Black Carbon Mass Research Articles

A methodology to relate black carbon particle number and mass emissions

Black carbon (BC) particle number (PN) emissions from various sources contribute to the deterioration of air quality, adverse health effects, and anthropogenic climate change. This paper critically reviews different fractal aggregate theories to develop a new methodology that relates BC PN and mass concentrations (or emissions factors). The new methodology, named as the fractal aggregate (FA) model is validated with measurements from three different BC emission sources: an internal combustion engine, a soot generator, and two aircraft gas turbine engines at ground and cruise conditions. Validation results of the FA model show that R2 values range from 0.44 to 0.95, while the Normalised Mean Bias is between −27.7% and +26.6%. The model estimates for aircraft gas turbines represent a significant improvement compared to previous methodologies used to estimate aviation BC PN emissions, which relied on simplified assumptions. Uncertainty and sensitivity analyses show that the FA model estimates have an asymmetrical uncertainty bound (−54%,+103%) at a 95% confidence interval for aircraft gas turbine engines and are most sensitive to uncertainties in the geometric standard deviation of the BC particle size distribution. Given the improved performance in estimating BC PN emissions from various sources, we recommend the implementation of the FA model in future health and climate assessments, where the impacts of PN are significant.

The evolution of an aerosol event observed from aircraft in Beijing: An insight into regional pollution transport

To investigate the transport and formation mechanism of pollution in Beijing, this study explored the vertical profiles of aerosol properties using aircraft measurement during a regional transport (RT) pollution event from 10th to 12th December 2016. The aerosol chemical composition and size distribution were characterized. Different vertical structures exhibited during three periods (defined as before RT, during RT, and after RT) for this pollution event. Before RT, PM2.5 and black carbon (BC) mass loading were at low level in the mixing layer (ML) when the clean northerly air mass dominated. During RT, an elevated aerosol layer, in which BC and PM2.5 mass concentrations were about 1.5 times higher than that at the ground level, was found in the upper ML (at 400–900 m) over Beijing. This elevated aerosol layer was advected by the prevailing southwesterly air mass which transported the pollutants from the intensively polluted southwestern region over Beijing. These aerosols through RT featured with pronounced secondary compositions and large coatings on BC particles. After RT, the pollutants were significantly diluted by the prevailing NW air mass, whereas the aerosol concentration almost maintained in the near surface, leading to notable vertical gradient. The continued surface pollution may result from the low wind speed and secondary aerosol formation in the next day. This study suggests that only the ground observation could not fully explain the pollution event, but the variation of vertical structure of aerosol properties should be considered to elucidate the formation mechanism of pollution over Beijing.

Decreasing Trend in Black Carbon Aerosols Over the Indian Region

AbstractWe examine long‐term trends in the near‐surface black carbon mass concentration, using multiyear primary data obtained from a dense network (ARFINET) of observatories over the Indian region. We report for the first time the statistically significant decreasing trend in black carbon mass concentration, based on primary data from this region, at an average rate of ~242 ± 53 ng · m−3 · year−1 during the period 2007–2016. This finding contrasts with the generally increasing trend in the columnar aerosol optical depth, reported earlier, and the steadily increasing trend in anthropogenic activities over this region. The roles of different possible mechanisms, including possible changes in the vertical redistribution of aerosols, are discussed. Over the period 2007–2015, a significant though weak, increasing trend is seen in the contribution from aerosols above 1 km to the columnar aerosol optical depth. These observations imply possible long‐term climate consequences.

Comparison of measurement methods for the characterization of the black carbon emissions from a T63 turboshaft engine burning conventional and Fischer-Tropsch fuels

