Black Carbon Aerosol Mass Concentration Research Articles

Observations on the decadal variability of aerosol in eastern Himalayan foothills: Evidence of an anthropologically induced positive shift

The decadal variability of direct radiative effects of aerosols is investigated at Dibrugarh, a site in northeast India (NEI) at the eastern Himalayan foothills, primarily using multi-wavelength solar radiometer measurements spanning from October 2001 to February 2020. The ground-based aerosol observations are combined with satellite remote sensing, reanalysis data, and model simulations to study the change in atmospheric particle loading over the region. Observations indicate a statistically significant increase (∼0.015 yr−1) in Aerosol Optical Depth (AOD) during the last two decades in line with an increase in human activity. As compared to 2001–2007 (we call it as Stage I), the aerosol burden has grown rapidly during 2008 until 2020 (Stage II). AOD at 500 nm is found to increase by ∼40% from Stage I to Stage II, resulting in an increase in the aerosol direct radiative forcing (DRF) at the top of the atmosphere (TOA) by ∼43% during stage II (∼−16.0 W m-2), from the base value of −11.2 W m−2 in Stage I. Decreasing biomass burning activities, black carbon aerosol mass concentration, and high sulfate and organic aerosols are the primary factors responsible for the trend in TOA cooling by −0.46 W m−2 yr−1. This is further aided by the decrease in rainfall over NEI. MERRA-2 data analysis shows a similar enhancements in aerosol load over the entire NEI and the adjacent highly polluted Indo-Gangetic Plains (IGP). A similar feature is seen over the IGP, primarily driven by anthropogenic emissions, but precedes that in NEI by about a year. A simulation of the regional climate model (RegCM) over the south Asian domain quantifies the contribution of aerosol loading over NEI due to the aerosols carried from the IGP. In the highest aerosol loading period, about 12–30% of the aerosols, equivalent to 15–30% of atmospheric warming, are transported from the IGP to the NEI.

Black carbon aerosol number and mass concentration measurements by picosecond short-range elastic backscatter lidar

Black carbon aerosol emissions are recognized as contributors to global warming and air pollution. There remains, however, a lack of techniques to remotely measure black carbon aerosol particles with high range and time resolution. This article presents a direct and contact-free remote technique to estimate the black carbon aerosol number and mass concentration at a few meters from the emission source. This is done using the Colibri instrument based on a novel technique, referred to here as Picosecond Short-Range Elastic Backscatter Lidar (PSR-EBL). To address the complexity of retrieving lidar products at short measurement ranges, we apply a forward inversion method featuring radiometric lidar calibration. Our method is based on an extension of a well-established light-scattering model, the Rayleigh–Debye–Gans for Fractal-Aggregates (RDG-FA) theory, which computes an analytical expression of lidar parameters. These parameters are the backscattering cross-sections and the lidar ratio for black carbon fractal aggregates. Using a small-scale Jet A-1 kerosene pool fire, we demonstrate the ability of the technique to quantify the aerosol number and mass concentration with centimetre range-resolution and millisecond time-resolution.

Phase-Resolved Lockdown Features of Pollution Parameters Over an Urban and Adjoining Rural Region During COVID-19

