Direct Anthropogenic Emissions Research Articles

Global Warming and Anthropogenic Emissions of Water Vapor.

The two major components of greenhouse gases, CO2 and water, are indispensable for sustaining life on Earth. Water vapor is the most significant greenhouse gas that has provided the earth with an "atmospheric blanket" and prevented the surface of the earth from freezing. However, contemporary climate models largely consider the influence of water vapor as a factor within positive feedback loops, while the possibility of direct anthropogenic emissions of water vapor as primary drivers of global warming remains underexplored. In particular, a common assumption has been that the global atmospheric water vapor will increase by about 6 to 7% in response to each 1 °C of warming caused by the nonaqueous greenhouse gases in accordance with the Clausius-Clapeyron equation, and this increased moisture content will lead to an increased greenhouse gas effect. However, the Clausius-Clapeyron equation is based on two-phase equilibrium, and there is no a priori physical basis that it can be applied to the earth's climate for which the water vapor does not always coexist with a condensed phase. Here, we utilized global specific humidity data from the NCEP/NCAR reanalysis data set to examine whether the Clausius-Clapeyron equation can form a basis for such positive feedback commonly assumed in the contemporary climate models. Our results show (1) qualitiatively, the linear nature of the Clausius-Clapeyron equation demonstrates a significant level of consistency when averaged over expansive regions like specific latitudes around the globe, (2) this consistency does not extend to individual locations where a plot of (ln Pv) vs (1/T) becomes nonlinear, indicating substantial undersaturation that varies with time, (3) quantitatively, the discrepancies between the observed and the expected values of the slopes are wide-ranging, and (4) the absolute amount of water vapor increased substantially above the population centers and the agricultural areas in the Northern Hemisphere between 1960 and 2020. Human activities appear to have substantial impacts on the local water vapor content in the atmosphere. Once we assume that anthropogenic emissions of water vapor are the source of local water vapor content in the atmosphere, it can, together with the air circulation patterns (Hadler, Ferrel and polar), provide an explanation for the observations that Arctic ice has been melting at a much more accelerated rate than Antarctic ice.

Multidimensional Drivers of Mercury Distribution in Global Surface Soils: Insights from a Global Standardized Field Survey.

Soil stores a large amount of mercury (Hg) that has adverse effects on human health and ecosystem safety. Significant uncertainties still exist in revealing environmental drivers of soil Hg accumulation and predicting global Hg distribution owing to the lack of field data from global standardized analyses. Here, we conducted a global standardized field survey and explored a holistic understanding of the multidimensional environmental drivers of Hg accumulation in global surface soils. Hg content in surface soils from our survey ranges from 3.8 to 618.2 μg kg-1 with an average of 74.0 μg kg-1 across the globe. Atmospheric Hg deposition, particularly vegetation-induced elemental Hg0 deposition, is the major source of surface soil Hg. Soil organic carbon serves as the major substrate for sequestering Hg in surface soils and is significantly influenced by agricultural management, litterfall, and elevation. For human activities, changing land-use could be a more important contributor than direct anthropogenic emissions. Our prediction of a new global Hg distribution highlights the hot spots (high Hg content) in East Asia, the Northern Hemispheric temperate/boreal regions, and tropical areas, while the cold spots (low Hg content) are in arid regions. The holistic understanding of multidimensional environmental drivers helps to predict the Hg distribution in global surface soils under a changing global environment.

Impact of visits on the microclimates of caves, Experimental evidence from Škocjan Caves

Tourism activities in caves can result in changes in the microclimates of caves. The natural microclimate in closed caves is constant due to the balance between cave air and cave walls, while in open caves exchanges with outside air influence the microclimate. Visits to caves, especially in closed smaller caves, can thus endanger the natural balance if the microclimate does not return to natural conditions quickly enough.Continuous monitoring of the temperature and concentration of carbon dioxide in Škocjan Caves enables the assessment of the impact of visits. For this purpose, we used data measured in the relatively closed Silent Cave, at the locations named Calvary (Kalvarija), Tent (Šotor), and Passage (Prehod) in 2016, and in the wide open Murmuring Cave, at the locations named Bridge (Most) and Rimstone Pools (Ponvice), in 2013. The outdoor air temperature, as measured at the Škocjan meteorological station on the surface plateau, was considered in both cases. Along the tourist part of Škocjan Caves, the most closed part of the cave in Silent Cave is the location at Calvary, when the entrance doors through an artificially dug tunnel are closed. During the visits, the microclimate is subjected to draughts through open doors and to anthropogenic emissions. The data suggest that the influence of draughts predominates over direct anthropogenic emissions. In winter or on cold days air flows upwards and through the tunnel out of the cave, whereas in summer or on warm days it flows downwards. In such cases, the CO2 concentration decreases markedly due to the downwards chimney effect as the concentration in the outside air is much lower than in the cave. The data show that the temperature overnight and towards morning always returns to its natural value even in this
 rather small location in the cave. The changes in CO2 concentration persist for a longer period, until the time of the first visit the next morning, when it is again perturbed by a new visit. The data on time courses support the theoretically estimated characteristic of the exponential decline of disturbances backward towards natural conditions, depending on the size of a cave and on the efficiency of exchanges with its walls. For tem­perature, this characteristic time tT is about three to six hours at the Calvary site. The return of CO2 to natural conditions tCO2 is longer and its estimate less reliable than the one for temperature. In the wide-open and large Murmuring Cave, the impact of visits is negligible throughout the year. In this part of the cave we can observe the influence of external daily and annual changes, the amplitudes of which get smaller, and their phase lags bigger, deeper in the cave.

