Atmospheric Black Carbon Concentrations Research Articles

Spatiotemporal variations of atmospheric black carbon concentration and its correlation with meteorological and environmental factors in Xinjiang, China, from 2010 to 2022.

Black carbon (BC) is a pollutant produced by the combustion of fossil fuels and biomass fuels, which has a huge impact on regional climate, atmospheric environment, and human health. In this study, based on MERRA-2 reanalysis data and ground-based observation data, the Mann-Kendall (MK) test and random forest (RF) model were used to explore the spatiotemporal variation characteristics of atmospheric BC concentration in Xinjiang, China and its correlation with meteorological and environmental covariates in 2010-2022. The results showed that the use of MERRA-2 reanalysis data to explore the spatiotemporal variation characteristics of BC concentration in Xinjiang had high reliability (relative average deviation (RAD) = 0.65). From 2010 to 2022, the annual average concentration of atmospheric BC in Xinjiang was 195.40±15.55ng/m3, and the multi-year average change rate was -0.05%. The winter season had the highest atmospheric BC concentration (145.52 ± 39.31 ng/m3), followed by autumn (124.95±28.82 ng/m3), spring (74.05 ± 9.96 ng/m3), and summer (73.41 ± 5.69ng/m3). The atmospheric BC concentration had a significant spatial variation, showing two high-BC-concentration areas on the northern slope of the Tianshan Mountains (centered on Urumqi-Changji-Shihezi region) and the urban agglomeration around the Tarim Basin (centered on Kashgar). The RF model analysis showed that meteorological factors including snow depth, surface temperature, and humidity as well as environmental factors including NO2, PM10, and SO2 were the main factors affecting the BC concentration. This work is of great significance for clarifying the accumulation and spatial distribution characteristics of atmospheric BC in northwest China and the factors influencing the atmospheric BC concentration, and helps to raise public attention to the increasingly serious climate change and public health problems caused by BC.

Atmospheric aerosol optical properties and trends over Antarctica using in-situ measurements and MERRA-2 aerosol products

Columnar aerosol loading and surface level atmospheric black carbon (BC) concentration over the Antarctic are examined using the measurements carried out at the Indian Antarctic stations, Bharati and Maitri, as part of the 36th Indian Scientific Expedition (2016–17) to Antarctica (ISEA). The mean aerosol optical depth (AOD) at wavelength 500 nm at Bharati is observed to be 0.101 ± 0.01, whereas that at Maitri is 0.047 ± 0.003. Columnar aerosol loading at Bharati is found to be more than two times that measured at Maitri. The daily mean surface level atmospheric BC concentration at Bharati in the Austral summer from December 2016 to February 2017 is 24 ± 16.5 ngm−3. Comparison of this measurement with earlier reported values over the same region indicates an increase in surface-level atmospheric BC concentration. Long-term (1997–2017) trend analysis carried out using MERRA-2 aerosol reanalysis data also corroborates the increasing trend in AOD and BC concentration with 0.005 (0.007) yr−1 and 0.3 (0.27) ngm−3 yr−1 over Bharati (Maitri) respectively. Spectral variations of aerosol absorption coefficients show absorption angstrom exponent values (AAE) close to unity (1.096 ± 0.029), which indicates that fossil fuel emission is the primary source of absorbing aerosols over this region. During the study period, air mass back trajectory analysis indicates that the sources are from the Antarctic, coastal, and southern ocean regions with no long-range transport from other continents in the southern hemisphere.

Nearly five-year continuous atmospheric measurements of black carbon over a suburban area in central France

