Chemical Constituents of Carbonaceous and Nitrogen Aerosols over Thumba Region, Trivandrum, India

Aerosol filter samples collected at a tropical coastal site Thumba over Indian region were analysed for water-soluble ions, total carbon and nitrogen, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon/nitrogen and their sources for different seasons of the year. For the entire study period, the order of abundance of ions showed the dominance of secondary ions, such as SO₄^2-, NO₃^-, and NH₄⁺. On average, Mg²⁺ (56%), K⁺ (11%), SO₄^2- (8.8%), and Ca²⁺ (8.1%) contributions were from maritime influence. There was significant chloride depletion due to enhanced levels of inorganic acids, such as SO₄^2- and NO₃^-. Total carbon contributed 21% of the aerosol total suspended particulate matter in which 85% is organic carbon. Primary combustion-generated carbonaceous aerosols contributed 41% of aerosol mass for the entire study period. High average ratios of OC/EC (5.5 ± 1.8) and WSOC/OC (0.38 ± 0.11) suggest that organic aerosols are predominantly comprised of secondary species. In our samples, major fraction (89 ± 9%) was found to be inorganic nitrate in total nitrogen (TN). Good correlations (R ² ≥ 0.82) were observed between TN with NO₃^- plus NH₄⁺, indicating that nitrate and ammonium ions account for a significant portion of TN. The temporal variations in the specific carbonaceous aerosols and air mass trajectories demonstrated that several pollutants and/or their precursor compounds are likely transported from north western India and the oceanic regions.

Secondary Organic Aerosol Formation over Coastal Ocean: Inferences from Atmospheric Water-Soluble Low Molecular Weight Organic Compounds

A lack of consensus on the distributions and formation pathways of secondary organic aerosols (SOA) over oceanic regions downwind of pollution sources limits our ability to assess their climate impact globally. As a case study, we report here on water-soluble SOA components such as dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls in the continental outflows from the Indo-Gangetic Plain (IGP) and Southeast Asia (SEA) to the Bay of Bengal. Oxalic acid (C₂) is the dominant species followed by succinic (C₄) and glyoxylic acids (ωC₂) in the outflow. Nonsea-salt SO₄^2- also dominates (∼70%) total water-soluble inorganic constituents and correlates well with aerosol liquid water content (LWC) and C₂, indicating their production through aqueous phase photochemical reactions. Furthermore, mass ratios of dicarboxylic acids (C₂/C₄, C₂/ωC₂), and their relative abundances in water-soluble organic carbon and total organic carbon are quite similar between the two continental (IGP and SEA) outflows, indicating the formation of SOA through aqueous phase photochemical reactions in LWC-enriched aerosols, largely controlled by anthropogenic SO₄^2-.

Assessment of the clear-sky bias issue using continuous PM10 data from two AERONET sites in Korea

A bias in clear-sky conditions that will be involved in estimating particulate matter (PM) concentration from aerosol optical depth (AOD) was examined using PM₁₀ from two Aerosol Robotic Network sites in Korea. The study periods were between 2004 and 2007 at Anmyon and between 2003 and 2011 at Gosan, when both PM₁₀ and AOD were available. Mean PM₁₀ when AOD was available (PM_AOD) was higher than that from all PM₁₀ data (PM_all) by 5.1 and 9.9μg/m³ at Anmyon and Gosan, which accounted for 11% and 26% of PM_all, respectively. Because of a difference between mean PM₁₀ under daytime clear-sky conditions (PM_clear) and PM_AOD, the variations in ΔPM₁₀, the difference of PM_all from PM_clear rather than from PM_AOD, were investigated. Although monthly variations in ΔPM₁₀ at the two sites were different, they were positively correlated to those in ΔT, similarly defined as ΔPM₁₀ except for temperature, at both sites. ΔPM₁₀ at Anmyon decreased to a negative value in January due to an influence of the Siberian continental high-pressure system while ΔPM₁₀ at Gosan was high in winter due to an effect of photochemical production at higher temperatures than at Anmyon.

Atmospheric aerosol radiative forcing over a semi-continental location Tripura in North-East India: Model results and ground observations

Northeast India (NEI) is located within the boundary of the great Himalayas in the north and the Bay of Bengal (BoB) in the southwest, experiences the mixed influence of the westerly dust advection from the Indian desert, anthropogenic aerosols from the highly polluted Indo-Gangetic Plains (IGP) and marine aerosols from BoB. The present study deals with the estimation and characterization of aerosol radiative forcing over a semi-continental site Tripura, which is a strategic location in the western part of NEI having close proximity to the outflow of the IGP. Continuous long term measurements of aerosol black carbon (BC) mass concentrations and columnar aerosol optical depth (AOD) are used for the estimation of aerosol radiative forcing in each monthly time scale. The study revealed that the surface forcing due to aerosols was higher during both winter and pre-monsoon seasons, having comparable values of 32W/m² and 33.45W/m² respectively. The atmospheric forcing was also higher during these months due to increased columnar aerosol loadings (higher AOD ~0.71) shared by abundant BC concentrations (SSA ~0.7); while atmospheric forcing decreased in monsoon due to reduced magnitude of BC (SSA ~0.94 in July) as well as columnar AOD. The top of the atmosphere (TOA) forcing is positive in pre-monsoon and monsoon months with the highest positive value of 3.78W/m² in June 2012. The results are discussed in light of seasonal source impact and transport pathways from adjacent regions.