In this study, we investigate the temporal variations in columnar aerosol pollutants and their possible association with the simultaneously measured black carbon (BC) aerosol mass concentration and associated biomass burning (BB) over urban (Delhi) and rural (Panchgaon) sites during the lockdown phases of the COVID-19 pandemic. We also show the impact of lockdown measures on boundary layer ozone and its primary precursors, NO2, and water vapor (H2O), potent greenhouse gases that destroy protective ozone. For this purpose, we used multiple datasets, namely, black carbon (BC) aerosol mass concentration and biomass burning (BB) aerosols using an aethalometer at Amity University Haryana (AUH), Panchgaon, India, and satellite retrievals from NASA’s MODIS and OMI at both the stations. The analysis was conducted during the pre-lockdown period (1–25 March), lockdown 1st phase (25 March–14 April), lockdown 2nd phase (15 April–3 May), lockdown 3rd phase (4–17 May), lockdown 4th phase (18–31 May), and post-lockdown (1–30 June) period in 2020. Our diagnostic analysis shows a substantial reduction in AOD (Delhi: −20% to −80%, Panchgaon: −20% to −80%) and NO2 (Delhi: −10% to −42.03%, Panchgaon −10% to −46.54%) in comparison with climatology (2010–2019) during all four phases of lockdown. The reduction in AOD is attributed to lockdown measures and less transport of dust from west Asia than climatology. Despite a reduction in NO2, there is an increase in the ozone amount (Delhi: 1% to 8% and Panchgaon: 1% to 10%) during lockdown I, II, and III phases. The observed enhancement in ozone may be resultant from the complex photochemical processes that involve the presence of NO2, CO, volatile organic compounds (VOCs), and water vapor. The reduction in AOD and NO2 and enhancement in ozone are stronger at the rural site, Panchgaon than that at the urban site, Delhi.

Characteristics and Extent of Particulate Matter Emissions of a Ropeway Public Mobility System in the City Center of Perugia (Central Italy)

Minimetrò (MM) is a ropeway public mobility system that has been in operation in the city of Perugia for about ten years to integrate with urban mobility and lighten vehicular traffic in the historic city center. The purpose of this work was to evaluate the impact of MM as a source of pollutants in the urban context, and the exposure of people in the cabins and the platforms along the MM line. These topics have been investigated by means of intensive measurement and sampling campaigns performed in February and June 2015 on three specific sites of the MM line representative of different sources and levels of urban pollution. Stationary and dynamic measurements of particle size distribution, nanoparticle and black carbon aerosol number and mass concentrations measurements were performed by means of different bench and portable instruments. Aerosol sampling was carried out using low volume and high-volume aerosol samplers, and the samples nalysed by off-line methods. Results show that MM is a considerable source of atmospheric particulate matter having characteristics very similar to those of the common urban road dust in Perugia. In the lack of clear indications on road dust effect, the contribution of MM to the aerosol in Perugia cannot be neglected.

Modeling the smoky troposphere of the southeast Atlantic: a comparison to ORACLES airborne observations from September of 2016

Abstract. In the southeast Atlantic, well-defined smoke plumes from Africa advect over marine boundary layer cloud decks; both are most extensive around September, when most of the smoke resides in the free troposphere. A framework is put forth for evaluating the performance of a range of global and regional atmospheric composition models against observations made during the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) airborne mission in September 2016. A strength of the comparison is a focus on the spatial distribution of a wider range of aerosol composition and optical properties than has been done previously. The sparse airborne observations are aggregated into approximately 2∘ grid boxes and into three vertical layers: 3–6 km, the layer from cloud top to 3 km, and the cloud-topped marine boundary layer. Simulated aerosol extensive properties suggest that the flight-day observations are reasonably representative of the regional monthly average, with systematic deviations of 30 % or less. Evaluation against observations indicates that all models have strengths and weaknesses, and there is no single model that is superior to all the others in all metrics evaluated. Whereas all six models typically place the top of the smoke layer within 0–500 m of the airborne lidar observations, the models tend to place the smoke layer bottom 300–1400 m lower than the observations. A spatial pattern emerges, in which most models underestimate the mean of most smoke quantities (black carbon, extinction, carbon monoxide) on the diagonal corridor between 16∘ S, 6∘ E, and 10∘ S, 0∘ E, in the 3–6 km layer, and overestimate them further south, closer to the coast, where less aerosol is present. Model representations of the above-cloud aerosol optical depth differ more widely. Most models overestimate the organic aerosol mass concentrations relative to those of black carbon, and with less skill, indicating model uncertainties in secondary organic aerosol processes. Regional-mean free-tropospheric model ambient single scattering albedos vary widely, between 0.83 and 0.93 compared with in situ dry measurements centered at 0.86, despite minimal impact of humidification on particulate scattering. The modeled ratios of the particulate extinction to the sum of the black carbon and organic aerosol mass concentrations (a mass extinction efficiency proxy) are typically too low and vary too little spatially, with significant inter-model differences. Most models overestimate the carbonaceous mass within the offshore boundary layer. Overall, the diversity in the model biases suggests that different model processes are responsible. The wide range of model optical properties requires further scrutiny because of their importance for radiative effect estimates.