Atmospheric black carbon (BC) concentration over a nearly 5 year period (mid-2017–2021) was continuously monitored over a suburban area of Orléans city (France). Annual mean atmospheric BC concentration were 0.75 ± 0.65, 0.58 ± 0.44, 0.54 ± 0.64, 0.48 ± 0.46 and 0.50 ± 0.72 μg m−3, respectively, for the year of 2017, 2018, 2019, 2020 and 2021. Seasonal pattern was also observed with maximum concentration (0.70 ± 0.18 μg m−3) in winter and minimum concentration (0.38 ± 0.04 μg m−3) in summer. We found a different diurnal pattern between cold (winter and fall) and warm (spring and summer) seasons. Further, fossil fuel burning contributed >90 % of atmospheric BC in the summer and biomass burning had a contribution equivalent to that of the fossil fuel in the winter. Significant week days effect on BC concentrations was observed, indicating the important role of local emissions such as car exhaust in BC level at this site. The behavior of atmospheric BC level with COVID-19 lockdown was also analyzed. We found that during the lockdown in warm season (first lockdown: 27 March–10 May 2020 and third lockdown 17 March–3 May 2021) BC concentration were lower than in cold season (second lockdown: 29 October–15 December 2020), which could be mainly related to the BC emission from biomass burning for heating. This study provides a long-term BC measurement database input for air quality and climate models. The analysis of especially weekend and lockdown effect showed implications on future policymaking toward improving local and regional air quality as well.

Effects of Winter Heating on Urban Black Carbon: Characteristics, Sources and Its Correlation with Meteorological Factors

Coal combustion for winter heating is a major source of heavy atmospheric pollution in China, while its impacts on black carbon (BC) are not yet clear. A dual-spot Aethalometer was selected to monitor the atmospheric BC concentration in Zhengzhou, China, during the heating season, which is from 15 November through 15 March of the following year, and the non-heating season (days other than heating season). The characteristics and sources of BC were analyzed, and a concentration weight trajectory (CWT) analysis was conducted. The results showed that the BC concentrations in the heating season were generally higher than those in the non-heating season. The diurnal variation in BC concentrations during heating season was bimodal, and that during the non-heating season was unimodal. The α-values in the heating and non-heating seasons indicated that combustion of coal and biomass and vehicle emissions were the major BC sources for the heating season and non-heating season, respectively. BC concentrations were positively correlated with PM2.5, PM10, CO, and NOX. There was a strong negative correlation between wind speed and BC concentrations, and that for relative humidity was the opposite. BC concentration during heating season was mainly influenced by the northwestern areas of China and the eastern part of Henan, and that in the non-heating season was mainly from the northeastern areas of China and southern Henan.

Relative contributions of fossil fuel and biomass burning sources to black carbon aerosol on the Southern Atlantic Ocean Coast and King George Island (Antarctic Peninsula).

Carbonaceous aerosols can affect climate, especially particles containing black carbon (BC). BC originated from the incomplete combustion of fossil fuel and biomass, which can heat the atmosphere and increase ice melting, but little is known about BC sources to Antarctica. We quantified the contribution of distant origin (biomass burning) and local emissions (fossil fuel) to atmospheric BC concentration in the King George Island (Antarctic Peninsula) and the Southern Ocean. We examine the BC concentrations using a multi-wavelength Aethalometer AE-33 and AE-42 aboard the Brazilian Oceanographic Research Ship Almirante Maximiano. The results indicate that the region is influenced by local sources and air masses coming from surrounding continents. Fossil fuel combustion was the major source of carbonaceous aerosols in the region, whereas the total average concentration was 41.8 ± 22.8 ng m-3. The findings indicate a contribution of biomass burning coming from low and mid-latitudes of South America over the Antarctic Peninsula and the Southern Ocean around 62ºS latitude. We demonstrated that fossil fuel is the main contributor to atmospheric BC concentration for the Austral summer and autumn. Scientific stations, local tourism, and traffic are possible local BC sources. Our work invokes the urgency of questionable sustainability issues about Antarctica exploration.

A long-term analysis of atmospheric black carbon MERRA-2 concentration over China during 1980–2019

