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Atmospheric pollutants including ozone (O 3 ), sulfur dioxide (SO 2 ), oxides of nitrogen (NOx), carbon monoxide (CO), and inhalable particulate matter (PM 10 ) were measured in the central Indo-Gangetic Basin (IGB) at Patna, India, from 1st March 2013 to 31st December 2014, and significant variability was observed in the temporal patterns of these pollutant concentrations. The mean O 3 , SO 2 , NO, NO 2 , CO (trace gases: TG), and PM 10 (PM) concentrations were 14.5 ± 4.8, 5.9 ± 4.8, 23.1 ± 22, 20.6 ± 14.6 ppb, 1.5 ± 0.7 ppm, and 192.0 ± 132.8 μg/m 3 , respectively, over the study period. The highest concentrations of these species were during the post-monsoon and winter seasons except O 3 and SO 2 that showed the highest concentrations during the pre-monsoon. The lowest concentrations of TG and PM were observed during the monsoon season as a result of scavenging by rain. NO and NO 2 along with PM concentrations decreased by ~ 76, 19, and 63% when the wind speed (WS) was > 0.5 m/s. However, for O 3 , an opposite trend was observed with ~ 14% higher concentrations. The WS was negatively correlated with PM during the winter (− 0.48) and post-monsoon (− 0.32) seasons. In order to investigate the source region of TG and PM, 5-day air mass back trajectories were computed. The dominance of the air masses (92, 53, and 49%) were from the IGB is highly polluted during the winter, pre-monsoon, and post-monsoon, respectively. The TG and PM were observed much higher during these periods. During the biomass burning period (post-monsoon), the trajectory analysis showed that the TG and PM concentrations were around three-fold higher (flow from the IGB ) than the other seasons. To improve air quality over IGB, the mitigation measures should be designed to reduce emissions from both local and regional sources. [ABSTRACT FROM AUTHOR]

We use a recently developed parametrization to estimate the regional particle field in the summer time troposphere over Scandinavia that would result if the forest were the only source of particles. The calculated field is compared with available observational data. It is concluded that the needle leaf forest above 58°N alone is capable of producing aerosol mass concentrations corresponding to 12–50% of today's values in the boundary layer over Scandinavia. We also demonstrate that the forest itself could produce up to 200 CCN per cubic centimetre on average over Scandinavia and further show that an increase in temperature by 5.8 °C compared to today's average temperature could increase this CCN population by 40%. The study shows that we are able to approximate the natural aerosol field resulting from biogenic emissions over the boreal forest in the northern hemispheric region. This information provide an important contribution in the evaluation of the climate effect caused by anthropogenic emissions of particles over the forest and also opens the possibility to better address the climate feedbacks believed to be associated with the boreal region. [ABSTRACT FROM AUTHOR]

Using a pseudo-Lagrangian approach, changes in aerosol size distribution was investigated during southerly transport under clear sky conditions from Finnish Lapland to Hyytiälä. Seventy-nine individual transport cases were considered. The mean transport distance was 700 km and mean transport time 66 h. On average, a sevenfold increase in Aitken mode number concentration could be observed. An increase in number concentration was observed in virtually all the cases. Several of the studied cases were associated with indications of nucleation at the receptor site. Six of the cases were simulated in detail utilizing a box-model approach. Aerosol dynamics was evaluated using the University of Helsinki Multi-component Aerosol model. Particle formation was assumed to be controlled by a kinetic nucleation mechanism. Growth of particles was suggested to be controlled by, except water and ammonia, sulphuric acid, and some unknown species with saturation vapour pressure of 3 × 106 cm−3. This product was supposed to derive from terpene oxidation by hydroxyl radical, ozone, and nitrate radical. The investigation strongly suggests nucleation events occurring over large scales to be responsible for the observed number increase during transport under modelled conditions. Using a simplified two layer structure of the lowermost troposphere, we highlight the role of vertical exchange. Modelled growth rates were found to be in agreement with observational data, in the order of 1–2 nm h–1. In order to reproduce the observed growth rates, a molar yield of condensable products from terpene oxidation of 10% was required. Concentration of sulphuric acid and condensable organic vapours were on average 3 × 106 and 1.5 × 107 cm−3, respectively. [ABSTRACT FROM AUTHOR]

