERER values for O3 (~ 0.8) over both Europe and North America, indicating a large contribution from non-local sources, while for other pollutants including particles, low RERER values reflect a predominant control by local sources. A distinct seasonal variation in the local vs. non-local contributions has been found for both O3 and PM2.5, particularly reflecting the springtime long-range transport to both continents.

Assessment of atmospheric CO<sub>2</sub> concentration enhancement from anthropogenic emissions based on satellite observations

Anthropogenic CO2 emissions are the dominant factor driving atmospheric CO2 concentration enhancement. However, the magnitude of the increase of CO2 concentration due to regional anthropogenic emissions remains unclear. Satellite-derived observations of atmospheric CO2 concentration provide a promising and effective means by which to monitor and evaluate regional anthropogenic CO2 emissions. This study used the column-averaged dry air mole fraction of CO2 (XCO2) derived from the observations of the greenhouse gases observation satellite (GOSAT) to assess quantitatively the effect of anthropogenic emissions on CO2 enhancement in two study areas located within the same latitudinal zone (35°–50°N): one in northern China and the other in the eastern USA. The study collected original XCO2 data (v02.xx) from a five-year period (2010–2014), released by the GOSAT project of the National Institute for Environmental Studies in Japan. Two high-density urban areas were selected as anthropogenic emission regions (emission-regions). These areas comprised the Beijing-Tianjin-Hebei area centered on Beijing (43 million square kilometers) in northern China and the urban agglomeration that includes New York City (55 million square kilometers) in the eastern USA, for which the magnitudes of anthropogenic CO2 emissions were about 950 and 1312 Tg CO2/a, respectively, according to the CO2 emission inventory in 2010 released by the Carbon Dioxide Information Analysis Center (CDIAC). Two regions with lower emissions, considered as background-regions for comparison with the emission-regions, were prepared according to the distribution of potential temperature and CO2 emission data from CDIAC, where anthropogenic CO2 emissions in 2010 were about 127 and 123 Tg CO2/a, respectively. The yearly averaged XCO2 data were calculated based on the seasonally averaged XCO2 data using the original GOSAT XCO2 retrievals from the four regions. In comparison with the background-regions, the results showed the enhancements of CO2 concentration in the emission-regions were, on average, 1.8 and 2.0 ppm in the Beijing-Tianjin-Hebei area and urban agglomeration in the USA, respectively. The maximum and minimum enhancements in China were 2.4 ppm in 2010 and 1.3 ppm in 2014, respectively. The maximum and minimum enhancements in the USA were 2.6 ppm in 2012 and 1.6 ppm in 2010, respectively. Moreover, the enhancements were highest in winter (2.4±0.6 and 2.8±0.8 ppm in China and the USA, respectively). Intriguingly, analysis of the monthly variations revealed that CO2 concentration in the Beijing-Tianjin-Hebei area decreased anomalously by 3.2 ppm during the Asia-Pacific Economic Cooperation (APEC) summit in November 2014 compared with the period before the summit. This anomalous drop probably reflects the effects of the artificial control of CO2 emissions implemented by the government during the APEC summit in order to improve air quality. The above enhancements of CO2 concentration prefer to be slightly less than the actual enhancements of CO2 concentration induced by anthropogenic emissions due to bio-ecological flux in the emission-regions. Based on an investigation of bio-ecological flux in the Beijing-Tianjin-Hebei area in earlier researches, the actual CO2 enhancement induced by anthropogenic emissions should be added an increment of less than 0.6 ppm absorbed by the bio-ecological system to the above-mentioned 1.8 ppm enhancement. The study results demonstrate the efficacy of using satellite-derived observations for evaluating the impact of anthropogenic emissions on the enhancement of atmospheric CO2 by analyzing changes in regional CO2 concentration. This provides a promising method with which to verify regional anthropogenic emissions and to support governmental oversight, control, and decision making regarding CO2 emission reduction.

US surface ozone trends and extremes from 1980 to 2014: quantifying the roles of rising Asian emissions, domestic controls, wildfires, and climate

