Atmospheric Black Carbon Research Articles

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.

Historical variation of black carbon and PAHs over the last ~200 years in central North China: Evidence from lake sediment records

As the largest coal-producing province in China, the coal production of Shanxi Province accounts for one third of the country's total. Thus it is of great importance to study the pollution history of typical pollutants in Shanxi Province and their links with energy usage in North China. Sediment cores from two relatively remote lakes in central North China were retrieved to investigate historical evolutions of black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) in the last ~200 years. The two records show several-fold increases in both concentrations and depositional fluxes of BC, char, soot, and PAHs in recent five decades, which were associated with the influence of anthropogenic activities resulting from socio-economic development in Shanxi Province. However, after ~2000 their fluxes decreased sharply due to China's effort on environmental protection. These changes indicate that atmospheric BC and PAHs loads in the region were affected significantly by recent anthropogenic activities and environmental policies. Ratios of individual PAHs and char/soot indicate pyrogenic sources of these increased pollutants in recent decades, with coking industry and coal combustion as the two major sources. Significant positive correlations between BC and PAHs were observed in both cores of Lake Gonghai and Lake Mayinghai, indicating that they were likely co-transported by BC particles from similar sources. This study provides new and important understanding of the atmospheric pollution history of BC and PAHs in North China.

The application of Raman spectroscopy combined with multivariable analysis on source apportionment of atmospheric black carbon aerosols

Source apportionment studies become increasingly crucial for black carbon (BC) in atmospheric particulate matters given its linkage with adverse public health and climate impacts. In this work, a facile and rapid method using Raman spectra combined with stepwise discriminant analysis (SDA) was proposed to identify and quantify the contributions of atmospheric BC sources. Four BC samples from biomass burning, coal combustion, gasoline and diesel vehicle emission were characterized by Raman spectra. The SDA model was established based on 10 parameters with significant differences (p < 0.05), giving an accuracy of 83% with a cross-validation rate of 80%. Utilizing four suggested discriminant variables from SDA model, vehicle emission was predicted as the dominant contributor to ambient BC particles, among which gasoline contributed much higher than diesel at an urban road intersection in Shanghai, China. This new method shows great potential to classify and investigate the sources of atmospheric BC aerosols and provide more effective information on air pollution control measures.

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.

Relationship between long-range transported atmospheric black carbon and carbon monoxide at a high-altitude background station in East Asia

Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E; 2862 m above sea level) at the summit of Mount Lulin in central Taiwan was established in spring 2006 and is the only high-altitude background station over western Pacific region in East Asia to study the impact of various air pollutants through long-range transport. Continuous in-situ measurements of equivalent black carbon (EBC) and carbon monoxide (CO) concentrations were made at LABS from June 2012 to May 2014 and their association was investigated in this study. The highest monthly concentration of EBC (median; 840 ng m−3) and CO (212 ppbv) in March were primarily attributed to the westerly winds coupled with biomass-burning (BB) emissions from Southeast Asia (SEA) region. The association of EBC and CO was weak at LABS possibly due to the influence of dissimilar air masses from various sources, and scavenging or dilution of EBC during the long-range atmospheric transport to Mt. Lulin. The mean ΔEBC/ΔCO ratio (slope of least-squares regression line of ΔEBC-ΔCO scatterplot; where Δ indicates surplus amounts with respect to the background value) was found the most significant in March (5.3 ng m−3 ppbv−1 or 7.3 × 10−3 g of carbon as EBC per gram of carbon as CO). On the basis of episodic cases, the mean ΔEBC/ΔCO ratios at LABS were estimated to be 6.1, 8.0, and 2.4 ng m−3 ppbv−1 for SEA BB emissions, southern China mixed pollution, and northern China mixed pollution, respectively. A total of 32% loss in EBC aerosols (6.4% of EBC removal per day) was estimated for the atmospheric transport of BB emissions from SEA region to LABS. This study provides needful information to understand the ΔEBC/ΔCO ratios at a remote site and would be used in model simulations to evaluate BC aging and scavenging over western Pacific region in East Asia.