Black carbon (BC), an important component of atmospheric aerosols, has a great influence on regional and global radiation balance, climate and human health due to its small particle size, large specific surface area and radiation forcing. The long-term variation of atmospheric BC over China during 1980–2019 was investigated through MERRA-2 reanalysis data. MERRA-2 BC generally presented a good correlation (average R = 0.61) with 852 monthly samples from ground-based observations at 64 stations around China. In recent 40 years, the annual-averaged atmospheric BC concentration derived from MERRA-2 reanalysis data was 1.10 ± 0.22 μg/m3, with an average annual growth rate of 1.52%. The monthly BC concentrations showed a "U"-shaped trend. Based on the Mann-Kendall trend analysis, the BC concentration can be roughly divided into three stages: (1) the “low value” stage with slow growth rate (1.68%) (1980–1999, 0.91 ± 0.10 μg/m3), (2) the fluctuating “median value” stage with high growth rate (4.44%) (2000–2007, 1.28 ± 0.13 μg/m3), and (3) the “high value” stage with slow downtrend (−0.87%) (2008–2019, 1.32 ± 0.06 μg/m3). Peak times and multi-year average growth rates of BC concentration and emission were not synchronized. The spatial distribution, dividing by the Hu Line, a line dividing the population density and urbanization of China, formed three BC high-value areas in Sichuan Basin, Northern Henan area and Beijing-Tianjin-Hebei (BTH). The altitude where the concentration of BC increased fastest at an average annual growth rate of 3.47% during 1980–2019 was between 0 and 500 m. The growth rate of BC concentration was close to zero as the altitude increased. During the past 40 years, significant overall uptrends were detected in MERRA-2 BC concentration with Mann-Kendall trend analysis at pixel scale, especially during 1980–1999 and 2000–2007. This increasing trend was more obvious in the eastern Hu Line. Whereas, a downward trend was appeared in the plains and basins of southeast China during 2008–2019.

Changes and Potential Sources of Atmospheric Black Carbon Concentration in Shanghai over the Past 40 Years Based on MERRA-2 Reanalysis Data

As an important component of atmospheric aerosols, black carbon (BC) has a great influence on the regional and global radiation balance, climate, and human health due to its small particle size, large specific surface area, and radiative forcing potential. Here, the spatio-temporal characteristics of atmospheric BC were investigated based on modern-era retrospective analysis for research and applications version 2 (MERRA-2) reanalysis data and ground observation data during 1980-2019 in Shanghai, a highly urbanized city in mainland China. The influences of local emissions and regional transmission on regional-scale BC concentrations were examined using the M-K trend test, backward trajectory analysis, and the potential source contribution function (PSCF). The results showed that:① MERRA-2 BC and ground observation datasets showed good consistency (R∈[0.68, 0.72]), indicating that MERRA-2 reanalysis data can be used to reveal long-term changes in ground-level atmospheric BC concentrations; ② Atmospheric BC concentrations in Shanghai over the past 40 years can be divided into three stages:a "low value" stage of slow growth[1980-1986, (1.75±0.17) μg·m-3], a relatively stable "median value" stage[1987-1999, (2.18 ±0.07) μg·m-3], and a fluctuating "high value" stage[2000-2019, (3.07±0.31) μg·m-3]. Seasonally, Shanghai's BC concentrations generally show a "U" pattern with low concentrations in summer and high concentrations in winter. As a result of black carbon emissions from marine diesel engines and other engines used for water transportation, a small peak also occurs in July; ③ The diagnostic quality ratio of air pollutants and the bivariate correlation analysis[R(BC-NO2)>R(BC-CO)>R(BC-SO2)] indicated that traffic emissions were the main sources of atmospheric BC in Shanghai, especially by heavy diesel vehicles; ④ The backward trajectory and PSCF analyses found that the air mass of Shanghai in summer was dominated by a clean sea breeze, accounting for 77.18%. In contrast, during the other seasons, more than 50% of the air mass came from the north. The potential source regions of atmospheric BC in Shanghai are mainly distributed in eastern China, expanding outwards and centering on the Yangtze River Delta, and the expansion direction is consistent with the directions of the backward trajectories.

Observations of black carbon and albedo over a Central Himalayan Glacier (Satopanth): Preliminary results