Phase-wise analysis of the COVID-19 lockdown impact on aerosol, radiation and trace gases and associated chemistry in a tropical rural environment

Phase-wise variations in different aerosol (BC, AOD, PM1, PM2.5 and PM10), radiation (direct and diffused) and trace gases (NO, NO2, CO, O3, SO2, CO2 and CH4) and their associated chemistry during the COVID-19 lockdown have been investigated over a tropical rural site Gadanki (13.5° N, 79.2° E), India. Unlike most of the other reported studies on COVID-19 lockdown, this study provides variations over a unique tropical rural environment located at a scientifically strategic location in the Southern Indian peninsula. Striking differences in the time series and diurnal variability have been observed in different phases of the lockdown. The levels of most species that are primarily emitted from anthropogenic activities reduced significantly during the lockdown which also impacted the levels and diurnal variability of secondary species like O3. When compared with the same periods in 2019, short-lived trace gas species such as NO, NO2, SO2 which have direct anthropogenic emission influence have shown the reduction over 50%, whereas species like CO and O3 which have direct as well as indirect impacts of anthropogenic emissions have shown reductions up to 10%. Long-lived species (CO2 and CH4) have shown negligible difference (<1%). BC and AOD have shown reductions over 20%. Particulate Matter (1, 2.5 and 10) reductions have been in the range of 40 to 50% when compared to the pre-lockdown period. The changes in shortwave downward radiation at the surface, diffuse component due to the scattering and diffuse fraction have been +2.2%, −4.1% and −2.4%, respectively, in comparison with 2019. In contrast with the studies over urban environments, air quality category over the rural environment remained same during the lockdown despite reduction in pollutants level. All the variations observed for different species and their associated chemistry provides an excellent demonstration of rural atmospheric chemistry and its intrinsic links with the precursor concentrations and dynamics.

Total OH Reactivity of Emissions from Humans: In Situ Measurement and Budget Analysis.

Humans are a potent, mobile source of various volatile organic compounds (VOCs) in indoor environments. Such direct anthropogenic emissions are gaining importance, as those from furnishings and building materials have become better regulated and energy efficient homes may reduce ventilation. While previous studies have characterized human emissions in indoor environments, the question remains whether VOCs remain unidentified by current measuring techniques. In this study conducted in a climate chamber occupied by four people, the total OH reactivity of air was quantified, together with multiple VOCs measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) and fast gas chromatography–mass spectrometry (fast-GC–MS). Whole-body, breath, and dermal emissions were assessed. The comparison of directly measured OH reactivity and that of the summed reactivity of individually measured species revealed no significant shortfall. Ozone exposure (37 ppb) was found to have little influence on breath OH reactivity but enhanced dermal OH reactivity significantly. Without ozone, the whole-body OH reactivity was dominated by breath emissions, mostly isoprene (76%). With ozone present, OH reactivity nearly doubled, with the increase being mainly caused by dermal emissions of mostly carbonyl compounds (57%). No significant difference in total OH reactivity was observed for different age groups (teenagers/young adults/seniors) without ozone. With ozone present, the total OH reactivity decreased slightly with increasing age.

Distribution of surface carbon monoxide over the Indian subcontinent: Investigation of source contributions using WRF-Chem

This study investigates fractional contribution of different carbon monoxide (CO) sources over the Indian subcontinent at the surface in 2015 using a tagged tracer approach in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Model simulations are evaluated with respect to in-situ and satellite observations. The simulated CO levels reproduced in-situ observations in Pune, Anantapur, Udaipur, Ahmedabad, and Chennai reasonably well with mean bias ranging from −89.9 to 87.0 ppbv and RMSE ranging from 28 to 40% but a poor model performance was noticed in Hyderabad, Jabalpur, and Kanpur with larger mean bias (−259.0–190.9 ppbv) and RMSE (45–96%). Simulated CO concentrations are also compared with CO retrieved by MOPITT at 800 hPa and 200 hPa. At 800 hPa (200 hPa), the annual average WRF-Chem CO varies from 195 ± 69 to 224 ± 93 ppbv (102 ± 25 to 136 ± 21 ppbv) while MOPITT CO varies from 103 ± 26 to 114 ± 29 ppbv (103 ± 30 to 134 ± 33) over different Indian sub-regions. Over most of the regions, good correlation (coefficient of correlation > 0.7) is observed between simulated and satellite observed CO with mean bias of 92–118 ppbv at 800 hPa and −4 to 3 ppbv at 200 hPa. Over the total Indian region, we find the highest contribution from anthropogenic emissions (CO-ANT) and inflow into the model domain from domain boundaries (CO-BACK) with 45–46% contribution each and very small contribution (<5%) of biomass burning (CO-BIOM), biogenic (CO-BIOG) emissions, and photochemical production (CO-CHEM). Fractional contribution of these tracers are analysed over different Indian sub-regions. CO-ANT (21–69%) and CO-BACK (22–66%) contributions are found high throughout the year over all the Indian landmass regions. CO-BACK contribution is found to be maximum (70–95%) over the Bay of Bengal and Arabian Sea. During winter season, CO-ANT and CO-BACK contribute 32–69% and 27–56% respectively over landmass regions of India. During spring, highest CO-BACK (66%) over Western India as compared to other landmass regions is attributed to CO inflow from the Arabian Peninsula and Middle East region. CO-BIOM contributes more than 22% in NE&M (North-East India and Myanmar) during spring due to slash and burn agriculture practice. During summer, transport of cleaner marine air and stronger vertical mixing are major causes of lower CO concentration over all sub-regions. During autumn, CO-ANT contributes 33–70% over different landmass regions. Surface CO concentration is found to be mainly controlled by the direct anthropogenic emission in Indian megacities with a contribution exceeding 70% to CO in Delhi and Kolkata throughout the year.

