Spatial distribution of aerosol black carbon over India during pre-monsoon season

Aerosol black carbon (BC) mass concentrations ([BC]), measured continuously during a mutli-platform field experiment, Integrated Campaign for Aerosols gases and Radiation Budget (ICARB, March–May 2006), from a network of eight observatories spread over geographically distinct environments of India, (which included five mainland stations, one highland station, and two island stations (one each in Arabian Sea and Bay of Bengal)) are examined for their spatio-temporal characteristics. During the period of study, [BC] showed large variations across the country, with values ranging from 27 μg m^?3 over industrial/urban locations to as low as 0.065 μg m^?3 over the Arabian Sea. For all mainland stations, [BC] remained high compared to highland as well as island stations. Among the island stations, Port Blair (PBR) had higher concentration of BC, compared to Minicoy (MCY), implying more absorbing nature of Bay of Bengal aerosols than Arabian Sea. The highland station Nainital (NTL), in the central Himalayas, showed low values of [BC], comparable or even lower than that of the island station PBR, indicating the prevalence of cleaner environment over there. An examination of the changes in the mean temporal features, as the season advances from winter (December–February) to pre-monsoon (March–May), revealed that: (a) Diurnal variations were pronounced over all the mainland stations, with an afternoon low and a nighttime high; (b) At the islands, the diurnal variations, though resembled those over the mainlands, were less pronounced; and (c) In contrast to this, highland station showed an opposite pattern with an afternoon high and a late night or early morning low. The diurnal variations at all stations are mainly caused by the dynamics of local Atmospheric Boundary Layer (ABL). At the entire mainland as well as island stations (except HYD and DEL), [BC] showed a decreasing trend from January to May. This is attributed to the increased convective mixing and to the resulting enhanced vertical dispersal of species in the ABL. In addition, large short-period modulations were observed at DEL and HYD, which appeared to be episodic. An examination of this in the light of the MODIS-derived fire count data over India along with the back-trajectory analysis revealed that advection of BC from extensive forest fires and biomass-burning regions upwind were largely responsible for this episodic enhancement in BC at HYD and DEL.     

Scavenging of sea-salt aerosols by rain events over Arabian Sea during ARMEX

Scavenging coefficients are obtained for sea-salt particles at rainfall intensity of 5, 10, 15, 20 and 45 mm h⁻¹. Evolutions of size distributions for sea-salt particles by precipitation scavenging are simulated using theoretically estimated scavenging coefficients. Results indicate that below-cloud scavenging affects mainly sea-salt particles in coarse mode. Observed concentrations of Na⁺ and Cl⁻ in rainwater increased with rainfall intensity and aerosol size. Comparison of predicted concentrations of Na⁺ and Cl⁻ in rainwater with observed ionic concentrations of short-timed wet-only samples collected during rain events on 2 August 2002 over Arabian Sea (ARMEX-2002) supports the model result.     

Contribution of anthropogenic aerosols in direct radiative forcing and atmospheric heating rate over Delhi in the Indo-Gangetic Basin

Introduction  

The present work is aimed to understand direct radiation effects due to aerosols over Delhi in the Indo-Gangetic Basin (IGB) region, using detailed chemical analysis of surface measured aerosols during the year 2007.     

Study of aerosol transport through precipitation chemistry over Arabian Sea during winter and summer monsoons

Precipitation samples over the Arabian Sea collected during Arabian Sea Monsoon Experiment (ARMEX) in 2002–2003 were examined for major water soluble components and acidity of aerosols during the period of winter and summer monsoon seasons. The pH of rain water was alkaline during summer monsoon and acidic during winter monsoon. Summer monsoon precipitation showed dominance of sea-salt components (∼90%) and significant amounts of non-sea salt (nss) Ca²⁺ and SO₄²⁻. Winter monsoon precipitation samples showed higher concentration of NO₃⁻ and NH₄⁺ compared to that of summer monsoon, indicating more influence of anthropogenic sources. The rain water data is interpreted in terms of long-range transport and background pollution. In summer monsoon, air masses passing over the north African and Gulf continents which may be carrying nss components are advected towards the observational location. Also, prevailing strong southwesterly winds at surface level produced sea-salt aerosols which led to high sea-salt contribution in precipitation. While in winter monsoon, it was observed that, air masses coming from Asian region towards observational location carry more pollutants like NO₃⁻and nss SO₄²⁻ that acidify the precipitation.     