ABSTRACTEmission measurements of black carbon (BC) mass were conducted on a T63 turboshaft engine, operated at idle and cruise power with conventional and alternative fuels, using an Artium LII-300 laser-induced incandescence analyzer (LII) and AVL model 483 micro soot sensor (MSS) photoacoustic instrument using the manufacturer’s calibration for both instruments. These measurements were compared with elemental carbon (EC) determined by manual and semicontinuous thermal-optical transmission analyses according to National Institute for Occupational Safety and Health (NIOSH) method 5040 as the reference method. The results indicate that both the LII and MSS instruments show good linear correlation with EC for the two fuels and two engine power conditions evaluated. The LII measurements were observed to be biased high (27–49%) and the MSS measurements were biased low (24–35%) relative to EC. The agreement between the instruments and the reference method was substantially improved by applying a calibration of the instruments against a common BC aerosol source. Test data also suggest that the two instruments show some sensitivity to particle size (or properties related to size), specifically for particles with a geometric mean diameter (GMD) <30 nm. This sensitivity is problematic, since new engines or certain combustion conditions in current engines will produce smaller particles compared with the T63 model tested in this study. Further assessments of instrument performance for particles within this size range are therefore warranted.Implications: Accurate black carbon emission measurements are needed to certify new and in-production commercial aircraft engines. Both the Artium LII-300 and AVL 483 micro soot sensor are currently approved by the International Civil Aviation Organization for this purpose. This study compares the two instruments against elemental carbon (EC) using NIOSH method 5040 as the reference using a T63 turboshaft engine. The results indicate that both instruments correlate reasonably well with EC, and the correlation substantially improved when applying a calibration against a common aerosol source. Sensitivity to particle size may be an issue for both instruments.

High Arctic aircraft measurements characterising black carbon vertical variability in spring and summer

Abstract. The vertical distribution of black carbon (BC) particles in the Arctic atmosphere is one of the key parameters controlling their radiative forcing and thus role in Arctic climate change. This work investigates the presence and properties of these light-absorbing aerosols over the High Canadian Arctic (&gt;70∘ N). Airborne campaigns were performed as part of the NETCARE project (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) and provided insights into the variability of the vertical distributions of BC particles in summer 2014 and spring 2015. The observation periods covered evolutions of cyclonic disturbances at the polar front, which favoured the transport of air pollution into the High Canadian Arctic, as otherwise this boundary between the air masses largely impedes entrainment of pollution from lower latitudes. A total of 48 vertical profiles of refractory BC (rBC) mass concentration and particle size, extending from 0.1 to 5.5 km altitude were obtained with a Single-Particle Soot Photometer (SP2). Generally, the rBC mass concentration decreased from spring to summer by a factor of 10. Such depletion was associated with a decrease in the mean rBC particle diameter, from approximately 200 to 130 nm at low altitude. Due to the very low number fraction, rBC particles did not substantially contribute to the total aerosol population in summer. The analysis of profiles with potential temperature as vertical coordinate revealed characteristic variability patterns within specific levels of the cold and stably stratified, dome-like, atmosphere over the polar region. The associated history of transport trajectories into each of these levels showed that the variability was induced by changing rates and efficiencies of rBC import. Generally, the source areas affecting the polar dome extended southward with increasing potential temperature (i.e. altitude) level in the dome. While the lower dome was mostly only influenced by low-level transport from sources within the cold central and marginal Arctic, for the mid-dome and upper dome during spring it was found that a cold air outbreak over eastern Europe caused intensified northward transport of air from a corridor over western Russia to central Asia. This sector was affected by emissions from gas flaring, industrial activity and wildfires. The development of transport caused rBC concentrations in the second lowest level to gradually increase from 32 to 49 ng m−3. In the third level this caused the initially low rBC concentration to increase from &lt;15 to 150 ng m−3. A shift in rBC mass-mean diameter, from above 200 nm in the lower polar dome dominated by low-level transport to &lt;190 nm at higher levels, may indicate that rBC was affected by wet removal mechanisms preferential to larger particle diameters when lifting processes were involved during transport. The summer polar dome had limited exchange with the mid-latitudes. Air pollution was supplied from sources within the marginal Arctic as well as by long-range transport, but in both cases rBC was largely depleted in absolute and relative concentrations. Near the surface, rBC concentrations were &lt;2 ng m−3, while concentrations increased to &lt;10 ng m−3 towards the upper boundary of the polar dome. The mass mean particle diameter of 132 nm was smaller than in spring; nonetheless the summer mean mass size distribution resembled the spring distribution from higher levels, with depletion of particles &gt;300 nm. Our work provides vertical, spatial and seasonal information of rBC characteristics in the polar dome over the High Canadian Arctic, offering a more extensive dataset for evaluation of chemical transport models and for radiative forcing assessments than those obtained before by other Arctic aircraft campaigns.

