Surface Black Carbon Concentrations Research Articles

On the Biases of MERRA-2 Reanalysis and Ground-Based Measurements of Black Carbon Aerosols Over India

The precise measurement of black carbon (BC) and assessment of involved biases are very important considering its serious health and climatic effects. MERRA-2 reanalysis data (modern-era retrospective analysis for research and applications, version 2) of surface black carbon (SBC) and ground measurements by optical photometers (mostly Aethalometer) have been used widely to study the temporal and spatial variation of BC aerosols over India. However, a significant bias (more than 70%) between MERRA-2 SBC concentration and ground measurements of BC (by Aethalometer, referred as MBC (AE)) was observed by Malik and Aggarwal, (2021). In the current study, the possible reasons for this bias are further evaluated by comparing the MERRA-2 SBC and Aethalometer measurements against a reference photometer, i.e., continuous soot monitoring system (COSMOS). Three-year (2020-2022) SBC concentrations of MERRA-2 reanalysis data are compared against simultaneous measurements of BC by COSMOS (MBC (COSMOS)). Additionally, the biases in ground measurements are further investigated by comparing one-month (March 2023) observations of Aethalometer (MBC (AE)). These comparison results revealed a 40% underestimation in MERRA-2 reanalysis during 2020-2022. The higher underestimation (50%) of SBC during increased biomass emissions months (October to May), in contrast to the 25% underestimation during conventional emissions months (June to September), emphasizes the underestimation of biomass emissions inputs in MERRA-2 SBC reanalysis. The initial large bias between raw data of Aethalometer (MBC (AE-raw) = 1.92-1.98 times MBC (COSMOS)) get reduced significantly when correction due to multiple scattering in the filter media and mass absorption cross-section (MAC) are incorporated to correct the Aethalometer data (MBC (AE-corr) = 1.15-1.18 times MBC (COSMOS)). The findings of this study underscore the need to harmonize the correction methods for multiple scattering and redefine the MAC values for Aethalometer measurements as well as updating the anthropogenic emission inventories in MERRA-2 SBC reanalysis.

Significance of anthropogenic black carbon in modulating atmospheric and cloud properties through aerosol-radiation interaction during a winter-time fog-haze

The present study investigated the aerosol-radiation-cloud interaction of anthropogenic black carbon (BC) during a severe fog-haze event by utilizing WRF-Chem, multi-satellite and in-situ observations, reanalyses datasets, and HYSPLIT model. The WRF-Chem model adequately captured the regional distribution of aerosol, cloud, and meteorological variables over the study domain. The maximum BC surface concentration (≥7 μg m−3) was predominantly evident over densely populated central and lower Indo-Gangetic Plain (IGP) regions. Although smoke aerosols usually persisted within 4 km above the surface at daylight hours, they reached as high as 6 km during nighttime, specifically over the central IGP regions. The heavily influenced areas by BC aerosols expanded to almost the entire landmass and the continental outflow region upon doubling the anthropogenic emission. The geographical distribution of maximum perturbations in net shortwave radiation flux at the surface closely matched the spatial patterns of the highest BC concentration, indicating a crucial role of BC in directly preventing the incoming sunlight from reaching the surface. Consequently, the reduced solar radiation at the ground might result in substantial surface cooling (between −0.3 and −0.5 °C), eventually prohibiting surface evapotranspiration and diminishing the outgoing sensible and latent heat fluxes. Also, more amplified cooling in the polluted atmosphere can prevent further development of the planetary boundary layer (PBL), increasing particle entrapment near the surface via an ‘aerosol-radiation-PBL’ feedback loop. However, the most striking contrast between the two scenarios (typical and polluted) was the prolonged and intensified warming (0.5–0.8 °C) in the mid-troposphere, causing a remarkable drop in moisture (more than two to three times) and hence burn-off of liquid cloud droplets due to the semi-direct effect of increased BC aerosols. The intense mid-tropospheric heating could remarkably enhance the updraft velocity, supporting the vertical transport of the additional moisture to higher altitudes, forming more ice clouds at night. Therefore, the current study highlighted the urgency of mitigating anthropogenic BC emissions in highly polluted regions since increased emissions could considerably worsen severe fog-haze conditions and influence both liquid water and ice clouds, depending on the atmospheric conditions.