Formation, features and controlling strategies of severe haze-fog pollutions in China

With rapid industrialization and urbanization, China is facing a great challenge with regard to severe fog-haze pollutions, which were characterized by high fine particulate concentration level and visibility impairment. The control strategies for atmosphere pollutions in China were not only cutting-edge topics of atmospheric research, but also an urgent issue to be addressed by the Chinese government and the public. Focused on the core scientific issues of the haze and fog pollution, this paper reviews the main studies conducted in China, especially after 2010, including formation mechanisms, evolution features, and factors contributing to the fog-haze pollutions. Present policy and control strategies were synoptically discussed. The major challenges ahead will be stated and recommendations for future research directions are proposed at the end of this Review.

Vertical distribution of ambient aerosol extinctive properties during haze and haze-free periods based on the Micro-Pulse Lidar observation in Shanghai

Ambient aerosols make a significant contribution to the environment and climate through their optical properties. In this study, the aerosol extinction coefficient and Aerosol optical depth (AOD) retrieved using the Fernald Method from the ground-based Micro-Pulse Lidar (MPL) were used to investigate the characteristics of aerosols during haze and haze-free periods in Shanghai. There were 216 haze days including 145 dry haze days, 39 damp haze days and 32days of both dry and damp haze in Shanghai from March 2009 to February 2010. During the haze periods, aerosols were concentrated mainly below 600m resulting in the most severe pollution layer in Shanghai. In contrast to the aerosol optical properties during haze-free periods, aerosol extinction coefficients and AOD were larger in the lower altitude (below 1km) during haze periods. The lowest 1km contributed 53-72% of the Aerosol optical depth (AOD) below 6km for the haze periods and <41% of that for the haze-free periods except summer. According to the analysis of influencing factors, although atmospheric convection was strong in summer which led to reduce the extinction, the highest occurrence of haze with relatively low aerosol extinction most of time was in summer, which resulted from the factors such as higher relative humidity, temperature and more solar radiation causing hygroscopic growth of particles and formation of secondary aerosols; in spring and autumn, there was less haze occurrences because the boundary layer was relatively higher, which allowed pollutants to diffuse more easily, but spring was the second most frequency season of haze due to frequent dust transport from the north; in winter high concentrations of particles and low boundary layer height were not beneficial to the diffusion of pollutants near the surface and caused haze occurrence rather high with high aerosol extinction.

Black carbon solar absorption suppresses turbulence in the atmospheric boundary layer

The introduction of cloud condensation nuclei and radiative heating by sunlight-absorbing aerosols can modify the thickness and coverage of low clouds, yielding significant radiative forcing of climate. The magnitude and sign of changes in cloud coverage and depth in response to changing aerosols are impacted by turbulent dynamics of the cloudy atmosphere, but integrated measurements of aerosol solar absorption and turbulent fluxes have not been reported thus far. Here we report such integrated measurements made from unmanned aerial vehicles (UAVs) during the CARDEX (Cloud Aerosol Radiative Forcing and Dynamics Experiment) investigation conducted over the northern Indian Ocean. The UAV and surface data reveal a reduction in turbulent kinetic energy in the surface mixed layer at the base of the atmosphere concurrent with an increase in absorbing black carbon aerosols. Polluted conditions coincide with a warmer and shallower surface mixed layer because of aerosol radiative heating and reduced turbulence. The polluted surface mixed layer was also observed to be more humid with higher relative humidity. Greater humidity enhances cloud development, as evidenced by polluted clouds that penetrate higher above the top of the surface mixed layer. Reduced entrainment of dry air into the surface layer from above the inversion capping the surface mixed layer, due to weaker turbulence, may contribute to higher relative humidity in the surface layer during polluted conditions. Measurements of turbulence are important for studies of aerosol effects on clouds. Moreover, reduced turbulence can exacerbate both the human health impacts of high concentrations of fine particles and conditions favorable for low-visibility fog events.

An Overview of Small Unmanned Aerial Vehicles for Air Quality Measurements: Present Applications and Future Prospectives

Assessment of air quality has been traditionally conducted by ground based monitoring, and more recently by manned aircrafts and satellites. However, performing fast, comprehensive data collection near pollution sources is not always feasible due to the complexity of sites, moving sources or physical barriers. Small Unmanned Aerial Vehicles (UAVs) equipped with different sensors have been introduced for in-situ air quality monitoring, as they can offer new approaches and research opportunities in air pollution and emission monitoring, as well as for studying atmospheric trends, such as climate change, while ensuring urban and industrial air safety. The aims of this review were to: (1) compile information on the use of UAVs for air quality studies; and (2) assess their benefits and range of applications. An extensive literature review was conducted using three bibliographic databases (Scopus, Web of Knowledge, Google Scholar) and a total of 60 papers was found. This relatively small number of papers implies that the field is still in its early stages of development. We concluded that, while the potential of UAVs for air quality research has been established, several challenges still need to be addressed, including: the flight endurance, payload capacity, sensor dimensions/accuracy, and sensitivity. However, the challenges are not simply technological, in fact, policy and regulations, which differ between countries, represent the greatest challenge to facilitating the wider use of UAVs in atmospheric research.