A new method to measure real-world respiratory tract deposition of inhaled ambient black carbon

In this study, we present the development of a mobile system to measure real-world total respiratory tract deposition of inhaled ambient black carbon (BC). Such information can be used to supplement the existing knowledge on air pollution-related health effects, especially in the regions where the use of standard methods and intricate instrumentation is limited. The study is divided in two parts. Firstly, we present the design of portable system and methodology to evaluate the exhaled air BC content. We demonstrate that under real-world conditions, the proposed system exhibit negligible particle losses, and can additionally be used to determine the minute ventilation. Secondly, exemplary experimental data from the system is presented. A feasibility study was conducted in the city of La Paz, Bolivia. In a pilot experiment, we found that the cumulative total respiratory tract deposition dose over 1-h commuting trip would result in approximately 2.6 μg of BC. This is up to 5 times lower than the values obtained from conjectural approach (e.g. using physical parameters from previously reported worksheets). Measured total respiratory tract deposited BC fraction varied from 39% to 48% during walking and commuting inside a micro-bus, respectively.To the best of our knowledge, no studies focusing on experimental determination of real-world deposition dose of BC have been performed in developing regions. This can be especially important because the BC mass concentration is significant and determines a large fraction of particle mass concentration. In this work, we propose a potential method, recommendations, as well as the limitations in establishing an easy and relatively cheap way to estimate the respiratory tract deposition of BC.

Influence of cloud microphysical processes on black carbon wet removal, global distributions, and radiative forcing

Abstract. Parameterizations that impact wet removal of black carbon (BC) remain uncertain in global climate models. In this study, we enhance the default wet deposition scheme for BC in the Community Earth System Model (CESM) to (a) add relevant physical processes that were not resolved in the default model and (b) facilitate understanding of the relative importance of various cloud processes on BC distributions. We find that the enhanced scheme greatly improves model performance against HIPPO observations relative to the default scheme. We find that convection scavenging, aerosol activation, ice nucleation, evaporation of rain or snow, and below-cloud scavenging dominate wet deposition of BC. BC conversion rates for processes related to in-cloud water–ice conversion (i.e., riming, the Bergeron process, and evaporation of cloud water sedimentation) are relatively smaller, but have large seasonal variations. We also conduct sensitivity simulations that turn off each cloud process one at a time to quantify the influence of cloud processes on BC distributions and radiative forcing. Convective scavenging is found to have the largest impact on BC concentrations at mid-altitudes over the tropics and even globally. In addition, BC is sensitive to all cloud processes over the Northern Hemisphere at high latitudes. As for BC vertical distributions, convective scavenging greatly influences BC fractions at different altitudes. Suppressing BC droplet activation in clouds mainly decreases the fraction of column BC below 5 km, whereas suppressing BC ice nucleation increases that above 10 km. During wintertime, the Bergeron process also significantly increases BC concentrations at lower altitudes over the Arctic. Our simulation yields a global BC burden of 85 Gg; corresponding direct radiative forcing (DRF) of BC estimated using the Parallel Offline Radiative Transfer (PORT) is 0.13 W m−2, much lower than previous studies. The range of DRF derived from sensitivity simulations is large, 0.09–0.33 W m−2, corresponding to BC burdens varying from 73 to 151 Gg. Due to differences in BC vertical distributions among each sensitivity simulation, fractional changes in DRF (relative to the baseline simulation) are always higher than fractional changes in BC burdens; this occurs because relocating BC in the vertical influences the radiative forcing per BC mass. Our results highlight the influences of cloud microphysical processes on BC concentrations and radiative forcing.