Weakened black carbon trans-boundary transport to the Tibetan Plateau during the COVID-19 pandemic

The lockdowns implemented during the coronavirus disease 2019 (COVID-19) pandemic provide a unique opportunity to investigate the impact of emission sources and meteorological conditions on the trans-boundary transportation of black carbon (BC) aerosols to the Tibetan Plateau (TP). In this study, we conducted an integrative analysis, including in-situ observational data, reanalysis datasets, and numerical simulations, and found a significant reduction in the trans-boundary transport of BC to the TP during the 2020 pre-monsoon season as a result of the lockdowns and restrictive measures. Specifically, we observed a decrease of 0.0211 μgm−3 in surface BC concentration over the TP compared to the 2016 pre-monsoon period. Of this reduction, approximately 6.04 % can be attributed to the decrease in emissions during the COVID-19 pandemic, surpassing the 4.47 % decrease caused by changes in meteorological conditions. Additionally, the emission reductions have weakened the trans-boundary transport of South Asia BC to the TP by 0.0179 μgm−2s−1; indicating that the recurring spring atmospheric pollution from South Asia to the TP will be alleviated through the reduction of anthropogenic emissions. Moreover, it is important to note that BC deposition on glaciers contributes significantly to glacier melting due to its enrichment, posing a threat to the water sustainability of the TP. Therefore, urgent measures are needed to reduce emissions from adjacent regions to preserve the TP as the “Asian Water Tower.”

Aerosol–meteorology feedback diminishes the transboundary transport of black carbon into the Tibetan Plateau

Abstract. Black carbon (BC) exerts potential effects on climate, especially in the Tibetan Plateau (TP), where the cryosphere and environment are very sensitive to climate change. The TP saw a record-breaking aerosol pollution event during the period from 20 April to 10 May 2016. This paper investigates the meteorological causes of the severe aerosol pollution event, the transboundary transport flux of BC, the aerosol–meteorology feedback, and its effect on the transboundary transport flux of BC during the severe aerosol pollution event using observational and reanalysis datasets as well as simulation based on a coupled meteorology and aerosol/chemistry model, Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). By analyzing weather maps derived from the reanalysis dataset, it is found that the plateau vortex and southerly winds were key factors that contributed to the severe aerosol pollution event. Subsequently, due to the good performance of the WRF-Chem model for the spatiotemporal characteristics of meteorological conditions and aerosols, the transboundary transport flux of BC during the pollution event was investigated. The results show that the vertically integrated cross-Himalayan transport flux of BC decreases from west to east, with the largest transport flux of 20.8 mg m−2 s−1 occurring at the deepest mountain valley in southwestern TP. Results from simulations with and without aerosol–meteorology feedback show that aerosols induce significant changes in meteorological conditions in the southern TP and the Indo-Gangetic Plain (IGP), with the atmospheric stratification being more stable and the planetary boundary layer height decreasing in both regions, and the 10 m wind speed increasing in the southern TP but decreasing in the IGP. Changes in meteorological conditions in turn lead to a decrease in the surface BC concentration in the southern TP of up to 0.16 µg m−3 (50 %) and an increase in the surface BC concentration in the IGP of up to 2.2 µg m−3 (75 %). In addition, it is found that the aerosol–meteorology feedback decreases the vertically integrated transboundary transport flux of BC from the central and western Himalayas towards the TP. This study not only provides crucial policy implications for mitigating glacier melt caused by aerosols over the TP but is also of great significance for the protection of the ecological environment of the TP.

Improving BC Mixing State and CCN Activity Representation With Machine Learning in the Community Atmosphere Model Version 6 (CAM6)

AbstractRepresenting mixing state of black carbon (BC) is challenging for global climate models (GCMs). The Community Atmosphere Model version 6 (CAM6) with the four‐mode version of the Modal Aerosol Module (MAM4) represents aerosols as fully internal mixtures with uniform composition within each aerosol mode, resulting in high degree of internal mixing of BC with non‐BC species and large mass ratio of coating to BC (RBC, the mass ratio of non‐BC species to BC in BC‐containing particles). To improve BC mixing state representation, we coupled a machine learning (ML) model of BC mixing state index trained on particle‐resolved simulations to the CAM6 with MAM4 (MAM4‐ML). In MAM4‐ML, we use RBC to partition accumulation mode particles into two new modes, BC‐free particles and BC‐containing particles. We adjust RBC to make the modeled BC mixing state index (χmode) match the one predicted by the ML model (χML). On a global average, the mass fraction of BC‐containing particles in accumulation mode decreases from 100% (MAM4‐default) to 48% (MAM4‐ML). The globally averaged χmode decreases from 78% (MAM4‐default) to 63% (MAM4‐ML, 19% reduction) and agrees well with χML (66%). The RBC decreases by 52% for accumulation mode and better agrees with observations. The hygroscopicity drops by 9% for BC‐containing particles in accumulation mode, leading to a 20% reduction in the BC activation fraction. The surface BC concentration increases most (6.9%) in the Arctic, and the BC burden increases by 4%, globally. Our study highlights the application of the ML model for improving key aerosol processes in GCMs.