Primary Suppliers Driving Atmospheric Mercury Emissions through Global Supply Chains

•Global atmospheric mercury emissions embodied in trade are uncovered•China, Indonesia, and India are major primary suppliers causing Hg emissions•Primary inputs of Australia, the US, and Japan mainly cause Hg emissions in China•Critical supply-chain paths inducing global atmospheric Hg emissions are revealed Mercury poisoning is highly detrimental to life. Minamata disease, a result of severe mercury poisoning, has claimed thousands of lives, yet mercury is still released into the environment today. The Minamata Convention on Mercury, adopted in 2013, requires signatories to enact measures to control mercury pollution. Current measures focus on controlling direct mercury emissions from production activities within individual nations. However, emissions are partly driven by primary inputs of foreign nations through global supply chains. Identifying the production point is insufficient. This study uncovers atmospheric mercury emissions from the supply perspective for the year 2015. Results show that the most critical primary suppliers are China, Indonesia, and India, and critical industries relate to resource extraction and power generation. The outcome can help support supply-side policy decisions, including optimization of structures of labor and capital inputs, adjustment of tax rates and subsidies, and contributions to global regulations, such as establishing mechanisms of financial aid and international cooperation. 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. 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. Mercury (Hg) emissions to the atmosphere have adverse impacts on human beings and ecosystems. The methylation of Hg can produce methylmercury (MeHg), which is severely detrimental to life.1Chen L. Liang S. Liu M. Yi Y. Mi Z. Zhang Y. Li Y. Qi J. Meng J. Tang X. et al.Trans-provincial health impacts of atmospheric mercury emissions in China.Nat. 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Globalization fragments the primary inputs (e.g., inputs of labor and capital), production, and final consumption activities into different regions. Goods and services produced by local regions can be directly or indirectly traded to final consumers of external regions through global supply chains. Moreover, local production can be directly or indirectly caused by primary inputs of external regions through global supply chains. Thus, direct geographic emissions from production activities of a nation are usually partly caused by the final consumption of other nations28Davis S.J. Caldeira K. Consumption-based accounting of CO2 emissions.Proc. Natl. Acad. Sci. USA. 2010; 107: 5687-5692Crossref PubMed Scopus (1207) Google Scholar, 29Liang S. Wang Y. Cinnirella S. Pirrone N. Atmospheric mercury footprints of nations.Environ. Sci. Technol. 2015; 49: 3566-3574Crossref PubMed Scopus (104) Google Scholar or by primary inputs of other nations30Liang S. Qu S. Zhu Z. Guan D. Xu M. 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They can support more specific supply-side and demand-side measures. For example, critical supply-chain paths can identify preferential downstream users for the optimization of product-allocation behaviors. They can also identify preferential upstream suppliers for the optimization of consumption behaviors and productivity improvement measures.41Liang S. Zhang C. Wang Y. Xu M. Liu W. Virtual atmospheric mercury emission network in China.Environ. Sci. Technol. 2014; 48: 2807-2815Crossref PubMed Scopus (97) Google Scholar, 44Liang S. Guo S. Newell J.P. Qu S. Feng Y. Chiu A.S.F. Xu M. Global drivers of Russian timber harvest.J. Ind. Ecol. 2016; 20: 515-525Crossref Scopus (39) Google Scholar, 45Liang S. Wang Y. Zhang T. Yang Z. Structural analysis of material flows in China based on physical and monetary input-output models.J. Clean. Prod. 2017; 158: 209-217Crossref Scopus (44) Google Scholar, 46Wang J. Du T. Wang H. Liang S. Xu M. Identifying critical sectors and supply chain paths for the consumption of domestic resource extraction in China.J. Clean. Prod. 2019; 208: 1577-1586Crossref Scopus (29) Google Scholar Moreover, these supply-chain paths can be used for assessing how policy interventions in a sector are transferred across the whole supply chains. However, such critical supply-chain paths driving global atmospheric Hg emissions have not been investigated in existing studies. This study analyzes income-based atmospheric Hg emissions of nations and sectors by using the global environmentally extended multi-regional input-output (EE-MRIO) model. We also reveal critical supply-chain paths driving global atmospheric Hg emissions by the structural path analysis (SPA) based on the global EE-MRIO model. Moreover, we compare income-based results with production-based and consumption-based results and find that income-based results can uncover new findings and policy implications for global Hg control. Results show that, from the supply viewpoint, China, Indonesia, and India are major primary suppliers causing global atmospheric Hg emissions, and major sectors and critical supply-chain paths are related to resource extraction and power generation. Figure 1A shows that China, Indonesia, and India (followed by Colombia, Peru, Russian Federation [Russia], and the United States [US]) were the top three primary suppliers causing global atmospheric Hg emissions in 2015. Income-based atmospheric Hg emissions of China were 465 tons, occupying 21.5% of the global total. Income-based atmospheric Hg emissions of Indonesia and India were 113 tons (5.2% of the global total) and 100 tons (4.6% of the global total), respectively. Figure 1A also shows the differences among income-based, production-based, and consumption-based atmospheric Hg emissions of nations, reflecting the differences in the degrees of importance for each nation’s role in global supply chains. China’s production-based and consumption-based atmospheric Hg emissions are larger than its income-based emissions. This indicates that, in terms of atmospheric Hg emissions, China is more important as a direct emitter and a final consumer than as a primary supplier. Income-based atmospheric Hg emissions of Indonesia, Colombia, and Peru are close to their production-based emissions. Consumption-based atmospheric Hg emissions of India, the US, Japan, and Germany are larger than their production-based and income-based emissions, reflecting their more important roles as final consumers than as direct emitters and primary suppliers. In global supply chains, Russia, Brazil, South Africa, Kazakhstan, Australia, and Chile are more important as primary suppliers than as direct emitters and final consumers. Russia is a major resource supplier in the world. Its resource supply leads to downstream production and associated atmospheric Hg emissions. Its income-based atmospheric Hg emissions were 69 tons in 2015, 12% higher than its production-based emissions and 53% higher than its consumption-based emissions. Brazil, South Africa, and Kazakhstan are large exporters of fossil fuels, metal ores, and minerals. Their income-based atmospheric Hg emissions were 45%, 30%, and 33% higher than their consumption-based emissions, respectively. Australia exports a large number of minerals and metal ores, and its income-based atmospheric Hg emissions (19 tons) were 145% higher than its production-based emissions (8 tons). For Chile, the income-based emissions (13 