Chemical characteristics of free tropospheric aerosols over the Japan Sea coast: aircraft-borne measurements

Atmospheric aerosol particulate matter was directly collected in the free troposphere over the Japan Sea coast between 1992 and 1994 using an aircraft-borne nine-stage cascade impactor (particle size range: 0.1–8 μm). The water-soluble components in the aerosol particulate matter were analyzed by ion chromatography. Particulate sulfate and ammonium were detected in most of the samples and their size distributions showed noticeable peaks below the 1 μm particle size range. Water-soluble calcium (Ca²⁺) was detected in half of the samples; the size distribution showed that the maximum particle size was larger than 1 μm. Highly concentrated Ca²⁺ in larger particles was possibly due to transport of Kosa aerosols from the Asian continent in the free troposphere. The concentration of fine particulate sulfate and ammonium tended to increase whenever Ca²⁺ was detected, which suggests possible mixing of Kosa aerosols and non-Kosa aerosols during long-range transport of air masses containing Kosa particles.     

EPR investigations of Mn2+, Fe3+ ions and carbonaceous radicals in atmospheric particulate aerosols during their transport over the eastern coast of the English Channel

Electron paramagnetic resonance (EPR) spectroscopy was used to follow the evolution of the chemical forms of manganese and study other paramagnetic species in the atmospheric particulate aerosols at Wimereux, a French station located on the eastern coast of the English Channel. In parallel, Graphite Furnace Atomic Absorption Spectrometry (GFAAS) was used to measure the metal concentrations. Fe concentration values are common in North Sea sites, but those of Mn are quite higher due to the presence of an important local source of Mn. EPR spectra have evidenced isolated Fe³⁺ and Mn²⁺ ions and carbonaceous products with variable intensities according to the wind directions. Amounts of paramagnetic species and carbonaceous products are maximum for continental winds and minimum for marine winds. Three Mn types were identified depending on the sampling distance from the source of emission and the size of the particles.     

Number size distribution of atmospheric aerosols during ACE-Asia dust and precipitation events

Measurements of size-resolved particle number concentrations during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field campaign were made at the Gosan super-site, South Korea. In East Asia, dust and precipitation phenomena play a crucial role in atmospheric environment and climate studies because they are major sources and sinks of atmospheric aerosols, especially in the springtime. Total Ozone Mapping Spectrometer (TOMS) Aerosol Index and backward trajectories are analyzed to investigate the spatial and temporal evolution of dust storms. The size distributions between dust and non-dust periods and times with and without precipitation are compared. In order to understand the temporal evolution of the aerosol size distribution during dust and precipitation events, a simple aerosol dynamics model is employed. The model predicted and observed size distributions are compared with the measured data. The results show that the coarse mode particle number concentrations increase by a factor of 10–16 during dust events. During precipitation, however, particles in the coarse mode are scavenged by impaction mechanism. It is found that the larger particles are more efficiently scavenged. The degree of scavenged particle varies depending on the rainfall rate, raindrop size distribution and aerosol size distribution.     

The distribution of atmospheric sulphates in Canada and its relationship to long-range transport of air pollutants

Analyses of the distribution of airborne sulphates in Canada have been carried out using data obtained during April-May 1975. The present observations indicate that atmospheric sulphate loadings were relatively low ( < 5 μg m⁻³) in the Western Provinces while high values ( > 15 μg, m⁻³) were frequently observed in eastern Canada. The natural background level of ambient sulphates appeared to be less than 1.5 μg m⁻³ in Canada. However, maximum values ( > 20 μg m⁻³) were found to occur in southern Ontario. Generally, values recorded in the Atlantic Provinces were lower than the values observed in Ontario.The analyses indicate that the observed levels of sulphates could be associated with 3 types of typical weather situations : (a) extratropical cyclones, or on the forward sides of anticyclones with cold northerly flows (low sulphates); (b) on the rear sides of anticyclones (high sulphates); (c) quasi-stationary fronts (mixed). Air-parcel trajectory analyses of the low-level atmosphere show that high sulphate levels were often associated with S-SW airflows on the rear side of a warm moist air mass. The results suggest the long-range transport of airborne sulphur pollutants, mainly from several industrial areas in the U.S.A.     