Implementing and Improving CBMZ-MAM3 Chemistry and Aerosol Modules in the Regional Climate Model WRF-CAM5: An Evaluation over the Western US and Eastern North Pacific

The representation of aerosols in climate–chemistry models is important for air quality and climate change research, but it can require significant computational resources. The objective of this study was to improve the representation of aerosols in climate–chemistry models, specifically in the carbon bond mechanism, version Z (CBMZ), and modal aerosol modules with three lognormal modes (MAM3) in the WRF-CAM5 model. The study aimed to enhance the model’s chemistry capabilities by incorporating biomass burning emissions, establishing a conversion mechanism between volatile organic compounds (VOCs) and secondary organic carbons (SOCs), and evaluating its performance against observational benchmarks. The results of the study demonstrated the effectiveness of the enhanced chemistry capabilities in the WRF-CAM5 model. Six simulations were conducted over the western U.S. and northeastern Pacific region, comparing the model’s performance with observational benchmarks such as reanalysis, ground-based, and satellite data. The findings revealed a significant reduction in root-mean-square errors (RMSE) for surface concentrations of black carbon (BC) and organic carbon (OC). Specifically, the model exhibited a 31% reduction in RMSE for BC concentrations and a 58% reduction in RMSE for OC concentrations. These outcomes underscored the importance of accurate aerosol representation in climate–chemistry models and emphasized the potential for improving simulation accuracy and reducing errors through the incorporation of enhanced chemistry modules in such models.

Seasonal transition of Black carbon aerosols over Qinghai-Tibet Plateau: Simulations with WRF-Chem

Black carbon (BC) particles over the Qinghai-Tibet Plateau (Q-TP), whether suspended in the air or deposited on snow, can affect snow melt and accelerate glacier retreat. Since BC over the Q-TP may originate from different regions, it is necessary to understand the transport mechanism of BC and then provide concentrations and spatial-temporal distributions of BC over Q-TP, in order to study its radiative and climatic effects. In this study, Weather Research and Forecasting model with Chemistry (WRF-Chem), with MIX emission inventory (a mosaic Asian anthropogenic emission inventory for the MICS-Asia and the HTAP projects), was used to study the BC transport from South Asia, one of the major BC source regions, to Q-TP in April (pre-monsoon season), July (summer monsoon season) and December (winter monsoon season). The model's ability to simulate the BC transport from South Asia to the Q-TP was firstly evaluate using various reanalysis data, including 2 m temperature, precipitation, 10 m wind speed and direction and BC concentration at surface. The simulated meteorological fields and seasonal distribution and variation of BC are generally in good agreement with reanalysis data. The model showed good performance in simulating transport of BC as well. Our study showed that during pre-monsoon season, BC aerosols accumulated in the foothills of the Himalayas and were transported to southern Q-TP and even Southeast Asia via dry and wet deposition and westerly winds below 200hpa. Although the cyclonic airflow, which was favorable to transport, prevailed in South Asia, slight BC aerosols would be transported to Q-TP through wet deposition due to the efficient wet scavenging by abundant precipitation during summer monsoon season. During winter monsoon season, the prevailing westerly winds at 500hpa would transport BC aerosols from South Asia to Q-TP by dry deposition. A sensitivity simulation using PKU emission inventory (Peking University's global BC emission inventory) was then conducted to investigate the impact of different emission inventory on the modeling results. It is shown that the simulations using the different BC emission inventories overall did not have significant impacts on spatial distributions of surface concentration and column burden during three studies seasons. However, the simulated BC concentrations and burden based on PKU were overall higher than that based on MIX, that is, main differences were found in the southern part of Q-TP (i.e. adjacent to South Asia), especially during pre-monsoon and winter monsoon seasons. The differences of mean BC surface concentration ranging from 0.1 to 1 μg/m3, and burden ranging from 0.1 to 1 mg/m2 due to both higher dry and wet deposition (0.1–2 μg/m2/s for dry deposition flux, and 0.1–3 μg/m2/s for wet deposition flux) during pre-monsoon. During winter monsoon seasons, relatively large differences (0–3 μg/m3 for concentration, and 0–2 mg/m2 for burden, and 0.1–3 μg/m2/s for dry deposition flux) were found in southern Q-TP.