Analysis of aerosol optical properties in a Lanzhou suburb of China

In order to accurately identify feature layer and monitor the spatial and temporal distribution of pollutants, the inversion method of lidar measurement based on multiscale algorithm is proposed in this paper. The detection of clouds, aerosols and dust layers using a modified retrieval algorithm for a dual-wavelength lidar is presented at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Moreover, the aerosol optical depth calculated from the Klett-Fernald algorithm obviously excludes the influence of clouds. Two cases were presented to demonstrate that the modified algorithm can capture low-clouds and dust layers well. The aerosol optical properties including aerosol optical depth (AOD), effective radius, depolarization ratio and black carbon aerosol mass concentration are analysed in terms of their monthly and seasonal variations. It is shown that the maximum of AOD, depolarization ratio and effective radius were found in spring (0.42 ± 0.35, 0.17 ± 0.1, 0.63 ± 0.24 μm) and the minimums were found in summer and autumn. The black carbon aerosol mass concentration varies significantly throughout year, with the maximum value in winter (2.35 ± 1.56 μg m−3) and a secondary maximum in autumn (1.93 ± 1.28 μg m−3), a minimum (1.03 ± 0.76 μg m−3) in spring. The vertical distribution of extinction coefficient has a peak near 1 km (0.1 km−1). The depolarization ratio vertically distributes at approximately 0.15. In general, pollution is more serious in spring and winter at SACOL, the former pollutants are coarse-mode non-spherical dust particles which originate from the Taklimakan Desert and the Gobi Desert, and the latter are fine mode spherical black carbon aerosols and coarse-mode non-spherical dust aerosols which are the results of both local combustion and long-distance transport. The dust particles existed high-altitude transport in spring and winter at SACOL.

Evaluation of spatial and temporal heterogeneity of black carbon aerosol mass concentration over India using three year measurements from IMD BC observation network

Extensive measurements of equivalent black carbon (EBC) aerosol mass concentration at fifteen stations of India Meteorological Department (IMD) BC observation network during the period 2016–2018 are used to study the spatial and temporal heterogeneity over India. The sampling sites represent different geographical region of India. Spatial distribution shows higher values of EBC over stations of north India and IGP. Highest annual mean EBC mass concentration during study period was reported at two mega cities New Delhi (13,575 ± 8401 ng/m3) followed by Kolkata (12,082 ± 6850 ng/m3) whereas lowest mean concentration was at Ranichauri (1737 ± 884 ng/m3) followed by Bhuj (2021 ± 1471 ng/m3). Stations located in coastal region of south India reported low concentration of EBC. In order to find out the quantitative contribution of biomass burning (EBCBB) and fossil fuel (EBCFF) in total mass concentration of EBC, source apportionment study has been carried out using Aethalometer model. The EBCFF is the dominant contributor to EBC mass concentration at all the sites in every season, while the highest seasonal biomass burning mass contribution (37%) was observed in the winter at a background site Ranichauri. Maximum concentration of EBCBB was observed at Srinagar (2671 ng/m3) where as EBCFF was maximum in Delhi (11,074 ng/m3). Seasonal and diurnal variation studies have also been carried out for all the stations. The EBC mass concentrations exhibited strong seasonality, with the highest values occurring in postmonsoon/winter and the lowest in monsoon season. The higher EBC concentration in postmonsoon/winter seasons was attributed to the increased use of fuel in seasonal emission sources, domestic heating and stagnant meteorological conditions, whereas the low levels in monsoon season were related to the precipitation scavenging. Maximum concentration of EBC (22,409 ± 10,510 ng/m3) was observed in winter season over Kolkata. Our study finds high spatial heterogeneity in EBC concentrations across the study area.

