Carbonaceous aerosols and their light absorption properties over the Bay of Bengal during continental outflow.

The marine atmosphere of the Bay of Bengal (BoB) is prone to get impacted by anthropogenic aerosols from the Indo-Gangetic Plain (IGP) and Southeast Asia (SEA), particularly during the northeast monsoon (NEM). In this study, we quantify and characterize carbonaceous aerosols and their absorption properties collected in two cruise campaigns onboard ORV Sindhu Sadhana during the continental outflow period over the BoB. Aerosol samples were classified based on the air mass back trajectory analyses, wherein samples were impacted by the continental air parcel (CAP), marine air parcel (MAP), and mix of both (CAP + MAP). Significant variability in the PM10 mass concentration (in µg m-3) is found with a maximum value for MAP samples (75.5 ± 36.4) followed by CAP + MAP (58.5 ± 27.3) and CAP (58.5 ± 27.3). The OC/EC ratio (>2) and diagnostic tracers i.e. nss-K+/EC (0.2-0.96) and nss-K+/OC (0.11-1.32) along with the absorption angstrom exponent (AAE: 4.31-6.02) and MODIS (Moderate Resolution Imaging Spectroradiometer) derived fire counts suggest the dominance of biomass burning emission sources. A positive correlation between OC and EC (i.e. r = 0.86, 0.70, and 0.42 for CAP, MAP, and CAP + MAP, respectively) further confirmed the similar emission sources of carbonaceous species. Similarly, a significant correlation between estimated secondary organic carbon (SOC) and water-soluble organic carbon (WSOC; r = 0.99, 0.96, and 0.97 for CAP, MAP, and CAP + MAP, respectively) indicate their similar chemical nature as well as dominant contribution of SOC to WSOC. The absorption coefficient (babs-365) and mass absorption efficiency (MAEBrC-365) of the soluble fraction were estimated at 365 nm wherein, babs-365 showed a linear relationship with WSOC and nss-K+, signifying the contribution of water soluble brown carbon from biomass burning emissions. The estimated MAEBrC-365 (0.30-0.93 m2 g-1), during this study, was consistent with the earlier observations over the BoB, particularly during the continental outflow season.

Light absorption enhancement of particulate matters and their source apportionment over the Asian continental outflow site and South Yellow Sea.

Light absorption enhancement of black carbon due to the aerosol mixing states is an important parameterization for climate modeling, while emission source contributions to the enhancement factor are unclear. An intensive campaign was conducted simultaneously at a China coastal site (Qingdao city) and maritime sites (South Yellow Sea, SYS) in August and Nov to Dec 2018. The absorption enhancement (EMAC) of the black carbon was calculated using a two-step solvent dissolution protocol and found 1.96 ± 0.68, 1.64 ± 0.38, and 2.40 ± 0.76 for Qingdao summer (QS), Qingdao autumn (QA), and SYS, respectively. Positive matrix factorization (PMF) model identified six sources of PM2.5 and EMAC, which were secondary aerosol (with contribution 27.9% and 29.2%), coal combustion (24.9% and 20.2%), industrial emissions (15.2% and 25.4%), sea salt (6.9% and 9.6%), vehicle emissions (12.1% and 10.9%), and soil dust (13.0% and 4.7%), respectively. These sources increased the absorption of black carbon by a factor of 1.25 ± 0.11 (secondary aerosol), 1.21 ± 0.20 (industrial emissions), 1.17 ± 0.08 (coal combustion), 1.09 ± 0.07 (vehicle emissions), 1.08 ± 0.17 (sea salt), and 1.04 ± 0.10 (soil dust). Based on the correlation between PM and EMAC source contributions, we estimated that secondary aerosols, industrial emissions, and coal combustion contributed to 74.8% of absorption enhancement at a regional scale in China. The source apportionment for EMAC offers a new diagnosis for each source regarding aerosol forcing simulation which inputs from the individual emission sector.

Source apportionment of absorption enhancement of black carbon in different environments of China.