Mutual response hypothesis between surface temperature and aerosol (BC and non-BC) mass concentration observed in an urban environment

The mutual response between near surface aerosol concentration and surface temperature works in a complicated manner. A recent study has introduced a hypothesis of mutual response between surface temperature and near surface black carbon (BC) mass concentration which states that ‘more fall in morning hour surface temperature (T) contribute to the enhancement of BC fumigation peak after the sunrise which positively impacts the extra rise in mid-day temperature over a region during the day time’. Morning hour surface temperature is proportionally linked with the strength of the night time near surface temperature inversion which contributes to the enhancement of the fumigation peak of BC aerosols after the sunrise and the enhanced fumigation peak can impact the degree of the mid-day surface temperature rise by influencing the instantaneous heating. However, it didn't mention the role of non-BC aerosols. Further, the hypothesis was drawn based on the co-located ground-based observations of surface temperature and BC concentration at a rural location of peninsular India. Though, it was mentioned that the hypothesis can be tested independently of locations, but was not thoroughly validated for an urban environment where the loading of both BC and non-BC aerosols are high. In this context, the first objective of the present work is to methodically test the BC –T hypothesis over an Indian metropolitan city, Kolkata, using the suite of measurements obtained from Kolkata Camp Observatory of NARL (KCON) along with other supporting data. In addition, the validity of the hypothesis for the non-BC fraction of PM2.5 aerosols over the same location is also tested. Besides ascertaining the above-mentioned hypothesis over an urban location, it is found that the enhancement of non-BC PM2.5 aerosols peak after the sunrise can negatively influences the mid-day temperature rise over a region during the day time.

Evaluating BC Aging Processes in the Community Atmosphere Model Version 6 (CAM6)

AbstractThe uncertainty of the climatic effect of Black carbon (BC) remains large. One critical uncertainty source that needs to be captured is BC aging. Here we use the Community Atmosphere Model version 6 (CAM6) configured with the four‐mode version of the Modal Aerosol Module (MAM4) to evaluate the modeled BC aging process with recent laboratory and in‐situ measurements over China. As revealed by the comparison of BC aging timescale and number fraction of aged BC against recent measurements, the modeled condensation aging timescale is estimated to be about 0.8 hr (17%) faster than the chamber measurement, and the diurnal variations of modeled BC aging degree are typically higher than observations mainly due to the fast increase in modeled BC aging degree during daytime. Further analysis shows that the condensation aging dominates (>70%) BC aging across China. More specifically, the condensation of secondary organic aerosol (SOA) vapor contributes most to BC aging over China. Slowing down BC aging increases the modeled surface BC concentration over remote Western China and BC burden, but hardly changes surface BC concentration over Eastern China. Our results suggest that BC aging representation in the MAM4 needs to be further improved toward slowing down the BC aging rate, especially the condensation aging by SOA, to improve the BC simulation over remote areas and its impact on BC transport in MAM4.

Impacts of springtime biomass burning in Southeast Asia on atmospheric carbonaceous components over the Beibu Gulf in China: Insights from aircraft observations.