Optical and thermal characteristics of carbonaceous aerosols measured at an urban site in Gwangju, Korea, in the winter of 2011

Carbonaceous components (organic carbon [OC] and elemental carbon [EC]) and optical properties (light absorption and scattering) of fine particulate matter (aerodynamic diameter <2.5 μm; PM2.5) were simultaneously measured at an urban site in Gwangju, Korea, during the winter of 2011. OC was further classified into OC1, OC2, OC3, and OC4, based on a temperature protocol using a Sunset OC/EC analyzer. The average OC and EC concentrations were 5.0 ± 2.5 and 1.7 ± 0.9 μg C m(-3), respectively. The average single-scattering albedo (SSA) at a wavelength of 550 nm was 0.58 ± 0.11, suggesting that the aerosols observed in the winter of 2011 had a local warming effect in this area. During the whole sampling period, "stagnant PM" and "long-range transport PM" events were identified. The light absorption coefficient (babs) was higher during the stagnant PM event than during the long-range transport PM event due to the existence of abundant light-absorbing OC during the stagnant PM event. In particular, the OC2 and OC3 concentrations were higher during the stagnant PM event than those during the long-range transport event, suggesting that OC2 and OC3 might be more related to the light-absorbing OC. The light scattering coefficient (bscat) was similar between the events. On average, the mass absorption efficiency attributed to EC (σEC) was 9.6 m(2) g(-1), whereas the efficiency attributed to OC (σOC) was 1.8 m(2) g(-1) at λ = 550 nm. Furthermore, the σEC is comparable among the PM event days, but the σOC for the stagnant PM event was significantly higher than that for the long-range transport PM event (1.7 vs. 0.5).

IMPLICATIONS

Optical and thermal properties of carbonaceous aerosol were measured at Gwangju, and carbonaceous aerosol concentration and optical property varied between "stagnant PM" and "long-range transport PM" events. More abundant light absorbing OC was observed during the stagnant PM event.

Vertically-resolved profiles of mass concentrations and particle backscatter coefficients of Asian dust plumes derived from lidar observations of silicon dioxide

This study presents a method to retrieve vertically-resolved profiles of dust mass concentrations by analyzing Raman lidar signals of silicon dioxide (quartz) at 546nm. The observed particle plumes consisted of mixtures of East Asian dust with anthropogenic pollution. Our method for the first time allows for extracting the contribution of the aerosol component "pure dust" contained in the aerosol type "polluted dust". We also propose a method that uses OPAC (Optical Properties of Aerosols and Clouds) and the mass concentrations profiles of dust in order to derive profiles of backscatter coefficients of pure dust in mixed dust/pollution plumes. The mass concentration of silicon dioxide (quartz) in the atmosphere can be estimated from the backscatter coefficient of quartz. The mass concentration of dust is estimated by the weight percentage (38-77%) of mineral quartz in Asian dust. The retrieved dust mass concentrations are classified into water soluble, nucleation, accumulation, mineral-transported and coarse mode according to OPAC. The mass mixing ratio of 0.018, 0.033, 0.747, 0.130 and 0.072, respectively, is used. Dust extinction coefficients at 550nm were calculated by using OPAC and prescribed number concentrations for each of the 5 components. Dust backscatter coefficients were calculated from the dust extinction coefficients on the basis of a lidar ratio of 45±3sr at 532nm. We present results of quartz-Raman measurements carried out on the campus of the Gwangju Institute of Science and Technology (35.10°N, 126.53°E) on 15, 16, and 21 March 2010.

An integrated campaign for investigation of winter-time continental haze over Indo-Gangetic Basin and its radiative effects