tons) were 47% higher than its consumption-based emissions (9 tons). Figure 1B shows income-based atmospheric Hg emissions of sectors. Sectors with large income-based atmospheric Hg emissions are generally related to basic materials and basic services. For example, the “mining and quarrying of non-energy-producing product” sector has the largest income-based atmospheric Hg emissions (629 tons, occupying 29% of the global total) because natural resources from this sector (e.g., metal ores and minerals) are essential to most of the downstream industries discharging atmospheric Hg. These natural resources are mostly allocated to intermediate producers rather than final consumers. Therefore, income-based atmospheric Hg emissions of the “mining and quarrying of non-energy-producing product” sector are significantly higher than its consumption-based emissions. The “electricity, gas, water supply, sewerage, waste, and remediation service” and “mining and extraction of energy-producing product” sectors are ranked second and third, respectively, in income-based results because energy sources are also essential to downstream industrial emitters. Sectors producing finished products, such as construction, machinery, equipment, and public and social services, have higher consumption-based atmospheric Hg emissions than production-based and income-based emissions because the products of these sectors are mainly purchased by final consumers. At the nation-sector level (Figure 1C), nation sectors with the largest income-based atmospheric Hg emissions include the “mining and quarrying of non-energy-producing product” sector of the rest of the world (RoW), the “electricity, gas, water supply, sewerage, waste, and remediation service” sector of the RoW, the “mining and extraction of energy-producing product” sector of the RoW, the “mining and quarrying of non-energy-producing product” sector of Indonesia, and the “electricity, gas, water supply, sewerage, waste, and remediation service” sector of China. It is worth noting that the “financial and insurance activity” sector of China ranked 119th and 261st in production-based and consumption-based results but 14th in income-based results (Figure S1). The “financial and insurance activity” sector is an intermediate stage of the global supply chains. It has a small amount of direct atmospheric Hg emissions, and most of its products are not consumed by final consumers. However, its financial investment is essential to other sectors and causes downstream production and associated atmospheric Hg emissions. Figure 2 shows the sectoral composition of each nation’s income-based, production-based, and consumption-based results. Sectors with large production-based atmospheric Hg emissions are closely related to fossil fuel combustion, mineral ore mining and smelting, and waste-treatment activities, such as the “electricity, gas, water supply, sewerage, waste, and remediation service,” “mining and quarrying of non-energy-producing product,” and “basic metal” sectors. Sectors with large consumption-based emissions mainly produce finally consumed products, such as the “construction" and "electricity, gas, and water” sectors and sectors related to the manufacturing of machinery and equipment. The final consumption of products from these sectors drives large amounts of upstream atmospheric Hg emissions. Sectors with large income-based emissions are mainly associated with resource extraction, energy and power production, the production of basic materials, and commercial services, such as the “mining and quarrying of non-energy-producing product,” “mining and extraction of energy-producing product,” “electricity, gas, water supply, sewerage, waste, and remediation service,” “basic metal,” and “other business sector service” sectors. Their primary inputs cause large amounts of downstream atmospheric Hg emissions. There are obvious differences in the sectoral structure of income-based Hg emissions between nations that are members of the Organization for Economic Co-operation and Development (OECD nations) and nations that are not (non-OECD nations). For non-OECD nations, sectors producing fossil fuels, metal ores, and other minerals have relatively large proportions in income-based Hg emissions. Resources extracted in non-OECD nations cause large amounts of downstream production activities and atmospheric Hg emissions through global supply chains. These resource-extraction sectors are generally not important in OECD nations. International trade leads to the flows of atmospheric Hg emissions embodied in commodity trade. The differences in embodied atmospheric Hg flows between exports and imports are defined as the net embodied Hg flows in this study. Figure 3 shows the major net international embodied Hg flows from direct Hg emitters to primary suppliers (Figure 3A) and from direct Hg emitters to final consumers (Figure 3B) in 2015. Figure 3A shows that Australia-China was the most significant international supplier-emitter pair for global atmospheric Hg emissions in 2015 with 6.9 tons of net embodied Hg flows. Primary inputs of Australia caused 7.0 tons of atmospheric Hg emissions in China in 2015, where the primary contributors were the “mining and quarrying of non-energy-producing product,” “wholesale and retail trade,” and “mining and extraction of energy-producing product” sectors of Australia (occupying 42%, 10%, and 9%, respectively, as Figure 4 shows). This finding can be validated by the significant volumes of resource trade between Australia and China. US-China was the second-most-significant international pair, and its net embodied Hg flows were 5.6 tons. Primary inputs of the US caused 6.1 tons of atmospheric Hg emissions in China, where the primary contributors were the “wholesale and retail trade,” “other business sector service,” and “chemical and pharmaceutical product” sectors of the US (Figure 4). Japan-China ranked third with 3.9 tons of net embodied Hg flows. Primary inputs of Japan caused 4.2 tons of atmospheric Hg emissions in China, and the major primary suppliers were the “wholesale and retail trade,” “chemical and pharmaceutical product,” and “basic metal” sectors of Japan. Other significant international supplier-emitter pairs included Saudi Arabia-China (net 3.4 tons), South Korea-China (net 3.1 tons), Saudi Arabia-India (net 2.2 tons), Germany-China (net 2.1 tons), and Russia-China (net 2.0 tons). We also investigated the major net international embodied Hg flows from direct Hg emitters to final consumers in 2015 (Figure 3B). We observed significant differences in net international embodied Hg flows between income-based results (Figure 3A) and consumption-based results (Figure 3B). For example, major international supplier-emitter pairs included Australia-China, US-China, Japan-China, Saudi Arabia-China, South Korea-China, Saudi Arabia-India, Germany-China, and Russia-China. However, major international consumer-emitter pairs were US-China, China-Peru, US-Colombia, US-Peru, Japan-Indonesia, Japan-China, India-Indonesia, China-Indonesia, and US-India. The important roles of resource-exporting nations (e.g., Australia, Saudi Arabia, and Russia) as primary suppliers for China can be revealed by income-based results but cannot be uncovered by consumption-based results. Meanwhile, consumption-based results suggest that China is a critical final consumer for Colombia and Peru. However, income-based results reveal that China is not a critical primary supplier for Colomb