Limited by the scarcity of in situ vertical observation data, the influences of biomass burning in Southeast Asia on major atmospheric carbonaceous compositions in downwind regions have not been thoroughly studied. In this study, aircraft observations were performed to obtain high time-resolved in situ vertical distributions of black carbon (BC) as well as carbon monoxide (CO) and carbon dioxide (CO2). Four types of profiles were revealed: Mode I (from 2000 to 3000 m, the BC, CO and CO2 concentrations were enhanced), Mode II (with increasing altitude, the BC, CO and CO2 concentrations almost decreased), Mode III (inhomogeneous vertical BC, CO and CO2 profiles with BC peaks were observed from 2500 to 3000 m) and Mode IV (the BC, CO and CO2 concentrations increased above 1500 m). Furthermore, simulations were conducted to calculate radiative forcing (RF) caused by BC and study the heating rate (HR) of BC in combination with the vertical BC profiles. A larger BC distribution in the atmosphere resulted in a sharp RF change from negative to positive values, imposing a nonnegligible influence on the atmospheric temperature profile, with maximum HR values ranging from 0.4 to 5.8 K/day. The values of the absorption Ångström exponent (AAE) were 1.46 ± 0.11 and 1.48 ± 0.17 at altitudes from 1000 to 2000 and 2000-3000 m, respectively. The average BC light absorption coefficient at the 370 nm wavelength (α BC (370)) accounted for 50.3 %-76.8 % of the α (370), while the brown carbon (BrC) light absorption coefficient at the 370 nm wavelength (α BrC (370)) contributed 23.2 %-49.7 % to the α (370) at altitudes of 1000-2000 m. At altitudes of 2000-3000 m, α BC (370) and α BrC (370) contributed 43.8 %-88.2 % and 11.8 %-56.2 % to the α (370), respectively. These findings show that calculations that consider the surface BC concentration but ignore the vertical BC distribution could result in massive uncertainties in estimating the RF and HR caused by BC. This study helped achieve a deeper understanding of the influences of biomass burning over the region of Southeast Asia on the profiles of atmospheric carbonaceous compositions and atmospheric BC absorption and its warming effect.

Spatial distribution and temporal variation of biomass burning and surface black carbon concentrations during summer (2015‒2021) in India.

Historical biomass burning in summer season (April‒June, during 2015‒2021) was assessed by studying active fire spot data recorded by the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard NASA/NOAASuomi NPP satellite and mapping the same over Indian landmass. The fire spots often formed regional clusters and most profusely covered the states of Odisha, Chhattisgarh, Andhra Pradesh, Telengana, Madhya Pradesh, Maharashtra, Jharkhand, Karnataka, Punjab, Uttar Pradesh, Haryana, Gujarat, Tamil Nadu, Manipur, Nagaland, and Mizoram during April but their number decreased conspicuously in May and further in June. Forward movements of air masses potentially carrying fire-induced air pollutants from five principal fire cluster regions (northern, south eastern, western, north-eastern, and central) of India during April and May in2021 were traced by 6-day forward airtrajectory modelling. It was observed that many parts of India were the recipients of air coming from the above principal fire clusters. In each year, the surface mass concentration of black carbon (BC), one of the most prominent markers of biomass burning, was higher in April over May and June in the affected regions, commensurate with the most active period of fire. The BC surface mass concentrations progressively declined thereafter in May and June with decreasing number of active fire spots along with declining average monthly height of the planetary boundary layer (PBL), indicating integral connection of surface BC levels with biomass burning. The study suggests that in spite of more favourable meteorological conditions in summer, extensivebiomass burning may have hada crucial role to play in perturbing local and regional air quality over India by generatingBC and other air pollutants.

Meteorological Influences on Anthropogenic PM2.5 in Future Climates: Species Level Analysis in the Community Earth System Model v2

AbstractBiomass and fossil fuel burning impact air quality by injecting fine particulate matter (PM2.5) and its precursors into the atmosphere, which poses serious threats to human health. However, the surface concentration of PM2.5 depends not only on the magnitude of emissions, but also secondary production, transport, and removal. For example, in response to greenhouse gas driven warming, meteorological conditions that govern aerosol removal, primarily through rainfall and wet deposition, could shift in pattern, frequency, and intensity. This climate change driven process can impact air quality even without changes in aerosol emissions. In this experiment, we conduct new simulations by fixing aerosol emissions at present‐day levels in the Community Earth System Model Version 2, but increasing greenhouse gases through the 21st century. In our results, the changes in patterns and intensity of PM2.5 are found to be associated with precipitation (via aerosol removal), temperature (via secondary organic aerosol (SOA) formation), and moisture and clouds (via sulfate production). A decrease in wet day frequency (∼1.2% global mean) contributes to increases in the surface concentrations of black carbon, primary organic matter, and sulfate in many regions. This is offset in some regions by an upward vertical shift in the level where SOA forms, which contributes to higher column burden but lower surface concentration. These results highlight a need, using a variety of modeling tools, to continually reassess aerosol emissions regulations in response to anticipated climate changes.