Characterization of aerosol chemical composition from urban pollution in Brazil and its possible impacts on the aerosol hygroscopicity and size distribution

We studied the effect of aerosols inorganic chemical composition on the aerosol hygroscopicity of urban pollution in Brazil, where biofuels have been used in large scale. We applied size segregated inorganic chemical composition analysis using ISORROPIA II model and κ-Köhler theory to determine the hygroscopicity parameter (κ) of submicrometer aerosols measured in São Paulo city. The size dependence of organic and black carbon (BC) mass were estimated by chemical mass balance and mean observed values.Results showed ultrafine mode particles with diameter smaller than 100 nm with a relatively K2SO4 and Na2SO4 large amount inducing further growth by diffusive condensation and coagulation of low-volatile organic compounds. The process could lead to modifications of aerosol size distribution and also to formation of more active Cloud Condensation Nuclei (CCN) due to the formation of aerosols with considerably increase of hygroscopicity (>40%). The contribution from BC can decreases up to 40% of the observed hygroscopicities values of particles around 100 nm in diameter.Moreover, we present a parameterization based on aerosol mass fraction to accurately predict κ derived from data of Aerosol Mass Spectrometer (AMS) collected in urban pollution in Brazil. Results are compared to hygroscopicity derived from observations of the pollution plume downwind Manaus, on the northern region of Brazil. Both cases were analogous indicating that, despite the fact of receiving influences of organic components from the forest, the pollution plume of Manaus shows the same characteristics of hygroscopicity, and can be modeled following the same parameterization.

Vertical distributions of black carbon aerosols over rural areas of the Yangtze River Delta in winter

Based on a field campaign in Shouxian, a rural site on the Yangtze River Delta, China, from December 14, 2016 to January 4, 2017, the vertical profiles of black carbon (BC) and planetary boundary layer (PBL) structures were studied. In total, 58 vertical profiles were obtained, including of the PM2.5, BC mass concentration (mBC) and relevant meteorological parameters. Four profile types were categorized: I: uniform vertical distributions (38%), II: higher values at lower altitudes (29%), III: bimodal distributions with high values near the ground and at higher altitudes (17%), and IV: unimodal distributions with high values at higher altitudes (11%). A further analysis confirmed that all types were mainly influenced by the PBL diurnal evolution and local emissions, while types III and IV were strongly associated with the temperature inversions at low altitudes. The diurnal variations of the BC vertical profiles mainly followed the evolution of the PBL. In the early morning, the average mBC within the PBL (MBL, BC) increased significantly, reaching the highest level in the diurnal cycles, i.e., approximately 13.0 μg m−3. The pollutants were confined to a thin layer <0.2 km above the ground, which contributed to the smoke produced by local residential biomass burning. Around noon, the accumulated BC in the layer was diluted as a result of the development of the PBL. The height of the PBL (HPBL) reached its maximum in the afternoon, with an average of 0.65 km, while MBL, BC dropped to its minimum, with an average of 7.8 μg m−3. As evening approached, the BC produced by local residential biomass burning gradually accumulated near the ground and linearly declined along the standardized height (HS) within the nocturnal boundary layer (NBL). There were large differences in the BC concentration within and above the PBL both in the daytime and at night.

SCOPE11 Method for Estimating Aircraft Black Carbon Mass and Particle Number Emissions.

Black carbon (BC) emissions from aircraft engines lead to an increase in the atmospheric burden of fine particulate matter (PM2.5). Exposure to PM2.5 from sources, including aviation, is associated with an increased risk of premature mortality, and BC suspended in the atmosphere has a warming impact on the climate. BC particles emitted from aircraft also serve as nuclei for contrail ice particles, which are a major component of aviation's climate impact. To facilitate the evaluation of these impacts, we have developed a method to estimate BC mass and number emissions at the engine exit plane, referred to as the Smoke Correlation for Particle Emissions-CAEP11 (SCOPE11). We use a data set consisting of SN-BC mass concentration pairs, collected using certification-compliant measurement systems, to develop a new relationship between smoke number (SN) and BC mass concentration. In addition, we use a complementary data set to estimate measurement system loss correction factors and particle geometric mean diameters to estimate BC number emissions at the engine exit plane. Using this method, we estimate global BC emissions from aircraft landing and takeoff (LTO) operations for 2015 to be 0.74 Gg/year (95% CI = 0.64-0.84) and 2.85 × 1025 particles/year (95% CI = 1.86-4.49 × 1025).