Biogeochemical Impacts of a Black Carbon Wet Deposition Event in Halong Bay, Vietnam

Black carbon (BC) is emitted to the atmosphere during biomass, biofuel and fossil fuel combustion, and leaves the atmosphere via dry or wet deposition on land and on the ocean. On a global scale, wet deposition accounts for about 80% of the total atmospheric BC inputs to the ocean. The input of BC particles to the ocean can enrich surface waters with carbon and associated elements, and owing to high porosity and surface-active properties, BC can alter biogeochemical cycles by sorbing dissolved compounds and promoting aggregation. The rain-mediated input of BC to the ocean and its consequences on nutrient concentrations and particle dynamics were studied in Halong Bay, Vietnam, during a 24 h cycle impacted by short and heavy rainfall events. This study suggests that once introduced in the surface ocean via wet deposition, BC sorbs dissolved organic matter (DOM) and stimulates aggregation processes. The observed wet deposition events were characterized by sudden and pulsed inputs of BC particles that created a thin layer of sinking surface-active aggregates, acting as a net-like scavenger for DOM, nutrients (especially phosphate), and small particles. In addition, the wet deposition events coincided with an enrichment of nutrients in the surface microlayer, with an excess input of nitrogen relative to phosphorus leading to an increase of the molar N:P ratio from 24:1 to 37:1. In the underlying water, the molar N:P ratio also increased (i.e., from 39:1 to 64:1), and this can be attributed to the preferential scavenging of dissolved P-compounds on sinking BC-aggregates.

Droplet activation behaviour of atmospheric black carbon particles in fog as a function of their size and mixing state

Abstract. Among the variety of particle types present in the atmosphere, black carbon (BC), emitted by combustion processes, is uniquely associated with harmful effects to the human body and substantial radiative forcing of the Earth. Pure BC is known to be non-hygroscopic, but its ability to acquire a coating of hygroscopic organic and inorganic material leads to increased diameter and hygroscopicity, facilitating droplet activation. This affects BC radiative forcing through aerosol–cloud interactions (ACIs) and BC life cycle. To gain insights into these processes, we performed a field campaign in winter 2015–2016 in a residential area of Zurich which aimed at establishing relations between the size and mixing state of BC particles and their activation to form droplets in fog. This was achieved by operating a CCN counter (CCNC), a scanning mobility particle sizer (SMPS), a single-particle soot photometer (SP2) and an aerosol chemical speciation monitor (ACSM) behind a combination of a total- and an interstitial-aerosol inlet. Our results indicate that in the morning hours of weekdays, the enhanced traffic emissions caused peaks in the number fraction of externally mixed BC particles, which do not act as CCN within the CCNC. The very low effective peak supersaturations (SSpeak) occurring in fog (between approximately 0.03 % and 0.06 % during this campaign) restrict droplet activation to a minor fraction of the aerosol burden (around 0.5 % to 1 % of total particle number concentration between 20 and 593 nm) leading to very selective criteria on diameter and chemical composition. We show that bare BC cores are unable to activate to fog droplets at such low SSpeak, while BC particles surrounded by thick coating have very similar activation behaviour to BC-free particles. Using simplified κ-Köhler theory combined with the ZSR mixing rule assuming spherical core–shell particle geometry constrained with single-particle measurements of respective volumes, we found good agreement between the predicted and the directly observed size- and mixing-state-resolved droplet activation behaviour of BC-containing particles in fog. This successful closure demonstrates the predictability of their droplet activation in fog with a simplified theoretical model only requiring size and mixing state information, which can also be applied in a consistent manner in model simulations.

Source apportionment of circum-Arctic atmospheric black carbon from isotopes and modeling.