Evidence for the "grasshopper" effect and fractionation during long-range atmospheric transport of organic contaminants

Although there is indisputable evidence that long-range atmospheric transport (LRAT) of organic contaminants occurs on a global scale, uncertainties remain about the detailed mechanism and extent of this phenomenon as well as the physical-chemical properties which facilitate LRAT. In this study, we discuss how mass balance models and monitoring data can contribute to a fuller understanding of the mechanism and extent of LRAT. Specifically we address the issues of "grasshopping" or "hopping" (the extent to which molecules are subject to multiple hops as distinct from a single emission-deposition event) and "global fractionation" (the differing behavior of chemicals as they are transported). It is shown that simple mass balance models can be used to assist the interpretation of monitoring data while also providing an instrument that can be used to assess the LRAT potential and the extent of hopping that organic substances may experience. The available evidence supports the notion that many persistent organic pollutants experience varying degrees of "hopping" during their environmental journey and as a consequence become fractionated with distance from source.     

Photochemical production and loss of organic acids in high Arctic aerosols during long-range transport and polar sunrise ozone depletion events

Unique daily measurements of water-soluble organics in fine (<2 μm) and coarse (>2 μm) aerosols were conducted at Alert in the Canadian Arctic in winter to spring of 1992. They yield insight into photochemical production and loss of organics during long-range transport and ozone depletion events following polar sunrise. Comprehensive analyses of α, ω-dicarboxylic acids (C₂–C₁₂), ω-oxocarboxylic acids (C₂–C₉) and α-dicarbonyls (C₂, C₃) as well as pyruvic acid and aromatic (phthalic) diacid were conducted using GC and GC/MS techniques. Oxalic (C₂) acid was generally the dominant diacid species in both fine and coarse fractions, followed by malonic (C₃) and succinic (C₄) acids. Concentrations of total diacids in the fine aerosol fraction (0.2–64 ng m⁻³) were 5–60 times higher than those in the coarse fraction (0.01–3 ng m⁻³). After polar sunrise in early-March, the total concentration of fine aerosol diacids increased by a factor of 3–5 while the coarse mode did not change significantly. From dark winter to sunlit spring, temporal changes in correlations and ratios of these water-soluble organics to vanadium and sulfate measured simultaneously suggest that atmospheric diacids and related organic compounds are largely controlled by long-range atmospheric transport of polluted air during winter, but they are significantly affected by photochemical production. The latter can occur in sunlight either during transport to the Arctic or during photochemical events associated with surface ozone depletion and bromine chemistry near Alert in spring. Conversion of gaseous precursors to particulate matter via photochemical oxidation was intensified at polar sunrise, resulting in a peak in the ratio of total diacids to V. During ozone depletion events, complex patterns are indicated in photochemical production and loss depending on the diacid compound. Unsaturated (maleic and phthalic) diacids were inversely correlated with particulate Br whereas saturated diacids (C₂–C₄) positively correlated with particulate Br. These results suggest that Br chemistry associated with ozone depletion leads to degradation of unsaturated diacids and to the production of smaller saturated diacids.     

长春供暖季室内外PM2.5浓度垂直分布与分析

为研究严寒地区供暖季室内外PM_(2.5)浓度的垂直分布,在供暖季分别对长春某高层居住建筑1、8、15、24、33楼层的室内外PM_(2.5)浓度进行监测,研究不同楼层室内外PM_(2.5)的浓度与变化特征。采用随机组分重叠模型(RCS)方法研究各楼层PM_(2.5)渗透因子,采用逐步回归分析方法研究室内PM_(2.5)浓度的各影响因素。结果表明:在供暖季,长春市高层建筑的不同楼层均存在一定的PM_(2.5)污染,室内外PM_(2.5)浓度随楼层升高大体呈现减小的趋势,但差异不显著。室内外PM_(2.5)浓度存在显著的相关性(P 0.05),在没有室内污染源时,室外颗粒物渗透是室内污染的主要来源。室内PM_(2.5)浓度与房间面积等没有显著相关性。     

Impact of dust storm on phytoplankton bloom over the Arabian Sea: a case study during March 2012

Environmental Science and Pollution Research - Dust storms affect the primary productivity of the ocean by providing necessary micronutrients to the surface layer. One such dust storm during March...     