Source apportionment of summertime ozone in China using a source-oriented chemical transport model

Contributions of industries, power plants, residential, transportation, open burning, and biogenic sectors to summertime ozone (O3) in China in August 2013 are quantified using an improved O3 source apportionment method implemented in a source-oriented Community Multiscale Air Quality (CMAQ) model. The new O3 source apportionment method attributes in-situ O3 formed in each time step to nitrogen oxides (NOx) and volatile organic compounds (VOCs) with a new attribution scheme that considers NOx-VOC-O3 formation sensitivity in NOx-limited, transition, and VOC-limited regimes (three regimes, 3R). This represents an improvement from the traditional O3 source apportionment models, in which O3 formation sensitivity is divided into two-regimes (2R), either NOx-limited or VOC-limited. An expanded source-oriented gas phase chemical mechanism is developed to concurrently track NOx and primary VOCs and their oxidation products from different sources. The source-resolved NO2 photolysis rates and the NO to NO2 conversion rates by peroxy radicals from the source-oriented chemical mechanism are then used to apportion O3 to NOx (O3_NOx) and VOCs (O3_VOC) from different emission sources.Industries, transportation, power plants and biogenic sources are the major emission sectors to O3. High industrial O3_NOx (8–15 ppb; 20–25% of total O3) is mainly located in north and northeast China, the Yantze River Delta (YRD) and part of the Sichuan Basin (SCB). Transportation O3_NOx accounts for 10–15% of total O3 in most urban areas. Power plants’ contributions to O3_NOx (10–15%) are mostly located in Shanxi, Shaanxi, Ningxia and part of Shandong and Jiangsu. The contribution of soil NOx to O3_NOx is highest in regions in west, central and south China with less direct anthropogenic emission influences. VOC-limited grid cells are mostly located at urban cores and large city clusters in the YRD and Pearl River Delta (PRD) regions. Biogenic and industrial sectors are the most important emission sectors that contribute to O3_VOC, accounting for more than 85% of the O3_VOC in China. In north and east provinces, more than 50% of the O3 is non-background, with the provinces in north China having higher overall O3. The Beijing-Tianjin-Hebei (BTH) region has an area-averaged 8-hr O3 of 75 ppb in August 2013 and about half is non-background. Contributions of industries, transportation, power and biogenic sources to non-background O3 are 37%, 22%, 13% and 23%, respectively. The relative contribution of biogenic emissions to non-background O3 is lower on high 8-hr O3 days. The 2R and 3R approaches show significant differences in assessing the relative importance of O3_NOx and O3_VOC, with the 2-regime approach predicting lower O3_NOx but higher O3_VOC. The new source allocation method for O3_VOC can lead to up to 10% differences for industrial and biogenic sectors.

Estimations of indirect and direct anthropogenic dust emission at the global scale

Dust emission acts as a crucial part in the dust cycle that determines dust related processes at both regional and global scale, such as long-range transport, dry/wet deposition, and radiation forcing. However, most dust emission simulations utilizing dust emission scheme merely investigate natural dust, neglecting the contributions of anthropogenic dust induced by direct or indirect anthropogenic activities, resulting in great uncertainties in estimating dust emissions by previous numerical modelling. To comprehensively reproduce the anthropogenic dust emissions process, both “indirect” and “direct” anthropogenic dust emission schemes were constructed to simulate anthropogenic dust emissions originated from diverse kinds of source regions in the study. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) retrievals were utilized as the constraint of anthropogenic dust simulations. Results showed that using both indirect and direct anthropogenic dust emission schemes show good performance on reproducing the spatio-temporal distributions of anthropogenic dust at the global scale during 2007–2010. High value centers of anthropogenic dust emission fluxes locate in India, the east of China, North America, and Africa. Compared with natural dust emissions, indirect anthropogenic dust emissions show an indistinctive seasonal variation, with seasonal differences generally less than 0.42 μg m−2 s−1. Among indirect anthropogenic dust emissions, pasturelands produce more anthropogenic dust particles emission into the atmosphere than croplands at approximately 0.28 μg m−2 s−1, contributing 75.9% of indirect anthropogenic dust emissions. The developing regions emit much higher direct anthropogenic dust emissions than those from developed regions. This study reveals the non-negligible environmental problems especially in urban areas due to anthropogenic dust.