Representativeness and variability of PM2.5 mass concentrations and black carbon near traffic and urban background monitoring stations/Repräsentativität und Variabilität von PM2.5-Massenkonzentrationen und schwarzem Kohlenstoff in der Nähe von Verkehrs- und städtischen Luftgütemessstationen.

Mobile measurements of PM2.5 and black carbon (BC) mass concentrations were performed near regular monitoring stations in order to gain deeper understanding of the drivers of pedestrian exposure to traffic-related air pollution. The following investigations have been done: A) Yearlong measurements in an area around a street canyon approximately 3 km airline distance from the city center of Leipzig showed that the spatial distributions of both pollutants are elevated during wintertime. The patterns of the BC mass concentration, however, consistently showed a strong influence from traffic emissions in the street, while the PM2.5 mass concentration was more dependent on the regional background and less on urban sources. B) Measurements in the city of Dresden near two regular monitoring stations, one at a roadside and one in urban background areas revealed differences between the two in terms of the BC mass concentrations, with slightly higher concentrations at the traffic area. However, no significant differences between the spatial distributions of PM2.5 mass concentrations were observed. The background measurements of the PM2.5 mass concentrations seem to be generally representative for the residential area. C) Measurements near a regular monitoring station located at a junction of the inner-city ring road of Leipzig showed that it is representative of its immediate vicinity in terms of BC mass concentrations. However, the PM2.5 mass concentration varied by a factor 2, reaching the highest levels near in the central tram station about 200 m away. The central tram station seems to significantly influence the PM2.5 mass concentration. These results of the three studies provide a better understanding of the variability of these two parameters in urban areas in Leipzig and Dresden, helping local policy makers to interpret better the measured air pollution.

Aerosol Radiative Forcing Estimation over a Remote High-altitude Location (~4900 masl) near Yala Glacier, Nepal

ABSTRACT In the present study, we estimated the aerosol radiative forcing and heating rates near Yala Glacier, Nepal (28.21°N, 85.61°E; 4900 masl), using in situ black carbon (BC) mass concentration measurements, satellite data sets, and model simulations. The real-time ambient BC mass concentration was continuously measured using an Aethalometer (AE-33) from October 2016 to May 2017. The Optical Properties of Aerosols and Clouds (OPAC) model was used to simulate the aerosol optical properties in conjunction with the in situ measurements and satellite data sets. Outputs from OPAC and the satellite data sets were used as inputs for the Santa Barbara Discrete Ordinate Radiative Transfer Atmospheric Radiative Transfer (SBDART) model to estimate the radiative forcing. The in situ measurements showed that the BC mass concentration peaked during the pre-monsoon season (707.9 ± 541.8 ng m–3), which was corroborated by the higher aerosol optical depth (AOD) values during this season (0.058 ± 0.002). The diurnal cycle of the BC mass concentration exhibited a night-time low and afternoon high, which were influenced by the boundary layer dynamics and valley wind flow pattern. The Concentration Weighted Trajectory (CWT) analysis indicated diverse source regions, including northern Asia, the Indo-Gangetic Plain (IGP), and parts of Nepal and Bangladesh. The Moderate Resolution Imaging Spectroradiometer (MODIS)-derived AOD and Angstrom exponent (AE), and the OPAC-simulated single-scattering albedo (SSA) and asymmetry parameter (AP) over the study site were estimated to be 0.048 ± 0.009 and 1.32 ± 0.01, and 0.938 ± 0.019 and 0.710 ± 0.042, respectively, during the study period. The mean radiative forcing during the study period for the top of the atmosphere, surface and atmosphere were 3.4, –0.5 and 3.9 W m–2, respectively. Higher atmospheric forcing was observed in the pre-monsoon season, leading to changes in the heating rates.