Levels and distribution of heavy metals in atmospheric particular matters over the northern South China Sea

Oceans play a significant role in the cycling of trace metals and persistent organic pollutants. In this study, aerosol samples covering the whole northern South China Sea (SCS) were collected in 2005 and 2007, respectively, for analysis of trace metals and major elements. The levels of trace metals detected ranged from 0.514 to 119 ng/m³ in 2005 and from 0.130 to 24.2 ng/m³ in 2007, respectively. Cu, Zn, and Pb were the three predominant metals with high enrichment factors (>10), indicating the strong anthropogenic inputs. The trace metals over SCS were comparable to the values in suburban and background sites of South China, but generally higher than those over other seas and oceans. Considering the fact that they were influenced by their proximity to source regions and air mass origins, the elevated metals in 2005 were probably attributed to the strong wind and long-range atmospheric transport driven by Asian monsoon.     

Organochlorine pesticides in the atmosphere of Guangzhou and Hong Kong: Regional sources and long-range atmospheric transport

Organochlorine pesticides (OCPs) were measured in the atmosphere over the period of December 2003–December 2004 at four sampling sites in Guangzhou and Hong Kong. Gas phase and particle phase concentrations of 8 OCP species, including trans-chlordane (t-CHL), cis-chlordane (c-CHL), p,p′-DDT, p,p′-DDE, o,p′-DDT, α-endosulfan, α- and γ-hexachlorocyclohexane (HCH), were studied. OCPs were found predominantly in the gas phase in all seasons. t-CHL, c-CHL, o,p′-DDT, p,p′-DDT and α-endosulfan had significantly (p<0.001) higher concentrations than other OCPs, with mean values (gas+particle) typically ranging from 103 to 1440 pg m⁻³. In general, the concentrations of OCPs in summer were higher than that in winter, except for α-HCH which showed no clear seasonal pattern. Higher levels of γ-HCH and o,p′-DDT found in Guangzhou could be attributed to the present usage of lindane and dicofol in the Pearl River Delta (PRD) region. The very high concentrations of p,p′-DDT and α-endosulfan were observed at all sampling sites. The results of 7 days air back trajectory analysis indicated that the unusual high p,p′-DDT levels in summer in both cities could be related to the seasonal usage of DDT containing antifouling paints for fishing ships in the upwind seaports of the region. The high concentrations of α-endosulfan in winter in the study area suggested an atmospheric transport by the winter monsoon from the East China, where endosulfan is being used as insecticide in cotton fields. The consistency of the seasonal variation of concentrations and isomeric ratios of DDTs and α-endosulfan with the alternation of winter monsoon and summer monsoon suggested that the Asian monsoon plays an important role in the long-range atmospheric transport of OCPs.     

Organochlorine pesticides,polybrominated biphenyl ethers and lead isotopes during the spring time at the Waliguan Baseline Observatory,northwest China: Implication for long-range atmospheric transport

Located in the center of the Asian continent, the Waliguan Baseline Observatory (WBO) is the highest and the most inland Global Atmospheric Watch (GAW) station in the world. In the present study, organochlorine pesticides (OCPs) and polybrominated biphenyl (PBDEs) were analyzed in the daily collected samples at the WBO from 2 April to 23 May 2005, in an attempt to investigate the long-range atmospheric transport (LRAT) of persistent organic pollutants (POPs) in northwest China. The mean concentrations of OCPs at WBO were slightly higher than the Arctic regions, and the concentrations of total PBDEs (8.3±4.0 pg m⁻³) was comparable with other remote areas. The low temperature dependence of the POP concentrations in the air, and the absence of local use of these compounds implied LRAT to WBO. As suggested by backward air trajectory analysis, the high concentrations of γ-HCH, DDTs and PBDEs, during the sampled spring period, were mainly related to air mass passing over the neighboring countries (e.g., Russia, Kazakhstan). Additional evidence was also obtained by the lead isotopic composition analysis, which showed similar ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios as those of ores in these countries. The present results indicate that the WBO may serve as an excellent GAW station for monitoring the LRAT of POPs in the Asian continent.     