Aerosols play a key role in the radiation balance of the atmosphere. Here, we present evidence that the European boreal region is a substantial source of both aerosol mass and aerosol number. The investigation supplies a straightforward relation between emissions of monoterpenes and gas-to-particle formation over regions substantially lacking in anthropogenic aerosol sources. Our results show that the forest provides an aerosol population of 1000 to 2000 particles of climatically active sizes per cubic centimeter during the late spring to early fall period. This has important implications for radiation budget estimates and relevancy for the evaluation of feedback loops believed to determine our future climate. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is an important atmospheric aerosol constituent that affects the climate by absorbing (directly) the sunlight and modifying cloud characteristics (indirectly). Here, we present first time yearlong measurements of BC and carbon monoxide (CO) from an urban location of Guwahati located in the Brahmaputra River valley (BRV) in the northeast region of India from 1st July 2013 to 30th June 2014. Daily BC concentrations varied within the range of 2.86 to 11.56 μg m − 3 with an annual average of 7.17 ± 1.89 μg m − 3 , while, CO varied from 0.19 to 1.20 ppm with a mean value of 0.51 ± 0.19 ppm during the study period. The concentrations of BC (8.37 μg m − 3 ) and CO (0.67 ppm) were ~ 39% and ~ 55% higher during the dry months (October to March) than the wet months (April to September) suggesting that seasonal changes in meteorology and emission sources play an important role in controlling these species. The seasonal ΔBC/ΔCO ratios were highest (lowest) in the pre-monsoon (winter) 18.1 ± 1.4 μg m − 3 ppmv − 1 (12.6 ± 2.2 μg m − 3 ppmv − 1 ) which indicate the combustion of biofuel/biomass as well as direct emissions from fossil fuel during the pre-monsoon season. The annual BC emission was estimated to be 2.72 Gg in and around Guwahati which is about 44% lower than the mega city ‘Delhi’ (4.86 Gg). During the study period, the annual mean radiative forcing (RF) at the top of the atmosphere (TOA) for clear skies of BC was + 9.5 Wm − 2 , however, the RF value at the surface (SFC) was − 21.1 Wm − 2 which indicates the net warming and cooling effects, respectively. The highest RF at SFC was in the month of April (− 30 Wm − 2 ) which is coincident with the highest BC mass level. The BC atmospheric radiative forcing (ARF) was + 30.16 (annual mean) Wm − 2 varying from + 23.1 to + 43.8 Wm − 2 . The annual mean atmospheric heating rate (AHR) due to the BC aerosols was 0.86 K day − 1 indicates the enhancement in radiation effect over the study region. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) captured the seasonal cycle of observed BC fairly well but underestimated the observed BC during the month of May–August. Model results show that BC at Guwahati is controlled mainly by anthropogenic emissions except during the pre-monsoon season when open biomass burning also makes a similar contribution. [ABSTRACT FROM AUTHOR]

The ground and vertical profiles of particulate matter (PM) were mapped as part of a pilot study using a Tethered balloon within the lower troposphere (1000 m) during the foggy episodes in the winter season of 2015–16 in New Delhi, India. Measurements of black carbon (BC) aerosol and PM < 2.5 and 10 μm (PM 2.5 & PM 10 respectively) concentrations and their associated particulate optical properties along with meteorological parameters were made. The mean concentrations of PM 2.5 , PM 10 , BC 370 nm, and BC 880 nm were observed to be 146.8 ± 42.1, 245.4 ± 65.4, 30.3 ± 12.2, and 24.1 ± 10.3 μg m − 3 , respectively. The mean value of PM 2.5 was ~ 12 times higher than the annual US-EPA air quality standard. The fraction of BC in PM 2.5 that contributed to absorption in the shorter visible wavelengths (BC 370 nm ) was ~ 21%. Compared to clear days, the ground level mass concentrations of PM 2.5 and BC 370 nm particles were substantially increased (59% and 24%, respectively) during the foggy episode. The aerosol light extinction coefficient (σ ext ) value was much higher (mean: 610 Mm − 1 ) during the lower visibility (foggy) condition. Higher concentrations of PM 2.5 (89 μg m − 3 ) and longer visible wavelength absorbing BC 880 nm (25.7 μg m − 3 ) particles were observed up to 200 m. The BC 880 nm and PM 2.5 aerosol concentrations near boundary layer (1 km) were significantly higher (~ 1.9 and 12 μg m − 3 ), respectively. The BC (i.e BC tot ) aerosol direct radiative forcing (DRF) values were estimated at the top of the atmosphere (TOA), surface (SFC), and atmosphere (ATM) and its resultant forcing were - 75.5 Wm − 2 at SFC indicating the cooling effect at the surface. A positive value (20.9 Wm − 2 ) of BC aerosol DRF at TOA indicated the warming effect at the top of the atmosphere over the study region. The net DRF value due to BC aerosol was positive (96.4 Wm − 2 ) indicating a net warming effect in the atmosphere. The contribution of fossil and biomass fuels to the observed BC aerosol DRF values was ~ 78% and ~ 22%, respectively. The higher mean atmospheric heating rate (2.71 K day − 1 ) by BC aerosol in the winter season would probably strengthen the temperature inversion leading to poor dispersion and affecting the formation of clouds. Serious detrimental impacts on regional climate due to the high concentrations of BC and PM (especially PM 2.5 ) aerosol are likely based on this study and suggest the need for immediate, stringent measures to improve the regional air quality in the northern India. [ABSTRACT FROM AUTHOR]