Black carbon (BC) is an important pollutant for both air quality and earth's radiation balance because of its strong absorption enhancement. The enhanced light absorption of BC caused by other pollutants is one of the most important sources of uncertainty in global radiative forcing. The light absorption of BC is highly dependent on the emission source and very few studies have been carried out for the source apportionment of BC absorption enhancement. Thus, with this objective, continuous measurements of particulate matter (PM2.5) were performed at three different sites: a traffic site in Nanjing, an urban site in Jinan, and a rural site in Yucheng; the BC absorption enhancement and its source contributions were determined. The mass absorption cross-section (MAC) of BC aerosols was reduced after the removal of the coating material. The maximum MAC enhancement (EMAC) was found to be 2.25 ± 0.5 at the rural site, followed by 2.07 ± 0.7 at the urban site and 1.7 ± 0.6 at the traffic site, suggesting an approximately double enhancement in BC absorption due to different coating materials. The source apportionment of absorption enhancement of BC analysis using the positive matrix factorization model suggests five major emission sources. Among them, secondary sources were the main source of EMAC at all the three sites with a percentage contribution of 43.4% (rural site), 34.6% (traffic site), and 31% (urban site). However, other emission sources, such as biomass burning (21.1% at rural site) and vehicular emissions (33.8% at traffic site) also had a significant contribution to EMAC, suggesting that there could be large variations in BC absorption enhancement due to differences in emission sources together with aerosol aging processes.

Spatial variability of sedimentary carbon in South Yellow Sea, China: impact of anthropogenic emission and long-range transportation.

During the last few decades, sedimentary carbons gain great concerns of research interest among the scientific committee worldwide due to their adverse impact on aquatic chemistry, ecology, and hence human health along with global climate change. In the present study, we investigated the spatial distribution of mass concentration of sedimentary carbon (viz. black carbon: BC, and its components, char and soot) along with their burial fluxes in the surface sediments of the South Yellow Sea (SYS). The concentration of sedimentary carbon is measured by using an emerging method of thermal/optical reflectance. The observed BC concentration is found in the range of 0.02-1.02 mg g-1 with a mean value of 0.49 ± 0.26 mg g-1. The mean burial fluxes of BC, char, and soot also have a similar spatial variation to their concentration with the mean value along with relative standard deviation (in bracket) 22.43 ± 12.49 (~ 56%), 5.90 ± 3.99 (~ 68%), and 16.53 ± 10.67 (65%), respectively. Relatively lower value of char/soot ratio, i.e., 0.48 ± 0.22, indicates the dominance of soot in surface sediments that could be mainly derived from the fossil fuel combustion which is further confirmed from emission inventory data suggesting maximum contribution, i.e., ~ 66-80%, of the total BC emission emitted from residential and industrial emission sources. The back trajectories analysis revealed a significant impact of long-range transportation on BC concentration in the surface sediments of SYS. Further study of BC concentrations in sea sediments and their interaction with other organic/inorganic compounds in continental shelves is highly needed for a better understanding of the global carbon cycle.

Assessment of trends and emission sources of heavy metals from the soil sediments near the Bohai Bay.

Anthropogenic emission sources (mainly vehicular and industrial emission) are one of the major emission sources of the heavy metals in aquatic ecosystems which have significant potential to perturb the marine geochemistry and ecosystem as well as human life also. In the present study, we tried to investigate the accumulation of heavy metals (Zn, Cr, Ni, Cu, Pb, Co, As, Cd, and Hg) at two sediment cores near the Bohai Bay in Southern Tianjin and reconstruct their historical trends over the last hundred years to understand the impacts of anthropogenic activities. The concentration of Zn and Cr is found maximum than the other studied heavy metals. Results suggest that in the mid-twentieth century, the maximum concentrations of Zn, Cr, Ni, Cu, and Pb are mainly because of the opening of Dagang Oilfield which emits a huge amount of heavy metals into the environment. Source apportionment analysis has been carried out using positive matrix factorization (PMF) model which suggests three major emission sectors of heavy metals, i.e., coal combustion, manufacturing, and smelting dust, having different contribution 32%, 40%, and 28% respectively to the total heavy metal burden. Industrial emissions are found to be the major sources of Cr, Ni, and Co while Pb is mainly originated from the coal combustion. The risk assessment analysis shows the value of mean effects range median (ERM) quotients ~ 0.17 for the two sediment cores which suggest nearly 21% toxicity of the studied metals indicating towards the policymakers for the mitigation of air pollution surrounding Tianjin.