An outflow of continental haze occurs from Indo-Gangetic Basin (IGB) in the North to Bay of Bengal (BoB) in the South. An integrated campaign was organized to investigate this continental haze during December 2013-February 2014 at source and remote regions within IGB to quantify its radiative effects. Measurements were carried out at three locations in eastern India; 1) Kalas Island, Sundarban (21.68°N, 88.57°E) - an isolated island along the north-east coast of BoB, 2) Kolkata (22.57°N, 88.42°E) - an urban metropolis and 3) Siliguri (26.70°N, 88.35°E) - an urban region at the foothills of eastern Himalayas. Ground-based AOD (at 0.5 μm) is observed to be maximum (1.25±0.18) over Kolkata followed by Siliguri (0.60±0.17) and minimum over Sundarban (0.53±0.18). Black carbon concentration is found to be maximum at Kolkata (21.6±6.6 μg·m(-3)) with almost equal concentrations at Siliguri (12.6±5.2 μg·m(-3)) and Sundarban (12.3±3.0 μg·m(-3)). Combination of MODIS-AOD and back-trajectories analysis shows an outflow of winter-time continental haze originating from central IGB and venting out through Sundarban towards BoB. This continental haze with high extinction coefficient is identified up to central BoB using CALIPSO observations and is found to contribute ~75% to marine AOD over central BoB. This haze produces significantly high aerosol radiative forcing within the atmosphere over Kolkata (75.4 Wm(-2)) as well as over Siliguri and Sundarban (40 Wm(-2)) indicating large forcing over entire IGB, from foothills of the Himalayas to coastal region. This winter-time continental haze also causes about similar radiative heating (1.5 K·day(-1)) from Siliguri to Sundarban which is enhanced over Kolkata (3 K·day(-1)) due to large emission of local urban aerosols. This high aerosol heating over entire IGB and coastal region of BoB can have considerable impact on the monsoonal circulation and more importantly, such haze transported over to BoB can significantly affect the marine hydrological cycle.

Winter time chemical characteristics of aerosols over the Bay of Bengal: continental influence

As part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) conducted under the Geosphere Biosphere Programme of Indian Space Research Organisation, ship-based aerosol sampling was carried out over the marine environment of Bay of Bengal (BoB) during the northern winter months of December 2008 to January 2009. About 101 aerosol samples were collected, covering the region from 3.4° to 21° N latitude and 76° to 98° E longitude-the largest area covered-including the south east (SE) BoB for the first time. These samples were subjected to gravimetric and chemical analysis and the total aerosol loading as well the mass concentration of the ionic species namely F(-), Cl(-), Br(-), NO2 (-), NO3 (-), PO4 (2-), SO4 (2-), NH4 (+), etc. and the metallic species, Na, Mg, Ca, K, Al, Fe, Mn, Zn, and Pb were estimated for each sample. Based on the spatial distribution of individual chemical species, the air flow pattern, and airmass back trajectory analysis, the source characteristics of aerosols for different regions of BoB were identified. Significant level of continental pollution was noticed over BoB during winter. While transport of pollution from Indo-Gangetic Plain (IGP) contributed to aerosols over north BoB, those over SE BoB were influenced by SE Asia. A quantitative study on the wind-induced production of sea salt aerosols and a case study on the species dependent effect of rainfall are also presented in this paper.

Columnar-integrated aerosol optical properties and classification of different aerosol types over the semi-arid region, Anantapur, Andhra Pradesh

This study presents a characterization of aerosol columnar properties measured at a semi-arid station Anantapur in the southern part of India during the period from October 2012 to September 2013. Aerosol optical depth (AOD) and Angstrom exponent (α) have been retrieved from Microtops II Sunphotometer over the observation site. The results show that a pronounced spectral and monthly variability in the optical properties of aerosols is mainly due to anthropogenic sources. The results show that the spectral curvature can effectively be used as a tool for aerosol type discrimination, since the fine-mode aerosols exhibit negative curvature, while the coarse-mode particles are positive. The classification of aerosols is also proposed by using the values of AOD at 500 nm and Angstrom exponent values (α(380-870)) by applying threshold values obtained from the frequency distribution of AOD. The results of the analysis were identified by four individual components (anthropogenic/biomass burning, coarse/dust, coarse/marine, clean continental) of different origin and compositions. The most frequent situations observed over the site are that due to the anthropogenic/biomass burning situations which account for about 45.37%, followed by coarse/dust (43.64%), clean continental (7.2%) and coarse/marine (3.82%) during summer. The identification of the aerosol source type and the modification processes are analyzed by using the Gobbi et al. (2007) classification scheme based on the measured scattering properties (α, dα) derived from the Microtops II Sunphotometer.

Effects of mixing states on the multiple-scattering properties of soot aerosols

The radiative properties of soot aerosols are highly sensitive to the mixing states of black carbon particles and other aerosol components. Light absorption properties are enhanced by the mixing state of soot aerosols. Quantification of the effects of mixing states on the scattering properties of soot aerosol are still not completely resolved, especially for multiple-scattering properties. This study focuses on the effects of the mixing state on the multiple scattering of soot aerosols using the vector radiative transfer model. Two types of soot aerosols with different mixing states such as external mixture soot aerosols and internal mixture soot aerosols are studied. Upward radiance/polarization and hemispheric flux are studied with variable soot aerosol loadings for clear and haze scenarios. Our study showed dramatic changes in upward radiance/polarization due to the effects of the mixing state on the multiple scattering of soot aerosols. The relative difference in upward radiance due to the different mixing states can reach 16%, whereas the relative difference of upward polarization can reach 200%. The effects of the mixing state on the multiple-scattering properties of soot aerosols increase with increasing soot aerosol loading. The effects of the soot aerosol mixing state on upwelling hemispheric flux are much smaller than in upward radiance/polarization, which increase with increasing solar zenith angle. The relative difference in upwelling hemispheric flux due to the different soot aerosol mixing states can reach 18% when the solar zenith angle is 75°. The findings should improve our understanding of the effects of mixing states on the optical properties of soot aerosols and their effects on climate. The mixing mechanism of soot aerosols is of critical importance in evaluating the climate effects of soot aerosols, which should be explicitly included in radiative forcing models and aerosol remote sensing.