Samples of rainwater (RW) were collected to characterize the chemistry and sources in two representative megacities at Pune (Southwest) and Delhi (Northern) India from 2011 to 2014 across two seasons: monsoon (MN) and non-monsoon (NMN). Collected RW samples were analyzed for major chemical constituents (F − , Cl − , SO 4 2− , NO 3 − , NH 4 + , Na + , K + , Ca 2+ , and Mg 2+ ), pH and conductivity. In addition, bicarbonate (HCO 3 − ) was also estimated. The mean pH values of the RW were >6 at Pune and <6 at Delhi and 4% and 26% were acidic, respectively. The mean sum of all measured ionic species in Pune and Delhi was 304.7 and 536.4 μeq/l, respectively, indicating that significant atmospheric pollution effects in these Indian mega cities. Both the Ca 2+ and SO 4 2− were the dominant ions, accounting for 43% (Pune) and 54% (Delhi) of the total ions. The sum of measured ions during the NMN period was greater than the NM period by a factor of 1.5 for Pune (278.4: NM and 412.1: NMN μeq/l) and a factor of about 2.5 for Delhi (406 and 1037.7 μeq/l). The contributions of SO 4 2− and NO 3 − to the RW acidity were ∼40% and 60%, respectively, at Pune and correspondingly, 36% and 64% at Delhi. The concentrations of secondary aerosols (SO 4 2− and NO 3 − ) were higher by a factor of two and three when the air masses were transported to Pune from the continental side. At Delhi, the concentrations of SO 4 2− , NO 3 − , Ca 2+ , and Mg 2+ were significantly higher when the air masses arrive from Punjab, Haryana, and Pakistan indicating the greater atmospheric pollution over the Indo-Gangetic Plain. Positive matrix factorization was applied to the source apportionment of the deposition fluxes of these ions. Three factors were obtained for Pune and four for Delhi. The sources at Pune were secondary aerosols from fossil fuel combustion, soil dust, and marine, whereas, at Delhi, the sources were soil, fossil fuel combustion, biomass burning, and industrial chlorine. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols are one of the most uncertain drivers of global climate change. The prevailing view is that BC mass concentrations are low in rural areas where industrialization and vehicular emissions are at a minimum. As part of a national research program called the “Ganga Basin Ground Based Experiment-2014 under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase-III” of Ministry of Earth Sciences, Government of India, the continuous measurements of BC and particulate matter (PM) mass concentrations, were conducted in a rural environment in the highly-polluted Indo-Gangetic Plain region during 16th June to 15th August (monsoon period), 2014. The mean mass concentration of BC was 4.03 (± 0.85) μg m − 3 with a daily variability between 2.4 and 5.64 μg m − 3 , however, the mean mass PM concentrations [near ultrafine (PM 1.0 ), fine (PM 2.5 ) and inhalable (PM 10 )] were 29.1(± 16.2), 34.7 (± 19.9) and 43.7 (± 28.3) μg m − 3 , respectively. The contribution of BC in PM 1.0 was approximately 13%, which is one of the highest being recorded. Diurnally, the BC mass concentrations were highest (mean: 5.89 μg m − 3 ) between 20:00 to 22:00 local time (LT) due to the burning of biofuels/biomass such as wood, dung, straw and crop residue mixed with dung by the local residents for cooking purposes. The atmospheric direct radiative forcing values due to the composite and BC aerosols were determined to be + 78.3, + 44.9, and + 45.0 W m − 2 and + 42.2, + 35.4 and + 34.3 W m − 2 during the months of June, July and August, respectively. The corresponding atmospheric heating rates (AHR) for composite and BC aerosols were 2.21, 1.26 and 1.26; and 1.19, 0.99 and 0.96 K day − 1 for the month of June, July and August, respectively, with a mean of 1.57 and 1.05 K day − 1 which was 33% lower AHR (BC) than for the composite particles during the study period. This high AHR underscores the importance of absorbing aerosols such as BC contributed by residential cooking using biofuels in India. Our study demonstrates the need for immediate, effective regulations and policies that mitigate the emission of BC particles from domestic cooking in rural areas of India. [ABSTRACT FROM AUTHOR]