Modeling the global atmospheric transport and deposition of mercury to the Great Lakes

Abstract Mercury contamination in the Great Lakes continues to have important public health and wildlife ecotoxicology impacts, and atmospheric deposition is a significant ongoing loading pathway. The objective of this study was to estimate the amount and source-attribution for atmospheric mercury deposition to each lake, information needed to prioritize amelioration efforts. A new global, Eulerian version of the HYSPLIT-Hg model was used to simulate the 2005 global atmospheric transport and deposition of mercury to the Great Lakes. In addition to the base case, 10 alternative model configurations were used to examine sensitivity to uncertainties in atmospheric mercury chemistry and surface exchange. A novel atmospheric lifetime analysis was used to characterize fate and transport processes within the model. Model-estimated wet deposition and atmospheric concentrations of gaseous elemental mercury (Hg(0)) were generally within ∼10% of measurements in the Great Lakes region. The model overestimated non-Hg(0) concentrations by a factor of 2–3, similar to other modeling studies. Potential reasons for this disagreement include model inaccuracies, differences in atmospheric Hg fractions being compared, and the measurements being biased low. Lake Erie, downwind of significant local/regional emissions sources, was estimated by the model to be the most impacted by direct anthropogenic emissions (58% of the base case total deposition), while Lake Superior, with the fewest upwind local/regional sources, was the least impacted (27%). The U.S. was the largest national contributor, followed by China, contributing 25% and 6%, respectively, on average, for the Great Lakes. The contribution of U.S. direct anthropogenic emissions to total mercury deposition varied between 46% for the base case (with a range of 24–51% over all model configurations) for Lake Erie and 11% (range 6–13%) for Lake Superior. These results illustrate the importance of atmospheric chemistry, as well as emissions strength, speciation, and proximity, to the amount and source-attribution of mercury deposition.

Coupling atmospheric mercury isotope ratios and meteorology to identify sources of mercury impacting a coastal urban‐industrial region near Pensacola, Florida, USA

AbstractIdentifying the anthropogenic and natural sources of mercury (Hg) emissions contributing to atmospheric mercury on local, regional, and global scales continues to be a grand challenge. The relative importance of various direct anthropogenic emissions of mercury, in addition to natural geologic sources and reemission of previously released and deposited mercury, differs regionally and temporally. In this study, we used local‐scale, mesoscale, and synoptic‐scale meteorological analysis to couple the isotopic composition of ambient atmospheric mercury with potential sources of mercury contributing to a coastal urban‐industrial setting near a coal‐fired power plant in Pensacola, Florida, USA. We were able to broadly discern four influences on the isotopic composition of ambient atmospheric mercury impacting this coastal urban‐industrial region: (1) local to regional urban‐industrial anthropogenic emissions (mean δ202Hg = 0.44 ± 0.05‰, 1SD, n = 3), (2) marine‐influenced sources derived from the Gulf of Mexico (mean δ202Hg = 0.77 ± 0.15‰, 1SD, n = 4), (3) continental sources associated with north‐northwesterly flows from within the planetary boundary layer (mean δ202Hg = 0.65 ± 0.04‰, 1SD, n = 3), and (4) continental sources associated with north‐northeasterly flows at higher altitudes (i.e., 2000 m above ground level; mean δ202Hg = 1.10 ± 0.21‰, 1SD, n = 8). Overall, these data, in conjunction with previous studies, suggest that the background global atmospheric mercury pool is characterized by moderately positive δ202Hg values; that urban‐industrial emissions drive the isotopic composition of ambient atmospheric mercury toward lower δ202Hg values; and that air‐surface exchange dynamics across vegetation and soils of terrestrial ecosystems drive the isotopic composition of ambient atmospheric mercury toward higher positive δ202Hg values. The data further suggest that mass‐independent fractionation (MIF) of both even‐mass‐ and odd‐mass‐number isotopes, likely generated by photochemical reactions in the atmosphere or during reemission from terrestrial and aquatic ecosystems, can be obscured by mixing with anthropogenic emissions having different MIF signatures.

Importance of direct anthropogenic emissions of formic acid measured by a chemical ionisation mass spectrometer (CIMS) during the Winter ClearfLo Campaign in London, January 2012

Formic acid, an ubiquitous trace gas in the atmosphere, was measured using a chemical ionisation mass spectrometer (CIMS) during the winter ClearfLo campaign in London, 2012. Daily calibrations of formic acid gave sensitivities of 3 ion counts s−1 pptv−1 for the complete campaign and a limit of detection of 2 ppt. No correlation with nitric acid was observed, R2 of 0.137, indicating no significant secondary source of formic acid. However, a strong positive correlation with NOx, CO, and production in line with rush hour periods indicated a direct anthropogenic emission of formic acid from vehicle emissions. Peaks of 6.7 ppb of formic acid were observed with a mean of 610 ppt. Global models indicated that this emission source dominates in the northern hemisphere where global models underestimate formic acid most significantly, thus increasing the accuracy of modelling of global formic acid emissions.