Two-Way Relationship between Aerosols and Fog: A Case Study at IGI Airport, New Delhi

ABSTRACT The frequency and intensity of fog episodes during the winter season has been increasing during the past decade over the megacity of Delhi due to the high pollution load. The role of atmospheric aerosols is very important in the life cycle of fog in the urban areas. This paper presents the results on the variation in aerosol optical properties (scattering and absorption coefficients) and the black carbon (BC) mass concentration during the foggy period in winter (December 2015 to February 2016) at the Indira Gandhi International (IGI) Airport, New Delhi. The interaction between scattering and absorbing aerosols, and fog before, during and after the foggy period has been studied as a typical case. The BC mass concentration, along with the aerosol scattering and absorption coefficients, increased before and during the initial phase of the dense foggy period. However, there was a steep decrease in them after the sustained period of dense fog, which suggests possible scavenging by fog droplets. Also, it was observed that the decrease in ambient temperature and depression temperature (DT) and the increase in relative humidity (RH) played a major role in sustaining the dense fog despite the reduction in aerosol load. The single-scattering albedo (SSA) decreased during the dense fog due to a higher reduction of the scattering aerosols than the absorbing ones. Both the scattering and the absorption coefficients showed a significant correlation with cloud condensation nuclei (CCN).

On the Contribution of Particulate Matter (PM2.5) to Direct Radiative Forcing over Two Urban Environments in India

ABSTRACT Radiative forcing by particulate matter (PM2.5) has been estimated for a period of one year (January–December 2015) over Delhi and Pune (polluted urban metro cities in India). In situ observations of PM2.5 and black carbon (BC) over both the cities were obtained from the ground-based System of Air Quality Forecasting and Research (SAFAR) network of stations. Observations have shown that PM concentrations over Pune had a strong diurnal cycle as compared to Delhi in all the seasons. Also, comparisons of the mode values and seasonal frequency distributions (FDs) over Pune and Delhi showed that pollution levels over Delhi were consistently above National Ambient Air Quality Standards (NAAQS). The mean monthly PM2.5 values ranged from 61.5 to 162.9 over Delhi and from 17.4 to 74.05 over Pune. The BC mass contribution to PM2.5 was found to be 10% to 25% over Pune. However, the contribution of BC to PM2.5 was up to 35% over Delhi. Radiative forcing due to PM2.5 (PRF) over both the sites was estimated using the Optical Properties of Aerosols and Clouds (OPAC) model along with the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model. The PRF in the atmosphere was between +7.73 Wm–2 and +14.51 Wm–2 over Delhi and between +3.12 Wm–2 and +12.15 Wm–2 over Pune. Sensitivity experiments showed that the impact of the increase in the hygroscopicity of the aerosols on the PRF was overshadowed by the net changes in albedo.

Variability of black carbon mass concentrations, sub-micrometer particle number concentrations and size distributions: results of the German Ultrafine Aerosol Network ranging from city street to High Alpine locations

This work reports the first statistical analysis of multi-annual data on tropospheric aerosols from the German Ultrafine Aerosol Network (GUAN). Compared to other networks worldwide, GUAN with 17 measurement locations has the most sites equipped with particle number size distribution (PNSD) and equivalent black carbon (eBC) instruments and the most site categories in Germany ranging from city street/roadside to High Alpine. As we know, the variations of eBC and particle number concentration (PNC) are influenced by several factors such as source, transformation, transport and deposition. The dominant controlling factor for different pollutant parameters might be varied, leading to the different spatio-temporal variations among the measured parameters. Currently, a study of spatio-temporal variations of PNSD and eBC considering the influences of both site categories and spatial scale is still missing. Based on the multi-site dataset of GUAN, the goal of this study is to investigate how pollutant parameters may interfere with spatial characteristics and site categories.

Variability of black carbon mass concentrations, sub-micrometer particle number concentrations and size distributions: results of the German Ultrafine Aerosol Network ranging from city street to High Alpine locations

Variability of black carbon mass concentrations, sub-micrometer particle number concentrations and size distributions: results of the German Ultrafine Aerosol Network ranging from city street to High Alpine locations

Vertical and horizontal distribution of sub-micron aerosol chemical composition and physical characteristics across Northern India, during the pre-monsoon and monsoon seasons