Aerosol optical properties under the condition of heavy haze over an urban site of Beijing, China

In January 2013, several serious haze pollution events happened in North China. Cimel sunphotometer measurements at an urban site of Beijing (Chinese Academy of Meteorological Sciences-CAMS) from 1 to 30 January 2013 were used to investigate the detailed variation of aerosol optical properties. It was found that Angstrom exponents were mostly larger than 0.80 when aerosol optical depth values are higher than 0.60 at the urban region of Beijing during January 2013. The aerosol optical depth (AOD) at the urban region of Beijing can remain steady at approximately 0.40 before haze happening and then increased sharply to more than 1.50 at 500 nm with the onset of haze, which suggests that the fine-mode AOD is a factor of 20 of the coarse-mode AOD during a serious haze pollution event. The single scattering albedo was approximately 0.90 ± 0.03 at 440, 675, 870 and 1,020 nm during the haze pollution period. The single scattering albedo at 440 nm as a function of the fine-mode fraction was relatively consistent, but it was highly variable at 675, 870 and 1,020 nm. Except on January 12 and 18, all the fine-mode particle volumes were larger than those of coarse particles, which suggests that fine particles from anthropogenic activities made up most of the haze. Aerosol type classification analysis showed that the dominant aerosol types can be classified as both "mixed" and "urban/industrial (U/I) and biomass burning (BB)" categories during the heavy haze period of Beijing in January of 2013. The mixed category occurrence was about 31 %, while the U/I and BB was about 69 %.

Interactions between biomass-burning aerosols and clouds over Southeast Asia: current status, challenges, and perspectives

The interactions between aerosols, clouds, and precipitation remain among the largest sources of uncertainty in the Earth's energy budget. Biomass-burning aerosols are a key feature of the global aerosol system, with significant annually-repeating fires in several parts of the world, including Southeast Asia (SEA). SEA in particular provides a "natural laboratory" for these studies, as smoke travels from source regions downwind in which it is coupled to persistent stratocumulus decks. However, SEA has been under-exploited for these studies. This review summarizes previous related field campaigns in SEA, with a focus on the ongoing Seven South East Asian Studies (7-SEAS) and results from the most recent BASELInE deployment. Progress from remote sensing and modeling studies, along with the challenges faced for these studies, are also discussed. We suggest that improvements to our knowledge of these aerosol/cloud effects require the synergistic use of field measurements with remote sensing and modeling tools.

A review on black carbon emissions, worldwide and in China

Black carbon (BC) produced from open burning (OB) and controlled combustion (CC) is a range of carbonaceous products of incomplete combustion of biomass and fossil fuel, and is deemed as one of the major contributors to impact global environment and human health. BC has a strong relationship with POPs, in waste combustion, BC promotes the formation of POPs, and then the transport of POPs in the environment is highly influenced by BC. However less is known about BC formation, measurement and emissions estimation especially in developing countries such as China. Different forms of BC are produced both in CC and OB. BC emission characteristics and combustion parameters which determine BC emissions from CC and OB are discussed. Recent studies showed a lack of common methodology and the resulting data for describing the mechanisms related to BC formation during combustion processes. Because BC is a continuum carbonaceous combustion product, different sampling and measuring methods are used for measuring their emissions with great quantitative uncertainty. We discuss the commonly used BC sampling and measuring methods along with the causes for uncertainty and measures to minimizing the uncertainty. Then, we discuss the estimations of BC emission factors and emission inventory for CC and OB sources. The total emissions of BC from CC and OB in China are also estimated and compared with previous BC emission inventories in this review and we find the inventories tend to be overestimated. As China becomes the largest contributor to global BC emissions, studies for characterizing BC emissions from OB and CC sources are absent in China. Finally, we comment on the current state of BC emission research and identify major deficiencies that need to overcome. Moreover, the advancement in research tools, measuring technique in particular, as discussed in this review is critical for researchers in developing countries to improve their capability to study BC emissions for addressing the growing climate change and public health concerns.

Effects of morphology on the radiative properties of internally mixed light absorbing carbon aerosols with different aging status