Simultaneous measurements of ambient atmospheric black carbon (BC) mass concentrations and radiative fluxes were carried out over Satopanth glacier in the central Himalayas from September 22 to October 2, 2016, as a part of a glacier campaign experiment. The daily mean atmospheric BC concentrations varied between 165 ± 20–263 ± 32 ng m−3 with a mean of 199 ± 54 ng m−3 during the observational period. The measured average surface albedo was found to be 0.24 ± 0.11 during the entire period of observation. Spectral albedo from Moderate Resolution Imaging Spectroradiometer - Bidirectional Reflectance Distribution Function (MODIS-BRDF) satellite observation and net radiometer derived glacier albedo was found to be in good agreement with a correlation of 0.64 over the region. Concentration weighted trajectory analysis (CWT) over the site indicates a 70% BC transport from the Indo-Gangetic plain, Pakistan, and the Middle East region. BC radiative forcing was estimated using an optical model along with a radiative transfer model. An average BC direct radiative forcing of −5.4 ± 0.25 W m−2 and 2.4 ± 0.19 W m−2 was found respectively in the surface and at the top of the atmosphere (TOA) during the experimental period. The estimated average BC induced heating rate was found to be 0.33 ± 0.04 K day−1over the region.

Quantification and implication of measurement bias of ambient atmospheric BC concentration

Black carbon (BC) aerosols have severe impacts on climate and health. Most atmospheric BC loadings are now predominantly reported for the PM2.5 size cut-off. Based on 39 published set of ambient BC concentrations from around the world where PM2.5 and PM10 were collected in parallel, we demonstrate that BC in PM2.5 was only around 80% of that in PM10. The implication is that around 20% of BC in the global ambient atmosphere is ignored with the now-legacy PM2.5 sampling approach. Correspondingly, BC of freshly emitted particles from combustion activities is dominantly reported in terms of PM2.5, and thus inflicting a bias in the total BC emission inventories. A consequence is that ambient BC is underpredicted when derived from models based on (PM2.5) emission inventories. This consideration contributes to reconcile existing systematic offset between model predictions and observation-based estimates of climate-relevant effects of anthropogenic BC aerosols. We propose that total ambient BC concentration should be considered rather than the PM2.5 portion to reduce the uncertainties in estimates of BC effects on the climate.

Measurement of Atmospheric Black Carbon Concentration in Rural and Urban Environments: Cases of Lamto and Abidjan

Measurement of Atmospheric Black Carbon Concentration in Rural and Urban Environments: Cases of Lamto and Abidjan

Concentration of Black Carbon in the Near-Surface Atmosphere in the Pechora-Ilych Natural Reserve: Measurements and Merra-2 Reanalysis

The concentration of black carbon (BC), measured in near-surface air on the territory of the Pechora-Ilych State Natural Biosphere Reserve (PISNBR) on the western side of the Northern Ural Mountains, far from sources, is presented for two years (December 2017–November 2019). The temporal variations in BC concentration throughout a year and the location of its main sources are analyzed. The average values for two cold and two warm half-years were 128 and 62 ng/m3, respectively. The BC concentration in near-surface atmosphere was compared with MERRA-2 reanalysis data. On a monthly scale, the anomalous increase in BC concentration during short-term smoke aerosol transport across the observation area is more clearly revealed from the reanalysis data, rather than by values measured at a single point. Daily monitoring allows us to detect the specific dates of such situations.

Concentrations and Size Distributions of Black Carbon in the Surface Snow of Eastern Antarctica in 2011

AbstractKnowledge of black carbon (BC) concentrations and size distributions within surface snow in Antarctica is limited. However, these measurements are important to understanding global aerosol transport from combustion sources, and BC contributes to positive radiative forcing. This study analyzed the concentrations and size distributions of BC and inorganic ions in snow samples collected at the Syowa station in Antarctica from April to December 2011 and along a traverse route to an inland (Mizuho) station. The BC size distributions in snow were bimodal with mass median diameters of ~140 and ~690 nm. We also estimated the mass median diameter from unimodal distributions and found smaller diameters than were reported by other studies. The mass concentrations of BC in snow were higher in inland samples than in Syowa samples. Among Syowa samples, the BC concentrations in December (2117.3 ng L−1 on average) were higher than in other periods (288.2 ng L−1 on average). The December samples experienced ambient temperatures above 0 °C, and the atmospheric BC concentrations did not increase simultaneously. Inorganic ions originated from the ocean and decreased with increasing distance from the coastal area. We conclude that the BC concentrations in surface snow increased mainly by postdeposition processes through the loss of water mass due to melting, evaporation, and sublimation. Our study is the first to report detailed BC concentrations and size distributions in eastern Antarctica, and the results will help to evaluate BC global transport, the snow albedo estimations in this region, and the climate impacts of BC.