Characterizations of wet mercury deposition to a remote islet (Pengjiayu) in the subtropical Northwest Pacific Ocean

Thirty-four weekly rainwater samples were collected in 2009 at Pengjiayu, a remote islet in the subtropical Northwest (NW) Pacific Ocean, to study the distribution of rainwater mercury (Hg) concentrations and associated wet deposition fluxes. This is the first study concerning wet Hg deposition to the subtropical NW Pacific Ocean downwind of the East Asian continent, which is the major source region for Hg emissions worldwide. Sample Hg concentrations ranged from 2.25 to 22.33 ng L−1, with a volume-weighted mean (VWM) concentration of 8.85 ng L−1. The annual wet Hg deposition flux was 10.18 μg m−2, about 2.5 times the fluxes measured at sites on the Pacific coast of the USA, supporting the hypothesis that deposition is higher in the western than in the eastern Pacific. Seasonal VWM concentrations were 7.23, 11.58, 7.82, and 9.84 ng L−1, whereas seasonal wet deposition fluxes were 2.14, 3.45, 2.38, and 2.21 μg m−2, for spring, summer, fall and winter, respectively. Higher summer wet Hg deposition was a function of both higher rainwater Hg concentration and greater rainfall. The seasonal pattern of rainwater Hg concentrations was the opposite of the general seasonal pattern of the East Asian air pollutant export. Since there is no significant anthropogenic Hg emission source on the islet of Pengjiayu, the observed high summertime rainwater Hg concentration hints at the importance of Hg0 oxidation and/or scavenging of upper-altitude reactive gaseous Hg (RGM) by deep convection. Direct anthropogenic RGM emissions from the East Asian continent may not contribute significantly to the rainwater Hg concentrations, but anthropogenic Hg0 emissions could be transported to the upper troposphere or marine boundary layer (MBL) where they can be oxidized to produce RGM, which will then be effectively scavenged by cloud water and rainwater.

Observational constraints on the global atmospheric budget of ethanol

Abstract. Energy security and climate change concerns have led to the promotion of biomass-derived ethanol, an oxygenated volatile organic compound (OVOC), as a substitute for fossil fuels. Although ethanol is ubiquitous in the troposphere, our knowledge of its current atmospheric budget and distribution is limited. Here, for the first time we use a global chemical transport model in conjunction with atmospheric observations to place constraints on the ethanol budget, noting that additional measurements of ethanol (and its precursors) are still needed to enhance confidence in our estimated budget. Global sources of ethanol in the model include 5.0 Tg yr−1 from industrial sources and biofuels, 9.2 Tg yr−1 from terrestrial plants, ~0.5 Tg yr−1 from biomass burning, and 0.05 Tg yr−1 from atmospheric reactions of the ethyl peroxy radical (C2H5O2) with itself and with the methyl peroxy radical (CH3O2). The resulting atmospheric lifetime of ethanol in the model is 2.8 days. Gas-phase oxidation by the hydroxyl radical (OH) is the primary global sink of ethanol in the model (65%), followed by dry deposition (25%), and wet deposition (10%). Over continental areas, ethanol concentrations predominantly reflect direct anthropogenic and biogenic emission sources. Uncertainty in the biogenic ethanol emissions, estimated at a factor of three, may contribute to the 50% model underestimate of observations in the North American boundary layer. Current levels of ethanol measured in remote regions are an order of magnitude larger than those in the model, suggesting a major gap in understanding. Stronger constraints on the budget and distribution of ethanol and OVOCs are a critical step towards assessing the impacts of increasing the use of ethanol as a fuel.

Odd Isotope Deficits in Atmospheric Hg Measured in Lichens

Redox reactions govern mercury (Hg) concentrations in the atmosphere because fluxes (emissions and deposition), and residence times, are largely controlled by Hg speciation. Recent work on aquatic Hg photoreduction suggested that this reaction produces non-mass dependent fractionation (NMF) and that residual aquatic Hg(II)is characterized by positive delta199Hg and delta201Hg anomalies. Here, we show that atmospheric Hg accumulated in lichens is characterized by NMF with negative delta199Hg and delta201Hg values (-0.3 to -1 per thousand), making the atmosphere and the aquatic environment complementary reservoirs regarding photoreduction and NMF of Hg isotopes. Because few other reactions than aquatic Hg photoreduction induce NMF, photochemical reduction appears to be a key pathway in the global Hg cycle. Based on a NMF isotope mass balance, direct anthropogenic emissions may account for only 50 +/- 10% of atmospheric Hg deposition in an urban area of NE France. Furthermore, isotopic anomalies found in several polluted soils and sediments strongly suggests that an important part of Hg in these samples was affected by photoreactions and has cycled through the atmosphere before being stored in the geological environment. Thus, mercury isotopic anomalies measured in environmental samples may be used to trace and quantify the contribution of source emissions.

YEAR TIME MODULATION OF n-ALKANES, PAH, NITRO-PAH AND ORGANIC ACIDS AT MONTELIBRETTI ROME, ITALY

The organic fraction of airborne particulates was investigated at Montelibretti RM, Italy, over 12 months and n-alkanes, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatics and aliphatic acids were evaluated. The year time modulations were acquired from all groups of compounds, both in quantitative (cumulative concentrations) and qualitative (percent compositions) terms. Some distribution indexes and diagnostic ratio rates drawn from congener abundances provided information about the twin nature (anthropogenic and biogenic) of sources of organic particulate. Briefly, unlike past decades the appearance of the Montelibretti location was that of a site affected overall by local pollution, as a consequence of both direct anthropogenic emissions and secondary oxidized compounds. The occurrence of polycyclic aromatic hydrocarbons (PAHs) seemed to depend overall upon vehicle emission (diesel powered in particular), although a second, unknown source with year time modulation was present, apparently not associated with biomass/wood burning. By contrast, nitro-PAHs were mainly associated to oxidation of parent PAHs. In summer, PAHs were found at concentrations similar to those measured in 1993–1995, whilst in winter they were three times more abundant than previously reported.