Black carbon (BC) contributes to Arctic climate warming, yet source attributions are inaccurate due to lacking observational constraints and uncertainties in emission inventories. Year-round, isotope-constrained observations reveal strong seasonal variations in BC sources with a consistent and synchronous pattern at all Arctic sites. These sources were dominated by emissions from fossil fuel combustion in the winter and by biomass burning in the summer. The annual mean source of BC to the circum-Arctic was 39 ± 10% from biomass burning. Comparison of transport-model predictions with the observations showed good agreement for BC concentrations, with larger discrepancies for (fossil/biomass burning) sources. The accuracy of simulated BC concentration, but not of origin, points to misallocations of emissions in the emission inventories. The consistency in seasonal source contributions of BC throughout the Arctic provides strong justification for targeted emission reductions to limit the impact of BC on climate warming in the Arctic and beyond.

Sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan: The roles of Siberian wildfires and of crop residue burning in China

A field study was conducted to clarify sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan. We quantified equivalent black carbon (eBC) particle mass and the absorption Ångström exponent (AAE), atmospheric CO and CH4, in addition to levoglucosan in total suspended particles, a typical tracer of biomass burning. Sixteen high eBC events were identified attributable to either anthropogenic sources or biomass burning in Siberia/China. These events were often accompanied by increases of co-emitted gases such as CH4 and CO. Specifically, we observed pollution events with elevated eBC, AAE, levoglucosan, and CH4CO slope in late July 2014, which were attributed to forest fires in Siberia by reference to the FLEXPART model footprint and fire hotspots. In autumn, drastic increases of eBC, AAE, and levoglucosan were observed, accompanied by an eBC–CO slope of >15 ng m−3/ppb, resulting from long-range transport of emissions from extensive burning of crop residue on the Northeast China Plain. Other than the sources of fossil fuel combustion in China and forest fires in Siberia, we report for the first time that pollution events in northern Japan are caused by crop residue burning in China. This study elucidated valuable information that will improve understanding of the effects of biomass burning in East Asia on atmospheric carbonaceous components.

Concentrations and radiative forcing of anthropogenic aerosols from 1750 to 2014 simulated with the Oslo CTM3 and CEDS emission inventory

Abstract. We document the ability of the new-generation Oslo chemistry-transport model, Oslo CTM3, to accurately simulate present-day aerosol distributions. The model is then used with the new Community Emission Data System (CEDS) historical emission inventory to provide updated time series of anthropogenic aerosol concentrations and consequent direct radiative forcing (RFari) from 1750 to 2014. Overall, Oslo CTM3 performs well compared with measurements of surface concentrations and remotely sensed aerosol optical depth. Concentrations are underestimated in Asia, but the higher emissions in CEDS than previous inventories result in improvements compared to observations. The treatment of black carbon (BC) scavenging in Oslo CTM3 gives better agreement with observed vertical BC profiles relative to the predecessor Oslo CTM2. However, Arctic wintertime BC concentrations remain underestimated, and a range of sensitivity tests indicate that better physical understanding of processes associated with atmospheric BC processing is required to simultaneously reproduce both the observed features. Uncertainties in model input data, resolution, and scavenging affect the distribution of all aerosols species, especially at high latitudes and altitudes. However, we find no evidence of consistently better model performance across all observables and regions in the sensitivity tests than in the baseline configuration. Using CEDS, we estimate a net RFari in 2014 relative to 1750 of −0.17 W m−2, significantly weaker than the IPCC AR5 2011–1750 estimate. Differences are attributable to several factors, including stronger absorption by organic aerosol, updated parameterization of BC absorption, and reduced sulfate cooling. The trend towards a weaker RFari over recent years is more pronounced than in the IPCC AR5, illustrating the importance of capturing recent regional emission changes.

Perturbations in atmospheric gaseous components over coastal Antarctica detected in GPS signals and its natural origin to volcanic eruption

Although the variations in atmospheric water content control the perturbations in total travel time delay experienced by GPS signals during passage through the atmosphere (ZTD-Zenith Total Delay), significant changes in ZTD can also occur due to anomalous high influx of dry components into the atmosphere during massive volcanic eruptions. Such a possibility is illustrated here by analyzing GPS data from different locations around the Antarctic continent during the massive eruption of Mt. Chaiten volcano in Chile on 19th, February 2009. GPS derived ZTD values showed abnormal perturbation during the transition from summer to winter time in Antarctic margins. The irregular ZTD values, which existed for the short period from 19th, February to 08th, March 2009, exhibited perturbations and showed high correspondence with the abnormal atmospheric black carbon (BC) content noticed over the Indian Antarctic station (Maitri) during the same period. We therefore suggest that the anomalous ZTD changes might have resulted due to high BC influx into the atmosphere. We propose that the 19th, February 2009 massive eruption of Mt. Chaiten is the source for the BC, which moved from the volcanic front to the East Antarctica margin along with the circum polar current.