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; The vertical distribution in the physical and chemical properties of submicron aerosol has been characterised across northern India for the first time using airborne in-situ measurements. This study focusses primarily on the Indo-Gangetic Plain, a low-lying area in the north of India which commonly experiences high aerosol mass concentrations prior to the monsoon season. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights in the region during the 2016 pre-monsoon (11&lt;sup&gt;th&lt;/sup&gt; and 12&lt;sup&gt;th&lt;/sup&gt; June) and monsoon (30&lt;sup&gt;th&lt;/sup&gt; June to 11&lt;sup&gt;th&lt;/sup&gt; July) seasons.&lt;/p&gt; &lt;p&gt; Inside the Indo-Gangetic Plain boundary layer, organic matter dominated the submicron aerosol mass (43&amp;amp;thinsp;%) followed by sulphate (29&amp;amp;thinsp;%), ammonium (14&amp;amp;thinsp;%), nitrate (7&amp;amp;thinsp;%) and black carbon (7&amp;amp;thinsp;%). However, outside the Indo-Gangetic Plain, sulphate was the dominant species contributing 44&amp;amp;thinsp;% to the total submicron aerosol mass in the boundary layer, followed by organic matter (30&amp;amp;thinsp;%), ammonium (14&amp;amp;thinsp;%), nitrate (6&amp;amp;thinsp;%) and black carbon (6&amp;amp;thinsp;%). Chlorine mass concentrations were negligible throughout the campaign. Black carbon mass concentrations were higher inside the Indo-Gangetic Plain (2&amp;amp;thinsp;µg/m&lt;sup&gt;3&lt;/sup&gt; std) compared to outside (1&amp;amp;thinsp;µg/m&lt;sup&gt;3&lt;/sup&gt; std). Nitrate appeared to be controlled by thermodynamic processes, with increased mass concentration in conditions of lower temperature and higher relative humidity. Increased mass and number concentrations were observed inside the Indo-Gangetic Plain and the aerosol was more absorbing in this region, whereas outside the Indo-Gangetic Plain the aerosol was larger in size and more scattering in nature, suggesting greater dust presence especially in northwest India. The aerosol composition remained largely similar as the monsoon season progressed, but the total aerosol mass concentrations decreased by ~&amp;amp;thinsp;50&amp;amp;thinsp;% as the rainfall arrived; the pre-monsoon average total mass concentration was 30&amp;amp;thinsp;µg/m&lt;sup&gt;3&lt;/sup&gt; std compared to a monsoon average total mass concentration of 10&amp;amp;ndash;20&amp;amp;thinsp;µg/m&lt;sup&gt;3&lt;/sup&gt; std. However, this mass concentration decrease was less noteworthy (~&amp;amp;thinsp;20&amp;amp;ndash;30&amp;amp;thinsp;%) over the Indo-Gangetic Plain, likely due to the strength of emission sources in this region. Decreases occurred in coarse mode aerosol, with the fine mode fraction increasing with monsoon arrival. In the aerosol vertical profile, inside the Indo-Gangetic Plain during the pre-monsoon, organic aerosol and absorbing aerosol species dominated in the lower atmosphere (&lt;&amp;amp;thinsp;1.5&amp;amp;thinsp;km) with sulphate, dust and other scattering aerosol species enhanced in an elevated aerosol layer above 1.5&amp;amp;thinsp;km with maximum aerosol height ~&amp;amp;thinsp;6&amp;amp;thinsp;km. As the monsoon progressed into this region, the elevated aerosol layer diminished, the aerosol maximum height reduced to ~&amp;amp;thinsp;2&amp;amp;thinsp;km and the total mass concentrations decreased by ~&amp;amp;thinsp;50&amp;amp;thinsp;%. The dust and sulphate-dominated aerosol layer aloft was removed upon monsoon arrival, highlighted by an increase in fine mode fraction throughout the profile.&lt;/p&gt;

Estimating Source Region Influences on Black Carbon Abundance, Microphysics, and Radiative Effect Observed Over South Korea