Impact of the initial hydrophilic ratio on black carbon aerosols in the Arctic

Black carbon (BC) contributes to patterns of Arctic warming, yet the initial hydrophilic ratio (IHR) of BC emitted from various sources and its impact on Arctic BC remain uncertain. With the use of a tagged tracer method of BC implemented in the global chemistry transport model GEOS-Chem, IHRs were partitioned into 7 BC combustion source categories according to the PKU-BC-v2 emission inventory. The results show that as the IHR increased, the concentration of BC decreased globally. The impact on Arctic BC was mainly reflected in the vertical profile and the burden rather than at the surface. Specifically, the greatest impact of IHR on Arctic BC appeared in summer, with the largest perturbation appearing at an altitude of approximately 600 hPa, reaching 8%. This change in BC vertical profile was mainly caused by the IHR change of wildfire combustion in Russia (44%) and Canada (51%), and the emissions from these two regions were also the two most important contributors to the BC concentration and burden in the middle and lower Arctic atmosphere in summer. In the other three seasons, anthropogenic combustion sources (oil, coal, and biomass) in East Asia, Russia, and Europe accounted for 19–40%, 14–28%, and 7–23%, respectively, of the monthly BC burden. Emissions from Russia were the most important contributor (27–43%) to the monthly BC surface concentration. Due to the large adjustment in IHR from 20% to 70%, biomass burning in Europe was shown to be the dominant contributor causing both burden (39%) and surface concentration (88%) changes in all seasons except summer.

Contribution of South Asian biomass burning to black carbon over the Tibetan Plateau and its climatic impact.

This study used a regional climate-chemistry transport model, WRF-Chem v3.9.1, to evaluate the impact of South Asian biomass burning on black carbon (BC) over the Tibetan Plateau (TP) and its climatic effects for an entire year. The simulation, which was validated by comparing surface meteorological parameters and BC concentration against in-situ observations over South Asia and the TP, provided a perspective on the seasonal variations and regional spatial patterns of BC concentration. Using a sensitivity simulation where BC emissions from biomass burning were removed from South Asia, this study found South Asian biomass burning emissions contributed up to 90% of BC mass over the TP during the pre-monsoon season, specifically emissions from western India for the simulated year. The emissions led to reduced surface radiative forcing, causing the temperature to decrease accordingly. However, column cloud water was increased. This study suggested that the biomass burning emissions from South Asia have significant impact on atmospheric BC over the TP, especially during the pre-monsoon season. Therefore, reducing biomass burning emissions from South Asia is potentially important for alleviating the effects of BC on climatic and environmental conditions over the TP and surrounding regions.

Estimation of Surface Concentrations of Black Carbon from Long-Term Measurements at Aeronet Sites over Korea

We estimated fine-mode black carbon (BC) concentrations at the surface using AERONET data from five AERONET sites in Korea, representing urban, rural, and background. We first obtained the columnar BC concentrations by separating the refractive index (RI) for fine-mode aerosols from AERONET data and minimizing the difference between separated RIs and calculated RIs using a mixing rule that can represent a real aerosol mixture (Maxwell Garnett for water-insoluble components and volume average for water-soluble components). Next, we acquired the surface BC concentrations by establishing a multiple linear regression (MLR) between in-situ BC concentrations from co-located or adjacent measurement sites, and columnar BC concentrations, by linearly adding meteorological parameters, month, and land-use type as the independent variables. The columnar BC concentrations estimated from AERONET data using a mixing rule well reproduced site-specific monthly variations of the in-situ measurement data, such as increases due to heating and/or biomass burning and long-range transport associated with prevailing westerlies in the spring and winter, and decreases due to wet scavenging in the summer. The MLR model exhibited a better correlation between measured and predicted BC concentrations than those based on columnar concentrations only, with a correlation coefficient of 0.64. The performance of our MLR model for BC was comparable to that reported in previous studies on the relationship between aerosol optical depth and particulate matter concentration in Korea. This study suggests that the MLR model with properly selected parameters is useful for estimating the surface BC concentration from AERONET data during the daytime, at sites where BC monitoring is not available.