Evidence of major secondary organic aerosol contribution to lensing effect black carbon absorption enhancement

Atmospheric black carbon (BC) has a strong positive, but still controversial, effect on global warming. In particular, BC absorption enhancement (Eabs) due to internal mixing with other chemical species—so-called lensing effect—is poorly assessed. This bottleneck partly relies on the lack of long-term in situ measurements of both the optical and chemical properties of BC-containing particles. Here, we present experimental and computational results showing a significant Eabs increase with the aerosol photochemical aging. This was associated with the production of highly oxidized secondary organic aerosols (SOA), especially at summertime. The 3-year-long continuous aerosol chemical and optical measurements used for the present study was obtained in the Paris region, France, which might be representative of near-future air quality within developing countries. These findings suggest that SOA could represent one of the most critical chemical species to be considered within climate models.

The influence of photochemical aging on light absorption of atmospheric black carbon and aerosol single-scattering albedo

Abstract. Coating enhancement of black carbon (BC) light absorption (Eabs) is a large uncertainty in modelling direct radiative forcing (DRF) by BC. Reported Eabs values after atmospheric aging vary widely and the mechanisms responsible for enhancing BC absorption remain elusive. Here, we report on the direct field measurement of size-resolved mixing state, Eabs, and aerosol single-scattering albedo (SSA) at λ = 532 nm at a rural site in east China from June to July 2016. Strong diurnal variability of Eabs, SSA, and Ox (Ox = NO2 + O3, a proxy for atmospheric photochemical aging) was observed. A method that combined Eabs and SSA was developed to retrieve the fraction contribution of BC absorption (fBC), lensing-driven enhancement (fLens), as well as the fractional contribution of coating absorption (fraction absorption contribution (fShell), the coated shell diameter (DShell) and the imaginary part of the complex refractive index (CRI) of the shell (kShell)). Parameterization of Eabs and SSA captures much of the influence of BC coating and the particle absorption. In our measurements at this site, the results showed that the absorption amplification depended on the coating thickness and the absorption of coating materials, and photochemistry plays a role in modifying the absorption of BC-containing particles. The lensing-driven enhancement was reduced by light absorption of the shell. One implication of these findings is that the contribution of light-absorbing organic compounds (brown carbon, BrC) at a longer aging time should be included in climate models.

Cloud droplet activation of black carbon particles coated with organic compounds of varying solubility

Abstract. Atmospheric black carbon (BC) particles are a concern due to their impact on air quality and climate. Their net climate effect is, however, still uncertain. This uncertainty is partly related to the contribution of coated BC particles to the global cloud condensation nuclei (CCN) budgets. In this study, laboratory measurements were performed to investigate CCN activity of BC (REGAL 400R pigment black) particles, in pure state or coated through evaporating and subsequent condensation of glutaric acid, levoglucosan (both water-soluble organics) or oleic acid (an organic compound with low solubility). A combination of soot particle aerosol mass spectrometer (SP-AMS) measurements and size distribution measurements with a scanning mobility particle sizer (SMPS) showed that the studied BC particles were nearly spherical agglomerates with a fractal dimension of 2.79 and that they were coated evenly by the organic species. The CCN activity of BC particles increased after coating with all the studied compounds and was governed by the fraction of organic material. The CCN activation of the BC particles coated by glutaric acid and levoglucosan were in good agreement with the theoretical calculations using the shell-and-core model, which is based on a combination of the CCN activities of the pure compounds. The oleic acid coating enhanced the CCN activity of the BC particles, even though the pure oleic acid particles were CCN inactive. The surprising effect of oleic acid might be related to the arrangement of the oleic acid molecules on the surface of the BC cores or other surface phenomena facilitating water condensation onto the coated particles. Our results show that present theories have potential for accurately predicting the CCN activity of atmospheric BC coated with organic species, given that the identities and amounts of the coating species are known. Furthermore, our results suggest that even relatively thin soluble coatings (around 2 nm for the compounds studied here) are enough to make the insoluble BC particles CCN active at typical atmospheric supersaturations and thus be efficiently taken up by cloud droplets. This highlights the need for an accurate description of the composition of atmospheric particles containing BC to unravel their net impact on climate.