Atmospheric black carbon concentrations in Mexico

Atmospheric black carbon concentrations were measured at two urban sites (Mexico City and Monterrey), one suburban site (Juriquilla) and one high-altitude site (Altzomoni) in Mexico during 2015 and part of 2016. Black carbon concentrations were compared against other criteria gases finding a strong correlation with carbon monoxide at the urban sites. The carbon monoxide-black carbon correlation for the Mexico City site is 0.77. Urban sites had an average black carbon concentration of above 2.5 μg m−3, the suburban site 0.75 μg m−3, and the high-altitude site 0.27 μg m−3. Compared to other studies, the average levels are comparable, and the urban and suburban locations showed a trend towards increased atmospheric black carbon concentrations at year end. Other urban places (Guadalajara, Cuernavaca, and Iztapalapa) reported black carbon concentrations, but for less than a year. For the first time, a Latin-American country (Mexico) measured black carbon continuously at several sites for a year applying the same data quality assurance.

Seasonal Variability of Atmospheric Aerosols in Karachi, Pakistan

A variety of in situ and satellite-derived data of aerosols like atmospheric black carbon concentrations wereused to probe the seasonal differences of aerosol concentration in Karachi, Pakistan for one year. Daily [black carbon]varied from about 4000 to 50,000 ng/m3 with the mean maximum of 14700 ng/m3 in February, primarily duringmornings and evenings. The [black carbon] concentrations were at a maximum during winter months of November toFebruary i.e. around 12000 ng/m3 and were at minimum value during summer from June to September (3000 ng/m3).Short term and long-term variabilities were mostly affected by meteorological parameters. Apart from industrial andindiscriminate solid waste burning, most important source of BC emissions in Karachi was vehicular traffic, since overa million vehicles were registered in the city. Aerosol Optical Depth (AOD) from multi-band AOD, AERONET, andMODIS satellites showed a similar trend of its concentrations similar to BC. Aeronet 500 nm AODs were at amaximum for July (0.95 monsoons) and minimum (around 0.4) in November-February. Seasonal variation of AOD(Aeronet) was matching at other wavelengths, while the deviation in the spectral dependency of AOD was uncertain. Itimplied that a columnar spectral optical depth represented different aerosol type association having advection fromvarious directions and sources. Relevant stakeholders should play their role to reduce BC emissions to mitigate illhealth impacts in this metropolitan city.

Seasonal Variability of Atmospheric Aerosols in Karachi, Pakistan

A variety of in situ and satellite-derived data of aerosols like atmospheric black carbon concentrations wereused to probe the seasonal differences of aerosol concentration in Karachi, Pakistan for one year. Daily [black carbon]varied from about 4000 to 50,000 ng/m3 with the mean maximum of 14700 ng/m3 in February, primarily duringmornings and evenings. The [black carbon] concentrations were at a maximum during winter months of November toFebruary i.e. around 12000 ng/m3 and were at minimum value during summer from June to September (3000 ng/m3).Short term and long-term variabilities were mostly affected by meteorological parameters. Apart from industrial andindiscriminate solid waste burning, most important source of BC emissions in Karachi was vehicular traffic, since overa million vehicles were registered in the city. Aerosol Optical Depth (AOD) from multi-band AOD, AERONET, andMODIS satellites showed a similar trend of its concentrations similar to BC. Aeronet 500 nm AODs were at amaximum for July (0.95 monsoons) and minimum (around 0.4) in November-February. Seasonal variation of AOD(Aeronet) was matching at other wavelengths, while the deviation in the spectral dependency of AOD was uncertain. Itimplied that a columnar spectral optical depth represented different aerosol type association having advection fromvarious directions and sources. Relevant stakeholders should play their role to reduce BC emissions to mitigate illhealth impacts in this metropolitan city.