Aerosol columnar characteristics and their heterogeneous nature over Varanasi, in the central Ganges valley.

The Indo-Gangetic Basin (IGB) experiences one of the highest aerosol loading over the globe with pronounced inter-/intra-seasonal variability. Four-year (January 2011-December 2014) continuous MICROTOPS-II sun-photometer measurements at Varanasi, central Ganges valley, provide an opportunity to investigate the aerosol physical and optical properties and their variability. A large variation in aerosol optical depth (AOD: from 0.23 to 1.89, mean of 0.82 ± 0.31) and Ångström exponent (AE: from 0.19 to 1.44, mean of 0.96 ± 0.27) is observed, indicating a highly turbid atmospheric environment with significant heterogeneity in aerosol sources, types and optical properties. The highest seasonal means of both AOD and AE are observed in the post-monsoon (October-November) season (0.95 ± 0.31 for AOD and 1.16 ± 0.14 for AE) followed by winter (December, January, February; 0.97 ± 0.34 for AOD and 1.09 ± 0.20 for AE) and are mainly attributed to the accumulation of aerosols from urban and biomass/crop residue burning emissions within a shallow boundary layer. In contrast, during the pre-monsoon and monsoon seasons, the aerosols are mostly coming from natural origin (desert and mineral dust) mixed with pollution in several cases. The spectral dependence of AE, the aerosol "curvature" effect and other graphical techniques are used for the identification of the aerosol types and their mixing processes in the atmosphere. Furthermore, the aerosol source-apportionment assessment using the weighted potential source contribution function (WPSCF) analysis reveals the different aerosol types, emission sources and transport pathways.

Study of the carbonaceous aerosol and morphological analysis of fine particles along with their mixing state in Delhi, India: a case study.

Because of high emissions of anthropogenic as well as natural particles over the Indo-Gangetic Plains (IGP), it is important to study the characteristics of fine (PM2.5) and inhalable particles (PM10), including their morphology, physical and chemical characteristics, etc., in Delhi during winter 2013. The mean mass concentrations of fine (PM2.5) and inhalable (PM10) (continuous) was 117.6 ± 79.1 and 191.0 ± 127.6 µg m(-3), respectively, whereas the coarse mode (PM10-2.5) particle PM mass was 73.38 ± 28.5 µg m(-3). During the same period, offline gravimetric monitoring of PM2.5 was conducted for morphological analysis, and its concentration was ~37 % higher compared to the continuous measurement. Carbonaceous PM such as organic carbon (OC) and elemental carbon (EC) were analyzed on the collected filters, and their mean concentration was respectively 33.8 and 4.0 µg m(-3) during the daytime, while at night it was 41.2 and 10.1 µg m(-3), respectively. The average OC/EC ratio was 8.97 and 3.96 during the day and night, respectively, indicating the formation of secondary organic aerosols during daytime. Effective carbon ratio was studied to see the effect of aerosols on climate, and its mean value was 0.52 and 1.79 during night and day, indicating the dominance of absorbing and scattering types of aerosols respectively into the atmosphere over the study region. Elemental analysis of individual particles indicates that Si is the most abundant element (~37-90 %), followed by O (oxide) and Al. Circularity and aspect ratio was studied, which indicates that particles are not perfectly spherical and not elongated in any direction. Trajectory analysis indicated that in the months of February and March, air masses appear to be transported from the Middle Eastern part along with neighboring countries and over Thar Desert region, while in January it was from the northeast direction which resulted in high concentrations of fine particles.