Abstract. US surface O3 responds to varying global-to-regional precursor emissions, climate, and extreme weather, with implications for designing effective air quality control policies. We examine these conjoined processes with observations and global chemistry-climate model (GFDL-AM3) hindcasts over 1980–2014. The model captures the salient features of observed trends in daily maximum 8 h average O3: (1) increases over East Asia (up to 2 ppb yr−1), (2) springtime increases at western US (WUS) rural sites (0.2–0.5 ppb yr−1) with a baseline sampling approach, and (3) summertime decreases, largest at the 95th percentile, and wintertime increases in the 50th to 5th percentiles over the eastern US (EUS). Asian NOx emissions have tripled since 1990, contributing as much as 65 % to modeled springtime background O3 increases (0.3–0.5 ppb yr−1) over the WUS, outpacing O3 decreases attained via 50 % US NOx emission controls. Methane increases over this period contribute only 15 % of the WUS background O3 increase. Springtime O3 observed in Denver has increased at a rate similar to remote rural sites. During summer, increasing Asian emissions approximately offset the benefits of US emission reductions, leading to weak or insignificant observed O3 trends at WUS rural sites. Mean springtime WUS O3 is projected to increase by ∼ 10 ppb from 2010 to 2030 under the RCP8.5 global change scenario. While historical wildfire emissions can enhance summertime monthly mean O3 at individual sites by 2–8 ppb, high temperatures and the associated buildup of O3 produced from regional anthropogenic emissions contribute most to elevating observed summertime O3 throughout the USA. GFDL-AM3 captures the observed interannual variability of summertime EUS O3. However, O3 deposition sink to vegetation must be reduced by 35 % for the model to accurately simulate observed high-O3 anomalies during the severe drought of 1988. Regional NOx reductions alleviated the O3 buildup during the recent heat waves of 2011 and 2012 relative to earlier heat waves (e.g., 1988, 1999). The O3 decreases driven by NOx controls were more pronounced in the southeastern US, where the seasonal onset of biogenic isoprene emissions and NOx-sensitive O3 production occurs earlier than in the northeast. Without emission controls, the 95th percentile summertime O3 in the EUS would have increased by 0.2–0.4 ppb yr−1 over 1988–2014 due to more frequent hot extremes and rising biogenic isoprene emissions.

The contribution of soil biogenic NO and HONO emissions from a managed hyperarid ecosystem to the regional NO<sub><i>x</i></sub> emissions during growing season

Abstract. A study was carried out to understand the contributions of soil biogenic NO emissions from managed (fertilized and irrigated) hyperarid ecosystems in NW China to the regional NOx emissions during the growing season. Soil biogenic net potential NO fluxes were quantified by laboratory incubation of soil samples from the three dominating ecosystems (desert, cotton, and grape fields). Regional biogenic NO emissions were calculated bottom-up hourly for the entire growing season (April–September 2010) by considering corresponding land use, hourly data of soil temperature, gravimetric soil moisture, and fertilizer enhancement factors. The regional HONO emissions were estimated using the ratio of the optimum condition ((FN,opt(HONO) to FN,opt (NO)). Regional anthropogenic NOx emissions were calculated bottom-up from annual statistical data provided by regional and local government bureaus which have been downscaled to monthly value. Regional top-down emission estimates of NOx were derived on the monthly basis from satellite observations (OMI) of tropospheric vertical NO2 column densities and prescribed values of the tropospheric NOx lifetime. In order to compare the top-down and bottom-up emission estimates, all emission estimates were expressed in terms of mass of atomic nitrogen. Consequently, monthly top-down NOx emissions (total) were compared with monthly bottom-up NOx emissions (biogenic + anthropogenic) for the time of the satellite overpass (around 13:00 LT) with the consideration of the diurnal cycle of bottom-up estimates. Annual variation in total Tohsun Oasis NOx emissions is characterized by a strong peak in winter (December–February) and a secondary peak in summer (June–August). During summer, soil biogenic emissions were from equal to double that of related anthropogenic emissions, and grape soils were the main contributor to soil biogenic emissions, followed by cotton soils, while emissions from the desert were negligible. The top-down and bottom-up emission estimates were shown to be useful methods to estimate the monthly/seasonal cycle of the total regional NOx emissions. The resulting total NOx emissions show a strong peak in winter and a secondary peak in summer, and the second maximum in summer was only found if the soil emissions were taken into account, which provides confidence in both completely independent methods. Despite the regional character of these findings, particularly the second maximum in summer provides substantial evidence to hypothesize that biogenic emissions from soils of managed drylands (irrigated and fertilized) in the growing period may be much more important contributors to regional NOx budgets of dryland regions than thought before.

The effects of global change upon United States air quality

Abstract. To understand more fully the effects of global changes on ambient concentrations of ozone and particulate matter with aerodynamic diameter smaller than 2.5 μm (PM2.5) in the United States (US), we conducted a comprehensive modeling effort to evaluate explicitly the effects of changes in climate, biogenic emissions, land use and global/regional anthropogenic emissions on ozone and PM2.5 concentrations and composition. Results from the ECHAM5 global climate model driven with the A1B emission scenario from the Intergovernmental Panel on Climate Change (IPCC) were downscaled using the Weather Research and Forecasting (WRF) model to provide regional meteorological fields. We developed air quality simulations using the Community Multiscale Air Quality Model (CMAQ) chemical transport model for two nested domains with 220 and 36 km horizontal grid cell resolution for a semi-hemispheric domain and a continental United States (US) domain, respectively. The semi-hemispheric domain was used to evaluate the impact of projected global emissions changes on US air quality. WRF meteorological fields were used to calculate current (2000s) and future (2050s) biogenic emissions using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). For the semi-hemispheric domain CMAQ simulations, present-day global emissions inventories were used and projected to the 2050s based on the IPCC A1B scenario. Regional anthropogenic emissions were obtained from the US Environmental Protection Agency National Emission Inventory 2002 (EPA NEI2002) and projected to the future using the MARKet ALlocation (MARKAL) energy system model assuming a business as usual scenario that extends current decade emission regulations through 2050. Our results suggest that daily maximum 8 h average ozone (DM8O) concentrations will increase in a range between 2 to 12 parts per billion (ppb) across most of the continental US. The highest increase occurs in the South, Central and Midwest regions of the US due to increases in temperature, enhanced biogenic emissions and changes in land use. The model predicts an average increase of 1–6 ppb in DM8O due to projected increase in global emissions of ozone precursors. The effects of these factors are only partially offset by reductions in DM8O associated with decreasing US anthropogenic emissions. Increases in PM2.5 levels between 4 and 10 μg m−3 in the Northeast, Southeast, Midwest and South regions are mostly a result of increase in primary anthropogenic particulate matter (PM), enhanced biogenic emissions and land use changes. Changes in boundary conditions shift the composition but do not alter overall simulated PM2.5 mass concentrations.