Black carbon radiative effects highly sensitive to emitted particle size when resolving mixing-state diversity

Post-industrial increases in atmospheric black carbon (BC) have a large but uncertain warming contribution to Earth’s climate. Particle size and mixing state determine the solar absorption efficiency of BC and also strongly influence how effectively BC is removed, but they have large uncertainties. Here we use a multiple-mixing-state global aerosol microphysics model and show that the sensitivity (range) of present-day BC direct radiative effect, due to current uncertainties in emission size distributions, is amplified 5–7 times (0.18–0.42 W m−2) when the diversity in BC mixing state is sufficiently resolved. This amplification is caused by the lifetime, core absorption, and absorption enhancement effects of BC, whose variability is underestimated by 45–70% in a single-mixing-state model representation. We demonstrate that reducing uncertainties in emission size distributions and how they change in the future, while also resolving modeled BC mixing state diversity, is now essential when evaluating BC radiative effects and the effectiveness of BC mitigation on future temperature changes.

Status of atmospheric particulate matter and black carbon concentration at Ashuganj in Brahmanbaria

Atmospheric particulate matter (PM) samples (both PM10 and PM2.5) were collected simultaneously from Midland Power Company Limited at Ashuganj, in Brahmanbaria to monitor the seasonal fluctuations of particulate matter and black carbon (BC) concentrations from air samples. Total eight samples were collected from January 2016 to December 2017 using two Air Metrics MiniVol samplers and the quantity of PM2.5 and PM10 was detected by weighing the filters before and after exposure. The concentration of PM (PM2.5 and PM10) and BC were analyzed at the laboratory of Chemistry Division, Atomic Energy Centre, Dhaka. The black carbon concentration from both PM2.5 and PM10 samples were also determined by reflectance measurement. The concentrations of PM2.5 varied from 12.2–145 μgm−3 where mean value was 67.09 μgm−3. The mean concentration of PM10 was 103.64 μgm−3 whereas the concentration ranged from 20.5–220 μgm−3. The ratios of PM2.5/PM10 fluctuated during different seasons, winter showed higher concentration and summer showed relatively lower concentration for both PM2.5 and PM10. Atmospheric dispersion due to increased wind speeds and wider mixing layer heights are recognized to be responsible for the lower PM concentrations in warmer months. The concentrations of BC in PM2.5 also varied from 2.44–33.4 μgm−3 and BC in PM10 varied from 4.51–57.2 μgm−3, respectively. The concentrations of particulate matter exceeded the Bangladesh National Ambient Air Quality Standard.J. Bangladesh Agril. Univ. 16(2): 232-236, August 2018

Realizing the opportunities of black carbon in urban soils: Implications for water quality management with green infrastructure

Soils and associated microbial processes regulate the carbon cycle and provide a sink for atmospheric black carbon (BC). Particularly in urban areas, present and accumulated soil BC may act as an effective sorbent of anthropogenic contaminants in green spaces. We characterized carbon concentrations that have accumulated in urban soils (organic carbon, BC, and inorganic C) and determined soil physical attributes (soil texture, hydraulic conductivity) from urban soil assessments (surface and sub-surface horizons) carried out in eleven cities in the United States. We used both ordinary least squares and non-parametric classification and regression tree (CART) methods to discern trends in soil BC concentrations with regard to soil, landscape, and emission characteristics. We found that for all cities, regional traffic density and vegetation were good predictors of soil BC concentration. Additionally, the thickness of the top soil horizon explained additional variation in sub-surface BC concentrations. Sites with coincident BC stocks and favorable infiltration rate were discussed as per their potential for improving water quality in multifunctional green infrastructure installations. In the broader sense, the high sorption capacity of existing, accumulated soil BC can contribute to regulation of contaminant cycling in urban areas and may enhance the overall value of urban soils in terms of ecosystem services.