Global radiative effects of solid fuel cookstove aerosol emissions

Abstract. We apply the NCAR CAM5-Chem global aerosol-climate model to quantify the net global radiative effects of black and organic carbon aerosols from global and Indian solid fuel cookstove emissions for the year 2010. Our assessment accounts for the direct radiative effects, changes to cloud albedo and lifetime (aerosol indirect effect, AIE), impacts on clouds via the vertical temperature profile (semi-direct effect, SDE) and changes in the surface albedo of snow and ice (surface albedo effect). In addition, we provide the first estimate of household solid fuel black carbon emission effects on ice clouds. Anthropogenic emissions are from the IIASA GAINS ECLIPSE V5a inventory. A global dataset of black carbon (BC) and organic aerosol (OA) measurements from surface sites and aerosol optical depth (AOD) from AERONET is used to evaluate the model skill. Compared with observations, the model successfully reproduces the spatial patterns of atmospheric BC and OA concentrations, and agrees with measurements to within a factor of 2. Globally, the simulated AOD agrees well with observations, with a normalized mean bias close to zero. However, the model tends to underestimate AOD over India and China by ∼ 19 ± 4 % but overestimate it over Africa by ∼ 25 ± 11 % (± represents modeled temporal standard deviations for n = 5 run years). Without BC serving as ice nuclei (IN), global and Indian solid fuel cookstove aerosol emissions have net global cooling radiative effects of −141 ± 4 mW m−2 and −12 ± 4 mW m−2, respectively (± represents modeled temporal standard deviations for n = 5 run years). The net radiative impacts are dominated by the AIE and SDE mechanisms, which originate from enhanced cloud condensation nuclei concentrations for the formation of liquid and mixed-phase clouds, and a suppression of convective transport of water vapor from the lower troposphere to the upper troposphere/lower stratosphere that in turn leads to reduced ice cloud formation. When BC is allowed to behave as a source of IN, the net global radiative impacts of the global and Indian solid fuel cookstove emissions range from −275 to +154 mW m−2 and −33 to +24 mW m−2, with globally averaged values of −59 ± 215 and 0.3 ± 29 mW m−2, respectively. Here, the uncertainty range is based on sensitivity simulations that alter the maximum freezing efficiency of BC across a plausible range: 0.01, 0.05 and 0.1. BC–ice cloud interactions lead to substantial increases in high cloud (< 500 hPa) fractions. Thus, the net sign of the impacts of carbonaceous aerosols from solid fuel cookstoves on global climate (warming or cooling) remains ambiguous until improved constraints on BC interactions with mixed-phase and ice clouds are available.

Trends of atmospheric black carbon concentration over the United Kingdom

The continuous observations over a period of 7 years (2009–2016) available at 7 locations show declining trend of atmospheric BC in the UK. Among all the locations, the highest decrease of 8 ± 3 percent per year was observed at the Marylebone road in London. The detailed analysis performed at 21 locations during 2009–2011 shows that average annual mean atmospheric BC concentration were 0.45 ± 0.10, 1.47 ± 0.58, 1.34 ± 0.31, 1.83 ± 0.46 and 9.72 ± 0.78 μgm−3 at rural, suburban, urban background, urban centre and kerbside sites respectively. Around 1 μgm−3 of atmospheric BC could be attributed to urban emission, whereas traffic contributed up to 8 μg m−3 of atmospheric BC near busy roads. Seasonal pattern was also observed at all locations except rural and kerbside location, with maximum concentrations (1.2–4 μgm−3) in winter. Further, minimum concentrations (0.3–1.2 μgm−3) were observed in summer and similar concentrations in spring and fall. At suburban and urban background locations, similar diurnal pattern were observed with atmospheric BC concentration peaks (≈1.8 μg m−3) in the morning (around 9 a.m.) and evening (7–9 p.m.) rush hours, whereas minimum concentrations were during late night hours (peak at 5 a.m.) and the afternoon hours (peak at 2 p.m.). The urban centre values show a similar morning pattern (peak at 9 a.m.; concentration - 2.5 μgm−3) in relation to background locations but only a slight decrease in concentration in the afternoon which remained above 2 μgm−3 till midnight. It is concluded that the higher flow of traffic at urban centre locations results in higher atmospheric BC concentrations throughout the day. Comparison of weekday and weekend daily averaged atmospheric BC showed maximum concentrations on Friday, having minimum levels on Sunday. This study will help to refine the atmospheric BC emission inventories and provide data for air pollution and climate change models evaluation, which are used to formulate air pollution mitigation policies.