Light absorbing carbon aerosols play a substantial role in climate change through radiative forcing, which is the dominant absorber of solar radiation. Radiative properties of light absorbing carbon aerosols are strongly dependent on the morphological factors and the mixing mechanism of black carbon with other aerosol components. This study focuses on the morphological effects on the optical properties of internally mixed light absorbing carbon aerosols using the numerically exact superposition T-matrix method. Three types aerosols with different aging status such as freshly emitted BC particles, thinly coated light absorbing carbon aerosols, heavily coated light absorbing carbon aerosols are studied. Our study showed that morphological factors change with the aging of internally mixed light absorbing carbon aerosols to result in a dramatic change in their optical properties. The absorption properties of light absorbing carbon aerosols can be enhanced approximately a factor of 2 at 0.67 um, and these enhancements depend on the morphological factors. A larger shell/core diameter ratio of volume-equivalent shell-core spheres (S/C), which indicates the degree of coating, leads to stronger absorption. The enhancement of absorption properties accompanies a greater enhancement of scattering properties, which is reflected in an increase in single scattering albedo (SSA). The enhancement of single scattering albedo due to the morphological effects can reach a factor of 3.75 at 0.67 μm. The asymmetry parameter has a similar yet smaller enhancement. Moreover, the corresponding optical properties of shell-and-core model determined by using Lorenz -Mie solutions are presented for comparison. We found that the optical properties of internally mixed light absorbing carbon aerosol can differ fundamentally from those calculated for the Mie theory shell-and-core model, particularly for thinly coated light absorbing carbon aerosols. Our studies indicate that the complex morphology of internally mixed light absorbing carbon aerosols must be explicitly considered in climate radiation balance.

Characteristics and formation mechanism of a heavy air pollution episode caused by biomass burning in Chengdu, Southwest China

To track the chemical characteristics and formation mechanism of biomass burning pollution, the hourly variations of meteorological factors and pollutant concentrations during a heavy pollution on 18-21 May, 2012 in Chengdu are presented in this study. The episode was the heaviest and most long-lasting pollution event in the historical record of Chengdu caused by a combination of stagnant dispersion conditions and enhanced PM2.5 emission from intensive biomass burning, with peak values surpassing 500 μg m(-3). The event was characterized by three nighttime peaks, relating to the burning practice and decreased boundary layer height at night. The prevailing northeasterly wind during nighttime preferentially brought more pollutants to the urban regions from northern suburbs of Chengdu, where dense fire spots were observed. Due to the obstruction of hilly topography and weak wind speed, minor regional features were reflected from the PM10 variations in nearby cities, whereas the long-distance transport of the plume impacted extensive regions in northern and eastern China. Carbon monoxide (CO) concentrations increased by more than 200%, while exceptionally high PM2.5 levels of 190.1 and 268.4 μg m(-3) on 17 May and 18 May, were observed and showed high correlation with CO (r=0.75). The relative contribution of biomass burning smoke to organic carbon was estimated from OC/EC ratios (organic carbon/elemental carbon) and elevated to 81.3% during the episode, indicating a significant impact on urban aerosol levels. The occurrence of high PM2.5/PM10 ratios (>0.80) and K(+)/EC ratios (>1.0), along with the increased carbonaceous concentrations and their fraction in PM2.5 (>40%) and high OC/EC ratios (about 8), could be used as immediate indicators for biomass burning pollution in cities. In addition, the heavy pollution involved a mixture of anthropogenic sources, reflected from the high SOR and NOR values and increases in the EFs (enrichment factors) of Mo, Zn, Cd, and Pb.

Vitamin D status and sun exposure in India

BACKGROUND

Little if any cutaneous production of vitamin D3 occurs at latitudes above and below 35° N and 35° S during the winter months. It was postulated that those residing in tropics synthesize enough vitamin D3 year round. Several studies have documented the effect of latitude, season and time of the day on the cutaneous production of vitamin D3 in an ampoule model. Studies from India have shown high prevalence of vitamin D deficiency despite abundant sunshine.

METHODS

We studied the influence of season and time of the day on synthesis of previtamin D3 in an ampoule model in Tirupati, (latitude 13.40° N and longitude 77.2° E) south India, between May 2007 to August 2008. Sealed borosilicate glass ampoules containing 50 μg of 7-DHC in 1 ml of methanol were exposed to sunlight hourly from 8 a.m. until 4 p.m. The percent conversion of 7-DHC to previtamin D3 and its photoproducts and the percent of previtamin D3 and vitamin D3 formed was estimated and related to solar zenith angle.

RESULTS

The percent conversion of 7-DHC to previtamin D3 and its photoproducts and formation of previtamin D3 and vitamin D3 was maximal between 11 a.m. to 2 p.m. of the day during the entire year (median 11.5% and 10.2% respectively at 12.30 p.m.).

CONCLUSIONS

Therefore at this latitude exposure to sunlight between the hours of 11 a.m. and 2 p.m. will promote vitamin D production in the skin year round.

Temporal variation of aerosol optical depth and associated shortwave radiative forcing over a coastal site along the west coast of India