Characterization of atmospheric Black Carbon over a semi-urban site of Southeast India: Local sources and long-range transport

Continuous measurements of Black Carbon (BC) mass concentration using an advanced multi wavelength Aethalometer (AE-33) during January–December 2016 were carrried out, for the first time, at the premises of KL University, Vijayawada (16.44°N, 80.62°E, 30 m amsl), a semi-urban site in the southeast India. The estimates of the percentage contribution of Biomass Burning (BB%) aerosols to total BC concentration is utilised to understand the contribution of anthropogenic activities over the observational site. In this context, the diurnal and seasonal variation of BC mass concentrations and BB (%) contributions have been investigated and the possible sources are examined. A significant diurnal variation in BC concentration is observed with two prominent peaks, one occuring in the morning hours (around 0800–0900 IST) and the other occuring in the evening hours (around 2000 IST). Annually, the maximum BC concentration is observed during November (6.88 ± 1.56 μg m−3) and minimum during August (1.7 ± 0.52 μg m−3) over this location. On a seasonal scale, mean BC mass concentration is highest during winter (DJF, 4.68 ± 1.32 μg m−3) followed by post-monsoon (SON, 4.52 ± 2.36 μg m−3), summer (MAM, 2.44 ± 0.8 μg m−3) and lowest during monsoon (JJA, 1.83 ± 0.61 μg m−3). The higher BB (%) contribution is observed during summer (25.21 ± 7.02%), while the contribution is minimum in monsoon season (16.83 ± 4.15%). Examination of the spectral properties of aerosol absorption in terms of Ångström exponent (α) indicates that the major contributor of BC over this location is biomass burning (α ~ 1.66 ± 0.06). This is supported by the higher number of fire counts (obtained from Moderate Resolution Imaging Spectroradiometer-MODIS onboard Terra satellite) in and around the study region during winter and summer revealing the higher contribution of BB aerosols. The concentration weighted trajectories (CWT) analysis (based on 5-day airmass back trajectories arriving the receptor site at an altitude of 500 m AGL) reveals that synoptic airmasses arriving from the continental regions located northeast of the observational sites mainly influence the BC properties over Vijayawada.

Influence of Emissions and Aqueous Processing on Particles Containing Black Carbon in a Polluted Urban Environment: Insights From a Soot Particle‐Aerosol Mass Spectrometer

AbstractInorganic and organic coatings on black carbon (BC) particles can enhance light absorption and affect atmospheric lifetimes of BC‐containing particles and thus have significant implications for climate. To study the physical and chemical characteristics of atmospheric BC and BC‐associated coatings, a soot particle‐aerosol mass spectrometer was deployed during the winter of 2014–2015 in Fresno, a city located in the San Joaquin Valley of California, to selectively analyze BC‐containing particles. Comparing soot particle‐aerosol mass spectrometer measurements to those from the collocated single‐particle soot photometer (SP2) and high‐resolution aerosol mass spectrometer, we found that 17% of total submicrometer aerosol mass was associated with BC‐containing particles, suggesting that a majority of the fine particles in Fresno contained no BC. Most BC‐containing particles appeared to be associated with residential wood burning and vehicular traffic. These particles typically had a bulk‐average mass ratio of coating to BC (Rcoat/rBC) less than 2. However, during periods of persistent fog larger Rcoat/rBC values were observed, with the coatings primarily composed of secondary inorganic and organic components that likely resulted from aqueous‐phase processing. Specifically, compared to periods with less fog, the BC coating increased in concentration and contained a larger fraction of nitrate and oxidized organic matter. The size distributions of BC and associated organic coating were generally centered around 300 nm in vacuum aerodynamic diameter. However, during foggy periods BC had an additional peak at ~400 nm and organics and nitrate displayed a prominent mode in the accumulation size range.