Characteristics and potential sources of atmospheric mercury at a subtropical near‐coastal site in East China

AbstractTo evaluate the impact of regional mercury (Hg) emissions and understand possible source regions of atmospheric Hg in Eastern China, 2 year observation for speciated atmospheric Hg was conducted at the Dameishan Atmospheric Observatory, a mountain site near the east coast of China. The observed concentration of total gaseous Hg (TGM) was 3.3 ± 1.4 ng m−3. During the sampling period, gaseous oxidized Hg and particulate bound Hg were 6.7 ± 4.3 pg m−3 and 180 ± 110 pg m−3 in winter and 5.9 ± 3.4 pg m−3 and 130 ± 100 pg m−3 in spring, respectively. The relatively high mean concentration of TGM was mainly caused by regional anthropogenic emissions and occasional long‐range transport from domestic source regions. Seasonal variation in the TGM concentration was observed with lower values in the wet monsoon season (from May to September) and higher values in the dry monsoon season (from October to April). Backward trajectories and potential source contribution function analysis suggested that anthropogenic Hg emission from coal combustion in the Yangtze River Delta region was the most likely cause for the elevated TGM concentrations. Relatively clean air originating from the East China Sea was the most possible cause for the observed low TGM concentrations. Positive correlation between TGM concentration and air quality index suggests that emissions that influenced regional air quality contributed to the elevated TGM concentrations.

Observations of atmospheric mercury in China: a critical review

Abstract. China presently contributes the largest amount of anthropogenic mercury (Hg) emission into the atmosphere in the world. Over the past decade, numerous studies have been conducted to characterize the concentration and forms of atmospheric Hg in China, which provide insights into the spatial and temporal distributions of atmospheric Hg through ground-based measurements at widely diverse geographical locations and during cruise and flight campaigns. In this paper, we present a comprehensive review of the state of understanding in atmospheric Hg in China. Gaseous elemental mercury (GEM) and particulate-bound mercury (PBM) measured at the remote sites in China are substantially elevated compared to the background values in the Northern Hemisphere. In Chinese urban areas, the highly elevated GEM, PBM and gaseous oxidized mercury (GOM) were mainly derived from local anthropogenic Hg emissions, whereas regional anthropogenic emissions and long-range transport from domestic source regions are the primary causes of the elevated GEM and PBM concentrations at remote sites. Using 7–9 years of continuous observations at a remote site and an urban site, a slight increase in atmospheric GEM (2.4–2.5 % yr−1) was identified (paired samples test: p < 0.01), which is in agreement with the increasing domestic anthropogenic emissions. Anthropogenic GEM emission quantity in China estimated through the observed GEM / CO concentration ratios ranged from 632 to 1138 t annually over the past decade, 2–3 times larger than published values using emission activity data. Modeling results and filed measurements show dry deposition is the predominant process for removing Hg from the atmosphere, 2.5–9.0 times larger than wet deposition, due to the elevated atmospheric GEM and PBM concentrations that facilitate dry deposition to terrestrial landscapes. Further studies to reconcile the observed and simulated Hg concentrations, to understand the impact of domestic emission reduction on Hg concentration and deposition and to delineate the role of Hg emission and deposition of China in the global Hg biogeochemical cycle, are needed.

Atmospheric transport of ozone between Southern and Eastern Asia

This study describes the effect of pollution transport between East Asia and South Asia on tropospheric ozone (O3) using model results from the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). Ensemble mean O3 concentrations are evaluated against satellite-data and ground observations of surface O3 at four stations in India. Although modeled surface O3 concentrations are 1020ppb higher than those observed, the relative magnitude of the seasonal cycle of O3 is reproduced well. Using 20% reductions in regional anthropogenic emissions, we quantify the seasonal variations in pollution transport between East Asia and South Asia. While there is only a difference of 0.05 to 0.1ppb in the magnitudes of the regional contributions from one region to the other, O3 from East Asian sources affects the most densely populated parts of South Asia while Southern Asian sources only partly affect the populated parts of East Asia. We show that emission changes over East Asia between 2000 and 2010 had a larger impact on populated parts of South Asia than vice versa. This study will help inform future decisions on emission control policy over these regions.