Estimation of radiative forcing and heating rate based on vertical observation of black carbon in Nanjing, China

Owing to a lack of vertical observations, the impacts of black carbon (BC) on radiative forcing (RF) have typically been analyzed using ground observations and assumed profiles. In this study, a UAV platform was used to measure high-resolution in-situ vertical profiles of BC, fine particles (PM2.5), and relevant meteorological parameters in the boundary layer (BL). Further, a series of calculations using actual vertical profiles of BC were conducted to determine its impact on RF and heating rate (HR). The results show that the vertical distributions of BC were strongly affected by atmospheric thermodynamics and transport. Moreover. Three main types of profiles were revealed: Type I, Type II, Type III, which correspond to homogenous profiles (HO), negative gradient profiles (NG), and positive gradient profiles (PG), respectively. Types I and II were related to the diurnal evolution of the BL, and Type III was caused by surrounding emissions from high stacks and regional transport. There were no obvious differences in RF calculated for HO profiles and corresponding surface BC concentrations, unlike for NG and PG profiles. RF values calculated using surface BC concentrations led to an overestimate of 13.2 W m−2 (27.5%, surface) and 18.2 W m−2 (33.4%, atmosphere) compared to those calculated using actual NG profiles, and an underestimate of approximately 15.4 W m−2 (35.0%, surface) and 16.1 W m−2 (29.9%, atmosphere) compared to those calculated using actual PG profiles. In addition, the vertical distributions of BC HR exhibited clear sensitivity to BC profile types. Daytime PG profiles resulted in a positive vertical gradient of HR, which may strengthen temperature inversion at high altitudes. These findings indicate that calculations that use BC surface concentrations and ignore the vertical distribution of BC will lead to substantial uncertainties in the effects of BC on RF and HR.

Impacts of atmospheric transport and biomass burning on the inter-annual variation in black carbon aerosols over the Tibetan Plateau

Abstract. Atmospheric black carbon (BC) in the Tibetan Plateau (TP) can largely impact regional and global climate. Still, studies on the inter-annual variation in atmospheric BC over the TP and associated variation in BC sources and controlling factors are rather limited. In this study, we characterize the variations in atmospheric BC over the TP surface layer through analysis of 20-year (1995–2014) simulations from a global chemical transport model, GEOS-Chem. The results show that surface BC concentrations over the TP vary largely in space and by season, reflecting complicated interplays of BC sources from different origins. Of all areas in the TP, surface BC concentrations are highest over the eastern and southern TP, where surface BC is susceptible to BC transport from East Asia and South Asia, respectively. Applying a backward-trajectory method that combines BC concentrations from GEOS-Chem and trajectories from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we assess the contributions of worldwide source regions to surface BC in the TP. We estimate that on the 20-year average, 77 % of surface BC in the TP comes from South Asia (43 %) and East Asia (35 %). Regarding seasonal variation in non-local influences, South Asia and East Asia are dominant source regions in winter and summer, respectively, in terms of the amount of BC imported. However, in terms of affected areas in the TP, South Asia is the dominant contributor throughout the year. Inter-annually, surface BC over the TP is largely modulated by atmospheric transport of BC from non-local regions year-round and by biomass burning in South Asia, mostly in spring. We find that the extremely strong biomass burning in South Asia in the spring of 1999 greatly enhanced surface BC concentrations in the TP (31 % relative to the climatology). We find that the strength of the Asian monsoon correlates significantly with the inter-annual variation in the amount of BC transported to the TP from non-local regions. In summer, a stronger East Asian summer monsoon and a stronger South Asian summer monsoon tend to, respectively, lead to more BC transport from central China and north-eastern South Asia to the TP. In winter, BC transport from central China is enhanced in years with a strong East Asian winter monsoon or a strong Siberian High. A stronger Siberian High can also bring more BC from northern South Asia to the TP. This study underscores the impacts of atmospheric transport and biomass burning on the inter-annual variation in surface BC over the TP. It reveals a close connection between the Asian monsoon and atmospheric transport of BC from non-local regions to the TP.