Optical characterization of aerosol was performed by assessing the columnar aerosol optical depth (AOD) and angstrom wavelength exponent (α) using data from the Microtops II Sunphotometer. The data were collected on cloud free days over Goa, a coastal site along the west coast of India, from January to December 2008. Along with the composite aerosol, the black carbon (BC) mass concentration from the Aethalometer was also analyzed. The AOD0.500 μm and angstrom wavelength exponent (α) were in the range of 0.26 to 0.7 and 0.52 to 1.33, respectively, indicative of a significant seasonal shift in aerosol characteristics during the study period. The monthly mean AOD0.500 μm exhibited a bi-modal distribution, with a primary peak in April (0.7) and a secondary peak in October (0.54), whereas the minimum of 0.26 was observed in May. The monthly mean BC mass concentration varied between 0.31 μg/m(3) and 4.5 μg/m(3), and the single scattering albedo (SSA), estimated using the OPAC model, ranged from 0.87 to 0.97. Modeled aerosol optical properties were used to estimate the direct aerosol shortwave radiative forcing (DASRF) in the wavelength range 0.25 μm4.0 μm. The monthly mean forcing at the surface, at the top of the atmosphere (TOA) and in the atmosphere varied between -14.1 Wm(-2) and -35.6 Wm(-2), -6.7 Wm(-2) and -13.4 Wm(-2) and 5.5 Wm(-2) to 22.5 Wm(-2), respectively. These results indicate that the annual SSA cycle in the atmosphere is regulated by BC (absorbing aerosol), resulting in a positive forcing; however, the surface forcing was governed by the natural aerosol scattering, which yielded a negative forcing. These two conditions neutralized, resulting in a negative forcing at the TOA that remains nearly constant throughout the year.

Wet precipitation chemistry at a high-altitude site (3,326 m a.s.l.) in the southeastern Tibetan Plateau

This paper presents the results of wet precipitation chemistry from September 2009 to August 2010 at a high-altitude forest site in the southeastern Tibetan Plateau (TP). The alkaline wet precipitation, with pH ranging from 6.25 to 9.27, was attributed to the neutralization of dust in the atmosphere. Wet deposition levels of major ions and trace elements were generally comparable with other alpine and remote sites around the world. However, the apparently greater contents/fluxes of trace elements (V, Co, Ni, Cu, Zn, and Cd), compared to those in central and southern TP and pristine sites of the world, reflected potential anthropogenic disturbances. The almost equal mole concentrations and perfect linear relationships of Na(+) and Cl(-) suggested significant sea-salts sources, and was confirmed by calculating diverse sources. Crust mineral dust was responsible for a minor fraction of the chemical components (less than 15%) except Al and Fe, while most species (without Na(+), Cl(-), Mg(2+), Al, and Fe) arose mainly from anthropogenic activities. High values of as-K(+) (anthropogenic sources potassium), as-SO4(2-), and as-NO3(-) observed in winter and spring demonstrated the great effects of biomass burning and fossil fuel combustion in these seasons, which coincided with haze layer outburst in South Asia. Atmospheric circulation exerted significant influences on the chemical components in wet deposition. Marine air masses mainly originating from the Bay of Bengal provided a large number of sea salts to the chemical composition, while trace elements during summer monsoon seasons were greatly affected by industrial emissions from South Asia. The flux of wet deposition was 1.12 kg N ha(-1) year(-1) for NH4(+)-N and 0.29 kg N ha(-1) year(-1) for NO3(-)-N. The total atmospheric deposition of N was estimated to be 6.41 kg N ha(-1) year(-1), implying potential impacts on the alpine ecosystem in this region.

Atmospheric deposition of N, P and Fe to the Northern Indian Ocean: implications to C- and N-fixation

This study presents the first data set on atmospheric input of N, P and Fe to the Northern Indian Ocean. Based on the chemical analysis of ambient aerosols, collected from the marine atmospheric boundary layer (MABL) during the continental outflow (January-April), we document that dry-deposition fluxes (μmolm(-2) d(-1)) of N (2-167), P (0.5-4.8) and Fe (0.02-1.2) to the Bay of Bengal are significantly higher compared to those over the Arabian Sea [N: 0.2-18.6; P: 0.3-0.9; Fe: 0.001-0.015]. Using atmospherically derived P and Fe, C-fixation (1.1 Pg yr(-1)) in the Bay of Bengal is dominated by anthropogenic sources. In contrast, C-fixation (0.03 Pg yr(-1)) in the Arabian Sea is limited by P and Fe. This is attributed to the poor fractional solubility of atmospheric mineral dust transported to the Arabian Sea. However, N-fixation by diazotrophs in the two oceanic regions is somewhat similar (0.5 Tg yr(-1)). Our estimate of N-deposition (0.2 Tg yr(-1)) to the Northern Indian Ocean is significantly lower compared to model results (~800-1200 mg-Nm(-2)yr(-1)≈5.7-8.6 Tg yr(-1) by Duce et al. (2008); ~4.1 Tg yr(-1) by Okin et al. (2011); ~0.8 Tg yr(-1) by Kanakidou et al. (2012)). An overestimate of N-deposition by models could arise due to inappropriate parameterization of temporal variability associated with the continental outflow spread over only four months.