Carbonaceous and inorganic composition in long-range transported aerosols over northern Japan: Implication for aging of water-soluble organic fraction

To better understand the influence of sources and atmospheric processing on aerosol chemical composition, we collected atmospheric particles in Sapporo, northern Japan during spring and early summer 2005 under the air mass transport conditions from Siberia, China and surrounding seas. The aerosols were analyzed for inorganic ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and the major water-soluble organic compound classes (i.e., dicarboxylic acids and sugars). SO₄^2? is the most abundant inorganic constituent (average 44% of the identified inorganic ion mass) followed by NH₄⁺ (21%) and NO₃^? (13%). Concentrations of OC, EC, and WSOC ranged from 2.0–16, 0.24–2.9, and 0.80–7.9 μg m^?3 with a mean of 7.4, 1.0, and 3.1 μg m^?3, respectively. High OC/EC ratios (range: 3.6–19, mean: 8.7) were obtained, however WSOC/OC ratios (0.23–0.69, 0.44) do not show any significant diurnal changes. These results suggest that the Sapporo aerosols were already aged, but were not seriously affected by local photochemical processes. Identified water-soluble organic compounds (diacids + sugars) account for <10% of WSOC. Based on some marker species and air mass back trajectory analyses, and using stable carbon isotopic compositions of shorter-chain diacids (i.e., C₂–C₄) as photochemical aging factor of organic aerosols, the present study suggests that a fraction of WSOC in OC is most likely influenced by aerosol aging, although the OC loading in aerosols may be more influenced by their sources and source regions.     

Evaluating inter-continental transport of fine aerosols: (1) Methodology,global aerosol distribution and optical depth

Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black carbon (BC), organic carbon (OC), and mineral dust aerosols using a global coupled chemistry-aerosol model (MOZART-2) driven with NCEP/NCAR reanalysis meteorology for 1997–2003 and emissions approximately representing year 2000. The concentrations of simulated aerosol species in general agree within a factor of 2 with observations, except that the model tends to overestimate sulfate over Europe in summer, underestimate BC and OC over the western and southeastern (SE) U.S. and Europe, and underestimate dust over the SE U.S. By tagging emissions from ten continental regions, we quantify the contribution of each region's emissions on surface aerosol concentrations (relevant for air quality) and aerosol optical depth (AOD, relevant for visibility and climate) globally. We find that domestic emissions contribute substantially to surface aerosol concentrations (57–95%) over all regions, but are responsible for a smaller fraction of AOD (26–76%). We define “background” aerosols as those aerosols over a region that result from inter-continental transport, DMS oxidation, and emissions from ships or volcanoes. Transport from other continental source regions accounts for a substantial portion of background aerosol concentrations: 36–97% for surface concentrations and 38–89% for AOD. We identify the Region of Primary Influence (RPI) as the source region with the largest contribution to the receptor's background aerosol concentrations (or AOD). We find that for dust Africa is the RPI for both aerosol concentrations and AOD over all other receptor regions. For non-dust aerosols (particularly for sulfate and BC), the RPIs for aerosol concentrations and AOD are identical for most receptor regions. These findings indicate that the reduction of the emission of non-dust aerosols and their precursors from an RPI will simultaneously improve both air quality and visibility over a receptor region.     

Chemical fate,latitudinal distribution and long-range transport of cyclic volatile methylsiloxanes in the global environment: A modeling assessment

Cyclic volatile methylsiloxanes (cVMS) such as octamethycyclotetrasiloxane (D4), decamethycyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) are widely used as intermediates in the synthesis of high-molecular weight silicone polymers or as ingredients in the formulation of personal care products. The global environmental fate, latitudinal distribution, and long range transport of those cVMS were analyzed by two multimedia chemical fate models using the best available physicochemical properties as inputs and known persistent organic pollutants (POPs) and highly persistent volatile organic chemicals (“fliers”) as reference. The global transport and accumulation characteristics of cVMS differ from those of typical POPs in three significant ways. First, a large fraction of the released cVMS tends to become airborne and is removed from the global environment by degradation in air, whereas known POPs have a tendency to be distributed and persistent in all media. Secondly, although cVMS can travel a substantial distance in the atmosphere, they have little potential for deposition to surface media in remote regions. This contrasts with a deposition potential of known POPs that exceeds that of cVMS by 4–5 orders of magnitude. Thirdly, cVMS have short global residence times with the majority of the global mass removed within 3 months of the end of release. Global residence times of POPs on the other hand are in years. The persistent fliers resemble the cVMS with respect to the first two attributes, but their global residence times are more like those of the POPs.