Regional and Sectoral Sources for Black Carbon Over South China in Spring and Their Sensitivity to East Asian Summer Monsoon Onset

AbstractBesides local emissions, biomass burning (BB) emissions in peninsula Southeast Asia (PSEA) and domestic anthropogenic emissions in North China (NC) are also significant black carbon (BC) sources over South China (SC) in spring. Meanwhile, the East Asian summer monsoon (EASM) is established with the wind field reversal, influencing the region‐based contributions to BC over SC. Herein, BC sources for SC were tracked by region and by sector using the Community Earth System Model with a BC‐tagging technique. During the spring of 2000–2014, 27% of BC surface concentration (BCS) and 64% of BC column burden (BCC) over SC stems from nonlocal sources. BC from NC is mainly transported below 850 hPa. It is the dominant nonlocal contribution to BCS (17%) and largely composed of residential and industrial sectors. Nonlocal emissions inside and outside China contribute 28% and 36% to BCC, respectively. Generally transported above 850 hPa, BC from PSEA is the largest nonlocal contributor (20%) to BCC and contributes 80% of BCC in BB sector. Additionally, the interannual variation in EASM onset times bring a maximum of −5% to +7%/−2% to +7% variation in BCC/BCS. The BC outflow/inflow contributed from NC dominates the BC decrease/increase over SC with southerly/northerly wind anomaly induced by early/late EASM onset, yet regional transport from PSEA contributes minor BC changes. The simulated BC is significantly positively correlated with the varying EASM onset times, but not with emissions, indicating the decisive role of meteorology in the interannual variation of BC over SC during springtime.

Estimating the Columnar Concentrations of Black Carbon Aerosols in China Using MODIS Products.

Black carbon (BC), the strongest light-absorbing particle, is believed to play substantial roles in regional air quality and global climate change. In this study, taking advantage of the high quality of moderate resolution imaging spectroradiometer products, we developed a new algorithm to estimate the BC columnar concentrations over China by simulating the BC and non-BC aerosol mixing states in detail. The results show that our new algorithm produces a reliable estimation of BC aerosols, in which BC columnar concentrations and their related parameters (aerosol absorption and BC surface concentration) show reasonable agreements and low biases compared with ground-based measurements. The uncertainties of BC retrievals are mainly associated with the surface and aerosol assumptions used in the algorithm, ranging from -14 to 44% at higher aerosol optical depth (AOD > 0.5). The proposed algorithm can improve the capability of space-borne aerosol remote sensing by successfully distinguishing BC from other aerosols. The acquired BC columnar concentrations enable the spatial pattern of serious BC aerosol pollution over East China to be characterized, showing that it exhibits higher levels in winter. These nationwide results are beneficial for estimating BC emissions, proposing mitigation strategies for air pollution, and potentially reducing the uncertainties of climate change studies.

Physically based model of the contribution of red snow algal cells to temporal changes in albedo in northwest Greenland

Abstract. Surface albedo of snow and ice is substantially reduced by inorganic impurities, such as aeolian mineral dust (MD) and black carbon (BC), and also by organic impurities, such as microbes that live in the snow. In this paper, we present the temporal changes of surface albedo, snow grain size, MD, BC and snow algal cell concentration observed on a snowpack in northwest Greenland during the ablation season of 2014 and our attempt to reproduce the changes in albedo with a physically based snow albedo model. We also attempt to reproduce the effects of inorganic impurities and the red snow algae (Sanguina nivaloides) on albedo. Concentrations of MD and red snow algae in the surface snow were found to increase in early August, while snow grain size and BC were found to not significantly change throughout the ablation season. Surface albedo was found to have decreased by 0.08 from late July to early August. The albedo simulated by the model agreed with the albedo observed during the study period. However, red snow algae exerted little effect on surface albedo in early August. This is probably owing to the abundance of smaller cells (4.9×104 cells L−1) when compared with the cell abundance of red snow reported by previous studies in the Arctic region (∼108 cells L−1). The simulation of snow albedo until the end of the melting season, with a snow algae model, revealed that the reduction in albedo attributed to red snow algae could equal 0.004, out of a total reduction of 0.102 arising from the three impurities on a snowpack in northwest Greenland. Finally, we conducted scenario simulations using the snow albedo model, coupled with the snow algae model, in order to simulate the possible effects of red snow blooming on snow albedo under warm conditions in northwest Greenland. The result suggests that albedo reduction by red snow algal growth under warm conditions (surface snow temperature of +1.5 ∘C) reached 0.04, equivalent to a radiative forcing of 7.5 W m−2 during the ablation season of 2014. This coupled albedo model has the potential to dynamically simulate snow albedo, including the effect of organic and inorganic impurities, leading to proper estimates of the surface albedo of snow cover in Greenland.