North-south cross sections of the vertical aerosol distribution over the Atlantic Ocean from multiwavelength Raman/polarization lidar during Polarstern cruises

Shipborne aerosol lidar observations were performed aboard the research vessel Polarstern in 2009 and 2010 during three north-south cruises from about 50°N to 50°S. The aerosol data set provides an excellent opportunity to characterize and contrast the vertical aerosol distribution over the Atlantic Ocean in the polluted northern and relatively clean southern hemisphere. Three case studies, an observed pure Saharan dust plume, a Patagonian dust plume east of South America, and a case of a mixed dust/smoke plume west of Central Africa are exemplarily shown and discussed by means of their optical properties. The meridional transatlantic cruises were used to determine the latitudinal cross section of the aerosol optical thickness (AOT). Profiles of particle backscatter and extinction coefficients are presented as mean profiles for latitudinal belts to contrast northern- and southern-hemispheric aerosol loads and optical effects. Results of lidar observations at Punta Arenas (53°S), Chile, and Stellenbosch (34°S), South Africa, are shown and confirm the lower frequency of occurrence of free-tropospheric aerosol in the southern hemisphere than in the northern hemisphere. The maximum latitudinal mean AOT of 0.27 was found in the northern tropics (0- 15°N) in the Saharan outflow region. Marine AOT is typically 0.05 ± 0.03. Particle optical properties are presented separately for the marine boundary layer and the free troposphere. Concerning the contrast between the anthropogenically influenced midlatitudinal aerosol conditions in the 30- 60°N belt and the respective belt in the southern hemisphere over the remote Atlantic, it is found that the AOT and extinction coefficients for the vertical column from 0-5km (total aerosol column) and 1-5km height (lofted aerosol above the marine boundary layer) are a factor of 1.6 and 2 higher at northern midlatitudes than at respective southern midlatitudes, and a factor of 2.5 higher than at the clean marine southern-hemispheric site of Punta Arenas. The strong contrast is confined to the lowermost 3km of the atmosphere.

Composition, seasonal variation, and sources of PM₁₀ from world heritage site Taj Mahal, Agra

Air samples for PM(10) (dp < 10 μm in aerodynamic diameter) were collected from March 2007 to February 2008 near Taj Mahal-a historically sensitive site in Agra. Each sample collected on 20.3 × 25.4-cm Whatman quartz microfiber filter using respirable dust sampler was analyzed gravimetrically for mass concentrations and chemically for elements such as Na, Mg, Al, Si, S, Ca, Sc, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Cd, Ba, and Pb by inductively coupled plasma atomic emission spectroscopy and inorganic ions such as NH (4) (+) , K(+), SO (4) (2-) , NO (3) (-) , F(-), and Cl(-) by ion chromatograph. Annual average of PM(10) 155.47 ± 77.97 μg/m(3) was three times high the annual average NAAQ standard of 50 μg/m(3) for sensitive area. PM(10) as well as K(+), Cl(-), As, and Pb were higher in winter while crust elements and secondary aerosols were higher in summer. The average equivalent ratio of NH (4) (+) to sum up of SO (4) (2-) and NO (3) (-) was greater than unity which indicates high source strength of ammonia and alkaline nature of aerosols in Agra. Source apportionment of PM(10) was carried out by factor analysis using principal component analysis (varimax rotated factor matrix method) of SPSS. Five sources contributing to PM(10) were identified as crust material, vehicular emissions, industrial emissions, coal and biomass burning, and secondary aerosols.

Vertical profiles of black carbon aerosols over the urban locations in South India

Vertical profiles of black carbon (BC) aerosol were determined from aircraft measurements under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) program conducted by the Indian Institute of Tropical Meteorology, India during 2009 over Bangalore and Hyderabad in south India. BC mass loadings decreased approximately monotonically from 10(3) to 10(4) ng/m(3) at the surface to ~10(2) ng/m(3) at an altitude of about 7 km; although layers at intermediate levels containing anomalously high BC loadings were frequently encountered that were attributed mainly to the convective transport from surface sources accompanied by changes in the local boundary layer and atmospheric stability. In addition, as evidenced from air mass back trajectories; long range transport from distant sources contributed to some anomalous spikes in BC concentration. The presence of BC in cloud forming regions of the free troposphere could have important implications for cloud microphysics and subsequent rainfall mechanism over this region. Apart from this, the effects on human health are equally important.

Mie lidar observations of lower tropospheric aerosols and clouds

Mie lidar system is developed at Laser Science and Technology Centre, Delhi (28.38°N, 77.12°E) by using minimal number of commercially available off-the-shelf components. Neodymium Yttrium Aluminum Garnet (Nd:YAG) laser operating at 1064nm with variable pulse energies between 25 and 400 mJ with 10 Hz repetition rate and 7ns pulse duration is used as a transmitter and off-axis CASSEGRAIN telescope with 100mm diameter as a receiver. Silicon avalanche photodiode (Si-APD) module with built-in preamplifier and front-end optics is used as detector. This system has been developed for the studies of lower tropospheric aerosols and clouds. Some experiments have been conducted using this set up and preliminary results are discussed. The characteristics of backscattered signals for various transmitter pulse energies are also studied. Atmospheric aerosol extinction coefficient values are calculated using Klett lidar inversion algorithm. The extinction coefficient, in general, falls with range in the lower troposphere and the values lie typically in the range 7.5×10(-5) m(-1) to 1.12×10(-4) m(-1) in the absence of any cloud whereas this value shoots maximum up to 1.267×10(-3) m(-1) (peak extinction) in the presence of clouds.