The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the size-resolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth. [ABSTRACT FROM AUTHOR]

In this study, we look for anthropogenic aerosol effects in southern Scandinavia's clouds under the influence of moderate levels of pollution and relatively weak dynamic forcing. This was done by comparing surface aerosol measurements with convective cloud microphysical profiles produced from satellite image analyses. The results show that the clouds associated with the anthropogenic-affected air with high PM0.5, had to acquire a vertical development of ∼3.5 km before forming precipitation-sized particles, compared to less than 1 km for the clouds associated with low PM0.5 air-masses. Additionally, a comparison of profiles with precipitation was done with regard to different potentially important parameters. For precipitating clouds the variability of the cloud thickness needed to produce the precipitation (Δ h14) is directly related to PM0.5 concentrations, even without considering atmospheric stability, the specific aerosol size distribution or the aerosols' chemical composition. Each additional 1 μg m−3 of PM0.5 was found to increase Δ h14 by ∼200–250 m. Our conclusion is that it is indeed possible to detect the effects of anthropogenic aerosol on the convective clouds in southern Scandinavia despite modest aerosol masses. It also emphasizes the importance of including aerosol processes in climate-radiation models and in numerical weather prediction models. [ABSTRACT FROM AUTHOR]

One year of aerosol size distribution and chemical composition measurements conducted at the Zeppelin station on Svalbard (78° 58′ N and 11° 53′E) is presented. The data, which cover the period March 2000–April 2001, show a very strong seasonal dependence of the number mode particle size. The transition from one seasonal characteristic regime to the other occurs rapidly and takes place over only a few days. As expected, the largest integrated aerosol surface and particle volumes are observed during the Arctic haze period in spring. On a seasonal scale the total number density covariate with the incoming solar radiation, which points to photochemistry as an important component during new particle formation in the Arctic summer. However, maximum number densities are observed during the second part of the summer concurrent with a relative reduction in the incoming radiation. The onset of this period of enhanced particle number densities coincides in time with the surface temperature remaining steadily above the freezing point and the melting of the snow cover. A similar transition occurring over the Siberian tundra is proposed as a potential source of aerosol precursor gases, which could explain the enhanced particle number densities during the second half of the summer. A second maximum of ammonium in particles during late summer and fall, concurrent with a reduction in sea salt and nss-sulfate present in particles would be consistent with continental source without a significant anthropogenic component. The data presented in the study also illustrate the usefulness of measurements that extend over several seasons where phenomenon that occur with in one season, the summer in this case, can be put into context. [Copyright &y& Elsevier]

To determine the direct and indirect effects of aerosols on climate, it is important to know the spatial and temporal variations in cloud condensation nuclei (CCN) concentrations. Although many types of CCN measurements are available, extensive CCN measurements are challenging because of the complexity and high operating cost, especially in remote areas. As aerosol optical depth (AOD) can be readily observed by remote sensing, many attempts have been made to estimate CCN concentrations from AOD. In this study, the CCN–AOD relationship is parameterized based on CCN ground measurements from the Zeppelin Observatory (78.91° N, 11.89° E, 474 m asl) in the Arctic region. The AOD measurements were obtained from the Ny-Ålesund site (78.923° N, 11.928° E) and Modern-Era Retrospective Analysis for Research and Applications, Version 2 reanalysis. Our results show a CCN–AOD correlation with a coefficient of determination R2 of 0.59. Three additional estimation models for CCN were presented based on the following data: (i) in situ aerosol chemical composition, (ii) in situ aerosol optical properties, and (iii) chemical composition of AOD obtained from reanalysis data. The results from the model using in situ aerosol optical properties reproduced the observed CCN concentration most efficiently, suggesting that the contribution of BC to CCN concentration should be considered along with that of sulfate. ● Relationship between CCN concentration and AOD was parameterized with statistically significant. ● AOD from MERRA-2 and MODIS were comparable with ground-based measurements of AOD. ● In-situ aerosol optical properties reproduce the CCN most efficiently. [ABSTRACT FROM AUTHOR]