Black carbon aerosol quantification over north-west Himalayas: Seasonal heterogeneity, source apportionment and radiative forcing

Continuous measurements of Black Carbon (BC) aerosol mass concentrations were carried at Dehradun (30.33°N, 78.04°E, 700 m amsl), a semi-urban site in the foothills of north-westHimalayas, India during January 2011–December 2017. We reported both the BC seasonal variations as well as mass concentrations from fossil fuel combustion (BCff) and biomass burning (BCbb) sources. Annual mean BC exhibited a strong seasonal variability with maxima during winter (4.86 ± 0.78 μg m−3) followed by autumn (4.18 ± 0.54 μg m−3), spring (3.93 ± 0.75 μg m−3) and minima during summer (2.41 ± 0.66 μg m−3). Annual averaged BC mass concentrations were 3.85 ± 1.16 μg m−3 varying from 3.29 to 4.37 μg m−3 whereas BCff and BCbb ranged from 0.11 to 7.12 μg m−3 and 0.13–3.6 μg m−3. The percentage contributions from BCff and BCbb to total BC are 66% and 34% respectively, indicating relatively higher contribution from biomass burning as compared to other locations in India. This is explained using potential source contribution function (PSCF) and concentration weighted trajectories (CWT) analysis which reveals the potential sources of BC originating from the north-west and eastern parts of IGP and the western part of the Himalayas that are mostly crop residue burning and forest fire regions in India. The annual mean ARF at top-of-atmosphere (TOA), at surface (SUR), and within the atmosphere (ATM) were found to be −14.84 Wm−2, −43.41 Wm−2, and +28.57 Wm−2 respectively. To understand the impact of columnar aerosol burden on ARF, the radiative forcing efficiency (ARFE) was estimated and averaged values were −31.81, −91.63 and 59.82 Wm−2 τ−1 for TOA, SUR and ATM respectively. The high ARFE within the atmosphere indicates the dominance of absorbing aerosol (BC and dust) over Northwest Himalayas.

Retrieval of black carbon aerosol surface concentration using satellite remote sensing observations

As an important part of the anthropogenic aerosol, Black Carbon (BC) aerosols in the atmospheric environment have strong impacts on climate change. Recently, most remote sensing studies on aerosol components detection are limited to the inversion of aerosol optical properties, integration of chemistry models or in situ observations. In this paper, an algorithm based on Effective Medium Approximations (EMA) and statistically optimized aerosol inversion algorithm was integrated for retrieving the surface mass concentration of BC aerosols from satellite signals. The sensitivity analyses for the developed forward model proved that the volume fraction of vertical BC is sensitive to the satellite observations and significantly improved especially over bright surface targets or under polluted atmospheric conditions. By updating the forward model and retrieved parameters of the statistically optimized inversion algorithm, three cases of high aerosol loading days were retrieved from Polarization and Anisotropy of Reflectance for Atmospheric Sciences Coupled with Observations from a LiDAR (PARASOL) measurements, which shows a significant ability of BC aerosol detection. Additionally, the validation and closure studies of BC concentration retrievals also indicates an encouraging consistency with correlation (R) of 0.71, mean bias of 3.55, and root-mean-square error (RMSE) of 3.75 when compared against the in-situ observations over South Asia. The accuracy of the retrievals also demonstrates different trends under different levels of aerosol loadings, which shows a higher accuracy in biomass burning seasons (R = 0.75, RMSE = 4.04, Bias = 3.27) while exaggerates the results in the case of clear conditions (R = 0.47, RMSE = 4.83, Bias = 4.00). Finally, the uncertainties of three assumptions, including proposing uniform vertical profile for BC, neglecting light-absorbing aerosols and using spherical EMA models were discussed in our manuscript. The maximum standard deviations caused by these uncertainties on low BC aerosol volume fractions (fBC < 1%) are 0.8%, 0.35% and 0.2% while these deviations will change to 0.25%, 0.05% and 1.5% respectively under higher BC fractions (fBC > 5%). This conclusion confirmed that the proposed algorithm for BC surface concentration retrieval extends the application of satellite remote sensing in monitoring the extreme biomass burning pollution.