AbstractEast Asia is the strongest global source region for anthropogenic black carbon (BC), the most important light‐absorbing aerosol contributing to direct radiative climate forcing. To provide extended observational constraints on regional BC distributions and impacts, in situ measurements of BC were obtained with a single particle soot photometer during the May/June 2016 Korean‐United States Air Quality aircraft campaign (KORUS‐AQ) in South Korea. Unique chemical tracer relationships were associated with BC sourced from different regions. The extent and variability in vertical BC mass burden for 48 profiles over a single site near Seoul were investigated using back trajectory and chemical tracer analysis. Meteorologically driven changes in transport influenced the relative importance of different source regions, impacting observed BC loadings at all altitudes. Internal mixing and size distributions of BC further demonstrated dependence on source region: BC attributed to China had a larger mass median diameter (180 ± 13 nm) than BC attributed to South Korea (152 ± 25 nm), and BC associated with long‐range transport was less thickly coated (60 ± 4 nm) than that sourced from South Korea (75 ± 16 nm). The column BC direct radiative effect at the top of the atmosphere was estimated to be W/m2, with average values for different meteorological periods varying by a factor of 2 due to changes in the BC vertical profile. During the campaign, BC sourced from South Korea (≤ 31%), China (22%), and Russia (14%) were the most significant single‐region contributors to the column direct radiative effect.

Characterizing black carbon aerosols in relation to atmospheric boundary layer height during wet removal processes over a semi urban location

Black Carbon (BC) mass concentration has been analysed during rainy and non-rainy days of Northeast (NE) Monsoon months of the years 2015 and 2017 over a semi-urban environment near Chennai (12.81 N, 80.03 E), located on the east coast of India. BC, measured using an Aethalometer (AE-31) has been related to the atmospheric Boundary Layer Height (BLH) obtained from the ERA Interim Reanalysis data during rainy and non-rainy days on monthly mean basis to understand the wet removal of BC over the study location. The study reveals that BLH has a profound effect on the BC concentration on rainy days and non rainy days. It is found that the BC concentration in the night time is lower on rainy days compared to non rainy days owing to wash out on rainy days and the BLH remaining nearly the same on rainy and non rainy days. On the other hand, in the daytime it is found that the BC concentration remains nearly the same on rainy and non rainy days whereas the BLH is lower on rainy days compared to non rainy days. This reveals that in daytime lower boundary layer heights compensate for the wet removal effect on BC concentration on rainy days. A quantitative relation is found between the product of BC and BLH during rainy and non-rainy days which indicates the extent of redistribution of BC during non-rainy days when compared to the rainy days. In the process of analysing BC during the wet removal processes, the basic features of BC such as its mean diurnal variations, transport pathways, local sources and its relation with relative humidity were also reported.

Factors controlling the long-term (2009–2015) trend of PM2.5 and black carbon aerosols at eastern Himalaya, India

A first-ever long-term (2009–2015) study on the fine particulate matter (PM2.5) and black carbon (BC) aerosol were conducted over Himalaya in order to investigate the characteristics, temporal variations and the important factors regulating the long-term trend. The study was conducted over a high altitude station, Darjeeling (27°01′N, 88°15′E, 2200 m asl) representing a typical high altitude urban atmosphere at eastern Himalaya in India. The average concentrations of PM2.5 and BC over a period of seven years were 25.2 ± 5.6 μg m−3 (ranging between 2.2 and 220.4 μg m−3) and 3.4 ± 0.7 μg m−3 (0.4 to 15.6 μg m−3) respectively. We observed decreasing trends in both PM2.5 (49% at a rate of 170 ng m−3 month−1) and BC (34% at the rate of 20 ng m−3 month−1) mass concentration over this region from 2009 to 2015. We extensively studied the impact of micrometeorological parameters on the long-term trend in PM2.5 and BC through the correlation analysis. The significant changes in boundary layer dynamics over this region played a major role in the decreasing trend of aerosols. The concentration weighted trajectory analysis revealed that the important contributory long-distant source regions for PM2.5 and BC over eastern Himalaya were Indo Gangetic Plane and Nepal. The contributions from these regions were found to be decreased significantly from 2009 to 2015. Investigations on the fire counts associated with the forest fire, and open burning activities through the satellite observations revealed that the decreasing trend in PM2.5 and BC over eastern Himalaya is well correlated to the decreasing trend in the fire counts over IGP and Nepal. We also explored that the changes and up gradation of the domestic fuel at the Indo Gangetic Plane regions in recent years not only improved the regional air quality but also affected the atmospheric environment over the eastern part of Himalaya.