Modelling carbon dynamics from urban land conversion: fundamental model of city in relation to a local carbon cycle

BackgroundThe main task is to estimate the qualitative and quantitative contribution of urban territories and precisely of the process of urbanization to the Global Carbon Cycle (GCC). Note that, on the contrary to many investigations that have considered direct anthropogenic emission of CO2(urbanized territories produce ca. 96–98% of it), we are interested in more subtle, and up until the present time, weaker processes associated with the conversion of the surrounding natural ecosystems and landscapes into urban lands. Such conversion inevitably takes place when cities are sprawling and additional "natural" lands are becoming "urbanized".ResultsIn order to fulfil this task, we first develop a fundamental model of urban space, since the type of land cover within a city makes a difference for a local carbon cycle. Hence, a city is sub-divided by built-up, „green" (parks, etc.) and informal settlements (favelas) fractions. Another aspect is a sub-division of the additional two regions, which makes the total number reaching eight regions, while the UN divides the world by six. Next, the basic model of the local carbon cycle for urbanized territories is built. We consider two processes: carbon emissions as a result of conversion of natural lands caused by urbanization; and the transformation of carbon flows by "urbanized" ecosystems; when carbon, accumulated by urban vegetation, is exported to the neighbouring territories. The total carbon flow in the model depends, in general, on two groups of parameters. The first includes the NPP, and the sum of living biomass and dead organic matter of ecosystems involved in the process of urbanization, and namely them we calculate here, using a new more realistic approach and taking into account the difference in regional cities' evolution.ConclusionThere is also another group of parameters, dealing with the areas of urban territories, and their annual increments. A method of dynamic forecasting of these parameters, based on the statistical regression model, was already suggested; nevertheless we shall further develop a new technique based on one idea to use the gamma-distribution. This will allow us to calculate the total carbon balance and to show how urbanization shifts it.

Cold climate during the closest Stage 11 analog to recent Millennia

The early part of marine isotopic Stage 11 near 400,000 years ago provides the closest analog to Holocene insolation levels of any interglaciation during the era of strong 100,000-year climatic cycles. The CH 4 concentration measured in Vostok ice fell to ∼450 ppb, and CO 2 values to ∼250 ppm. These natural decreases contrast with the increases in recent millennia and support the early anthropogenic hypothesis of major gas emissions from late-Holocene farming. During the same interval, δD values fell from typical interglacial to nearly glacial values, indicating a major cooling in Antarctica early in Stage 11. Other evidence suggests that new ice was accumulating during the closest insolation analog to the present day: a major increase in δ 18O atm at Vostok, a similar increase in marine δ 18O values, and re-initiation of ice rafting in the Nordic Sea. The evidence permits extended (>20,000 year) intervals of Stage 11 interglacial warmth in the Antarctic and North Atlantic, yet it also requires that this warmth ended and a new glacial era began when insolation was most similar to recent millennia. The Holocene CO 2 anomaly was produced only in part by direct anthropogenic emissions; over half of the anomaly resulted from the failure of CO 2 values to fall as they had during previous interglaciations because of natural responses, including a sea-ice advance in the Antarctic and ice-sheet growth in the northern hemisphere.

Carbonyl compounds in boreal coniferous forest air in Hyytiälä, Southern Finland

Abstract. A variety of C1-C12 carbonyl compounds were measured in the air of a boreal coniferous forest located in Hyytiälä, Southern Finland. 24-hour samples were collected during March and April in 2003 using DNPH (2,4-dinitrophenyl hydrazine) coated C18-cartridges and analyzed by liquid chromatography-mass spectrometry (LC-MS). Altogether 22 carbonyl compounds were quantified. The most abundant carbonyls were acetone (24-hour average 1340ng/m3), formaldehyde (480ng/m3) and acetaldehyde (360ng/m3). Concentrations of monoterpene reaction products nopinone (9ng/m3) and limona ketone (5ng/m3) were low compared to the most abundant low molecular weight carbonyls. Trajectory analysis showed that highest concentrations of carbonyls were measured in the air masses coming from the East and the lowest in the air masses cycled long time over Scandinavia. The total concentration of carbonyl compounds in Hyytiälä in March/April 2003 was much higher than the concentration of aromatic hydrocarbons and monoterpenes in April 2002. Scaling the concentrations against reactivity with the OH-radical showed, that in spite of relatively low ambient concentrations higher molecular weight aldehydes contribute significantly to the total OH-reactive mass of carbonyls. The impact of carbonyl compounds on OH-radical chemistry is important. Contribution of carbonyls as an OH sink is comparable to that of NO2 and higher than monoterpenes and aromatic hydrocarbons. Lifetimes of the measured carbonyls with respect to reactions with OH radicals, ozone (O3), and nitrate (NO3) radicals as well as photolysis were estimated. The main sink reactions for most of the carbonyl compounds in Hyytiälä in springtime are expected to be reactions with the OH radical and photolysis. For 6-methyl-5-hepten-2-one and limona ketone also reactions with ozone are important. The sources of carbonyl compounds are presently highly uncertain. Based on the comparisons with urban concentrations the direct anthropogenic emissions are not as important as secondary biogenic and anthropogenic sources or primary biogenic sources in Hyytiälä.

Trifluoroacetate in ocean waters.

Trifluoroacetate (TFA) is a ubiquitous xenochemical presently increasing in concentration in some environmental compartments, especially in the plant biomass of industrialized countries. Direct anthropogenic emissions of TFA are probably low, and the major anthropogenic sources are most likely various TFA precursors. As TFA has been found in ocean waters from remote locations, the question arose whether it is also a naturally occurring environmental chemical. Determination of the depth dependence of TFA in the ocean water column should shed some light on this question. However, in environmental analytical studies, the risk of systematic errors can be high and may lead to wrong conclusions. Therefore, special attention has been paid to the fact that TFA is a common atmospheric pollutant in the urban environment and that contributions from sampling, storage, and transport potentially lead to artificially high TFA values. The results of the ocean water sampling campaigns indicate that TFA is a naturally occurring chemical, homogeneously distributed in ocean waters of all ages with a concentration of about 200 ng/L.