Spatial, temporal and source study of black carbon in the atmospheric aerosols over different altitude regions in Southern India

Ambient equivalent black carbon (EBC) aerosol mass concentration is regularly observed over a period of 2 years (June 2014 to May 2016) at Kodaikanal, a high-altitude and Madurai, a semi-arid location to study its spatial and temporal characteristics and its sources. The diurnal variation of EBC had two peaks, early morning sharp peak that occurred between 06:00 and 09:00 h (LT) almost an hour after the local sunrise and the evening broad peak that occurred between 19:00 to 22:00 h (LT), while in Kodaikanal late afternoon peaks showed maximum contribution. The difference in the sunshine hours with respect to seasons also caused an effect on the EBC concentration. The mean seasonal values of EBC over Kodaikanal are 2.58 ± 0.15 μg m−3, 1.98 ± 0.19 μg m−3, 1.01 ± 0.19 μg m−3 and 2.48 ± 0.15 μg m−3 and over Madurai 8.97 ± 2.34 μg m−3, 4.69 ± 2.14 μg m−3, 6.70 ± 3.83 μg m−3 and 3.34 ± 2.53 μg m−3 during winter, summer, monsoon and post-monsoon seasons, respectively. The effects of meteorological parameters on EBC at the two stations are investigated and it is found that wind speed and rainfall plays a major role. Source identification is done by calculating absorption Angstrom exponent (α). The absorption Angstrom exponent values ranged from 0.99 to 1.15 with the average value of 1.05 for Madurai and a range from 0.54 to 1.92 with an average value of 1.43 for Kodaikanal, indicating that the major sources of EBC on the study site are from biomass burning and fossil fuel burning sources.

Black carbon aerosol mass concentration, absorption and single scattering albedo from single and dual spot aethalometers: Radiative implications

Black carbon (BC) is a primary aerosol emitted directly into the atmosphere from incomplete combustion. It absorbs incoming solar radiation and outgoing terrestrial radiation, which has significant implications to aerosol radiative forcing. Aethalometer employs optical attenuation technique to measure real-time BC mass concentrations. BC mass concentration measured using a single spot aethalometer (AE31) can be significantly uncertain due to filter loading effect. A modified version of AE31, namely, a dual spot aethalometer (AE33), uses a real-time loading effect compensation algorithm and measures BC mass concentrations. BC mass concentrations measured using single and dual spot aethalometers over an urban location are analysed. BC mass concentration from AE33 is higher (11%) than BC measured by post processed loading effect compensated AE31 data. Daily averaged BC mass concentration measured by AE31 and AE33 shows a very good linear agreement (coefficient of determination (0.98), and a small zero offset (0.22)). Aerosol absorption coefficients show an average difference of 28.5% between the two aethalometers. Aerosol absorption coefficient is utilised with nephelometer measured aerosol scattering coefficients to compute single scattering albedo (SSA). SSA (550 nm) estimated from the AE33 is always higher (∼ 8%) than AE31. Estimates of aerosol radiative forcing show that when SSA changes from 0.65 to 0.70 over urban regions the atmospheric warming changes by 10%, while when SSA changes from 0.85 to 0.90 the atmospheric warming changes by 25%. This study highlights the non-linear relation between SSA and aerosol forcing, and reveals how crucial it is to determine single scattering albedo accurately in order to reduce the uncertainty in aerosol radiative forcing estimate.