Impacts of absorbing aerosol deposition on snowpack and hydrologic cycle in the Rocky Mountain region based on variable-resolution CESM (VR-CESM) simulations

Abstract. The deposition of light-absorbing aerosols (LAAs), such as black carbon (BC) and dust, onto snow cover has been suggested to reduce the snow albedo and modulate the snowpack and consequent hydrologic cycle. In this study we use the variable-resolution Community Earth System Model (VR-CESM) with a regionally refined high-resolution (0.125°) grid to quantify the impacts of LAAs in snow in the Rocky Mountain region during the period 1981–2005. We first evaluate the model simulation of LAA concentrations both near the surface and in snow and then investigate the snowpack and runoff changes induced by LAAs in snow. The model simulates similar magnitudes of near-surface atmospheric dust concentrations as observations in the Rocky Mountain region. Although the model underestimates near-surface atmospheric BC concentrations, the model overestimates BC-in-snow concentrations by 35 % on average. The regional mean surface radiative effect (SRE) due to LAAs in snow reaches up to 0.6–1.7 W m−2 in spring, and dust contributes to about 21–42 % of total SRE. Due to positive snow albedo feedbacks induced by the LAA SRE, snow water equivalent is reduced by 2–50 mm and snow cover fraction by 5–20 % in the two regions around the mountains (eastern Snake River Plain and southwestern Wyoming), corresponding to an increase in surface air temperature by 0.9–1.1 °C. During the snow melting period, LAAs accelerate the hydrologic cycle with monthly runoff increases of 0.15–1.00 mm day−1 in April–May and reductions of 0.04–0.18 mm day−1 in June–July in the mountainous regions. Of all the mountainous regions, the Southern Rockies experience the largest reduction of total runoff by 15 % during the later stage of snowmelt (i.e., June and July). Compared to previous studies based on field observations, our estimation of dust-induced SRE is generally 1 order of magnitude smaller in the Southern Rockies, which is ascribed to the omission of larger dust particles (with the diameter > 10 µm) in the model. This calls for the inclusion of larger dust particles in the model to reduce the discrepancies. Overall these results highlight the potentially important role of LAA interactions with snowpack and the subsequent impacts on the hydrologic cycles across the Rocky Mountains.

Temporal variation and source identification of black carbon at Lin’an and Longfengshan regional background stations in China

Black carbon (BC) is a component of fine particulate matter (PM2.5), associated with climate, weather, air quality, and people’s health. However, studies on temporal variation of atmospheric BC concentration at background stations in China and its source area identification are lacking. In this paper, we use 2-yr BC observations from two background stations, Lin’an (LAN) and Longfengshan (LFS), to perform the investigation. The results show that the mean diurnal variation of BC has two significant peaks at LAN while different characteristics are found in the BC variation at LFS, which are probably caused by the difference in emission source contributions. Seasonal variation of monthly BC shows double peaks at LAN but a single peak at LFS. The annual mean concentrations of BC at LAN and LFS decrease by 1.63 and 0.26 μg m–3 from 2009 to 2010, respectively. The annual background concentration of BC at LAN is twice higher than that at LFS. The major source of the LAN BC is industrial emission while the source of the LFS BC is residential emission. Based on transport climatology on a 7-day timescale, LAN and LFS stations are sensitive to surface emissions respectively in belt or approximately circular area, which are dominated by summer monsoon or colder land air flows in Northwest China. In addition, we statistically analyze the BC source regions by using BC observation and FLEXible PARTicle dispersion model (FLEXPART) simulation. In summer, the source regions of BC are distributed in the northwest and south of LAN and the southwest of LFS. Low BC concentration is closely related to air mass from the sea. In winter, the source regions of BC are concentrated in the west and south of LAN and the northeast of the threshold area of stot at LFS. The cold air mass in the northwest plays an important role in the purification of atmospheric BC. On a yearly scale, sources of BC are approximately from five provinces in the northwest/southeast of LAN and the west of LFS. These findings are helpful in reducing BC emission and controlling air pollution.

Do contemporary (1980–2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard?

Abstract. The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. Furthermore, according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.