Seasonal characteristics of black carbon aerosol mass concentrations and influence of meteorology, New Delhi (India)

This study investigates seasonal variability in black carbon (BC) aerosol mass concentrations at New Delhi, a monsoon-influenced urban agglomeration located at the edge of the Indo-Gangetic Plain and the Aravalli hills. Incessant measurement of BC has been carried out using Aethalometer AE-42 with the PM2.5 selective inlet. The BC concentrations show significant seasonal, diurnal and hourly variations. The hourly concentrations show a persistent peak distribution during the observation period with different magnitudes. There are two sharp peaks; first one in the morning between 8:00 and 11:00h and the second one at night between 21:00 to 23:00h. The morning high concentration peaks are more pronounced in all the observed months. The hourly and weekly analysis of BC concentrations indicates a significant contribution of vehicle emission, showing a definite pattern with the volume of traffic flow. Though, seasonal variation reveals that the local meteorological conditions directly influence it. Mean BC concentrations during summer; monsoon and post-monsoon seasons are 6.33, 4.95 and 17.4μg mˉ3, respectively. The correlation coefficient of BC concentrations with temperature and relative humidity (RH) indicates that temperature and RH influence the boundary layer dynamics which in turn result into diurnal and seasonal variability in BC concentrations at the ground level.

Black carbon aerosols in a tropical semi-urban coastal environment: Effects of boundary layer dynamics and long range transport

Regular measurements of Black Carbon (BC) aerosol mass concentration have been carried out since March 2011 at a tropical location (12.81°N, 80.03°E) adjoining the mega city, Chennai, on the east coast of India for the first time. As this region is influenced by both the South West and North East monsoons, the BC observations at this site assume importance in understanding the overall BC distribution over India. The data collected until August 2012 has been examined for the general and regionally distinctive features. Spectral absorption characteristics reveal that the BC is mainly from fossil fuel based emissions. The BC concentration shows significant diurnal variation only in the North East monsoon and winter seasons with night time concentration considerably higher than the day time concentration. In the other seasons the day–night contrast in BC is not significant. Seasonal variation is rather subdued with a broad maximum during the Northeast monsoon and winter months and a minimum during the southwest monsoon months. The observed diurnal and seasonal variations are examined in the light of local Atmospheric Boundary Layer dynamics and long range transport. For the first time, an inverse relationship has been established between BC and ABL height on a quantitative basis. A distinctive feature of the region is that in all the seasons transport pathways have long continental overpasses which could lead to the suppressed seasonal variation. It is found that the BC over this region shows distinct diurnal and seasonal features compared to those reported for other coastal and inland regions in India.

Comparison between urban aerosol products retrieved from collocated Cimel and Prede Sun/sky radiometers at Pune, India

To comprehend the characteristics of heterogeneous aerosols, apart from some thematic multi-institutional, multi-platform and multi-parameter campaigns conducted at several places over the globe, presently two major ground-based networks, involving Cimel (AERONET) and Prede (SKYNET) Sun/sky photometers/radiometers have been in progress. In this paper, we report the results of a study that has been undertaken to compare the performance and data products of Cimel and Prede instruments, which were operated concurrently for a period of about 2 years, at the Indian Institute of Tropical Meteorology, Pune, India. The results show a good agreement in the direct Sun observations (aerosol optical depth). The results are also substantiated by making comparison with surface-level black carbon aerosol mass concentration, apart from comparison of other parameters. With regard to the retrieved products such as aerosol size distribution, Prede shows more or less equal concentration of fine mode and relatively more concentration of coarse mode aerosol as compared to those measured by the Cimel. Moreover, the single scattering albedo values measured by the Prede overestimate those observed by the Cimel. These deviations are found to be primarily due to the nature of aerosol loading (turbidity) in the sensing region which is sensitive to the data retrieval techniques including model assumptions employed in both networks. The results of the present study are found useful for multidimensional mapping of aerosol characteristics by integrating the products from both AERONET and SKYNET monitoring stations and thereby help understanding better the impact of aerosols on climate.

Black carbon aerosol variations over Patiala city, Punjab, India—A study during agriculture crop residue burning period using ground measurements and satellite data

In the present study, we have analyzed the variations in black carbon (BC) aerosol mass concentration over Patiala city, Punjab, India, during October/November-2008 associated with agriculture crop residue burning activities. BC mass concentration, observed to be very high (above 20μgm−3) on certain days during November-2008, was closely associated with intensive agriculture crop residue burning practices over the region. Higher values (>1.0) of ground-measured aerosol optical depth (AOD) together with increase (>1.2) in angstrom exponent (α) values suggested dominance of fine mode aerosols over the region. Satellite observations clearly define the fire spot areas and the enhanced aerosol burden over the region. BC absorption coefficient calculated from seven channels aethalometer exhibits a pronounced diurnal variation with higher values during early morning and evening hours and lower during noon and early afternoon associated with biomass-burning activities and boundary-layer dynamics over the region.

Strong radiative heating due to wintertime black carbon aerosols in the Brahmaputra River Valley

The Brahmaputra River Valley (BRV) of Southeast Asia recently has been experiencing extreme regional climate change. A week‐long study using a micro‐Aethalometer was conducted during January–February 2011 to measure black carbon (BC) aerosol mass concentrations in Guwahati (India), the largest city in the BRV region. Daily median values of BC mass concentration were 9–41μgm−3, with maxima over 50 μgm−3during evenings and early mornings. Median BC concentrations were higher than in mega cities of India and China, and significantly higher than in urban locations of Europe and USA. The corresponding mean cloud‐free aerosol radiative forcing is −63.4 Wm−2 at the surface and +11.1 Wm−2at the top of the atmosphere with the difference giving the net atmospheric BC solar absorption, which translates to a lower atmospheric heating rate of ∼2 K/d. Potential regional climatic impacts associated with large surface cooling and high lower‐atmospheric heating are discussed.

Analysis of Diurnal and Seasonal Behavior of Surface Ozone and Its Precursors (NOx) at a Semi-Arid Rural Site in Southern India

Surface measurements of O3, NO, NO2 and NOx have been made over a semi-arid rural site, Anantapur (14.62°N; 77.65°E; 331 m asl) in southern India, during January-December 2010. The highest monthly mean O3 concentration was observed in April (56.1 ± 9.9 ppbv) and the lowest in August (28.5 ± 7.4), with an annual mean of 40.7 ± 8.7 ppbv for the observation period. Seasonal variations in O3 concentrations were the highest during the summer (70.2 ± 6.9 ppbv), and lowest during the monsoon season (20.0 ± 4.7 ppbv), with an annual mean of 40.7 ± 8.7 ppbv. In contrast, higher NOx values appeared in the winter (12.8 ± 0.8 ppbv) followed by the summer season (10.9 ± 0.7 ppbv), while lower values appeared in the monsoon season (3.7 ± 0.5 ppbv). The results for O3, NO and NO2 indicate that the level of oxidant concentration ([OX] = NO2 + O3) at a given location is the sum of NOx-independent “regional contribution” (background level of O3) and linearly NOx-dependent “local contribution”. The O3 concentration shows a significant positive correlation with temperature, and a negative correlation with both wind speed and relative humidity. In contrast, NOx have a significant positive correlation with humidity and wind speed, and negative correlation with temperature. The slope between [BC] and [O3] suggests that every 1 μg/m3 increase in black carbon aerosol mass concentration causes a reduction of 4.7 μg/m3 in the surface ozone concentration. A comparative study using satellite data shows that annual mean values of tropospheric ozone contributes 12% of total ozone, while near surface ozone contributes 82% of tropospheric ozone. The monthly mean variation of tropospheric ozone is similar to that tropospheric NO2, with a correlation coefficient of +0.80.

Anthropogenic impact on the temporal variations of black carbon and surface aerosol mass concentrations at a tropical semi-arid station in southeastern region of India

Collocated measurements of black carbon (BC) and composite aerosol mass concentrations were continuously monitored at Anantapur (14.62°N, 77.65°E, 331 m asl), a tropical semi-arid station in southeastern region of India, using Aethalometer and a ten-channel Quartz Crystal Microbalance (QCM) cascade impactor, respectively during August 2009–July 2010. Diurnal and seasonal variations of BC and near surface aerosols in relation to changes in the regional meteorological conditions, frequency distribution of BC for different seasons, week days and weekend days effect on BC concentration and size distributions of near surface aerosols were observed. Also, using the HYSPLIT model, back-trajectories were studied to assess the sources for transported particles. Diurnal variation of BC showed two peaks, one in the morning and another in the evening, which were mostly related to the daily changes in the local boundary layer. BC concentrations were maximum during the winter (4.76 ± 0.97 μg m −3), and minimum concentrations were observed in the monsoon (1.44 ± 0.26 μg m −3). The total mass concentration exhibits a high value in the summer (48.89 ± 2.57 μg m −3) and it remains low in the monsoon (30.33 ± 1.65 μg m −3) period. The maximum BC mass fraction was found to be 9.4% in the winter and a minimum of 4.6% in the monsoon.

Aerosol climatology over an urban site, Tirupati (India) derived from columnar and surface measurements: First time results obtained from a 30-day campaign

In the present study, collocated and simultaneous data on spectral aerosol optical depth (AOD), mass concentration and size distribution of near-surface composite aerosols and black carbon aerosol mass concentrations were obtained from Microtops-II Sunphotometer, Quartz Crystal Microbalance (QCM) and Aethalometer, respectively, over an urban location, Tirupati (India) in the month of May 2009. The mean AOD at 500 nm and Ångström parameters ( α, β) during this period were obtained as 0.64±0.13 and 0.89±0.24, 0.36±0.10, respectively. The total surface aerosol mass concentration varied from 13 to 60 μg m −3 out of which coarse mode dominated by 39%. The mean value of total mass concentration of aerosols was 23.80±0.25 μg m −3. The Ångström wavelength exponent ( α) showed a positive correlation of 0.60 with the near-surface fine-mode fraction. The total mass concentration showed positive and negative correlations of 0.72 and 0.68 with air temperature and relative humidity, respectively. Along with this, the diurnal variation of black carbon aerosol concentration varied from 2 to 14 μg m −3 and observed prominently a sharp fumigation peak at around 07:00–09:00 h and the nocturnal peak between 20:00 and 22:00 h with a low value in afternoon hours (15:00 h) with a mean BC mass concentration of 3.76±0.23 μg m −3. A scatter plot between BC mass concentration ( M b ) and total surface mass concentration ( M t ) showed significant positive correlation of 0.73 and was used to estimate mean mass fraction ( F BC ) for the study period, which was found to be 8.1±0.5%.

Weekly periodicities of aerosol properties observed at an urban location in India

Multi-year (~ 7 years) observations of aerosol optical and microphysical properties were conducted at a tropical urban location in Bangalore, India. As a consequence of rapid urbanization, Bangalore presents high local atmospheric emissions, which makes it an interesting site to study the effect of anthropogenic activities on aerosol properties. It has been found that both column (aerosol optical depth, AOD) and ground-level measurements (black carbon (BC) and composite aerosol mass) exhibit a weekly cycle with low aerosol concentrations on weekends. In comparison to the weekdays, the weekend reductions of aerosol optical depth, black carbon and composite aerosol mass concentrations were ~ 15%, 25% and 24%, respectively. The magnitude of weekend reduction of black carbon is as much as ~ 1 μg m − 3 . The similarity in the weekly cycle between the column and surface measurements suggests that the aerosol column loading at this location is governed by local anthropogenic emissions. The strongest weekly cycle in composite aerosol mass concentration was observed in the super micron mass range (> 1 μm). The weekly cycle of composite aerosol mass in the sub micron mass range (< 1 μm) was weak in comparison to the super micron aerosol mass.