Aerosol indirect effect during successive contrasting monsoon seasons over Indian subcontinent using MODIS data

Aerosol indirect effect (AIE) was estimated over six Indian regions, which have been identified as main source regions of absorbing aerosol emissions, for four successive contrasting monsoon years, 2001 (normal monsoon rainfall year), 2002 (drought year), 2003 (excess monsoon rainfall year) and 2004 (below normal rainfall year). The AIE has been estimated both for fixed cloud liquid water path (CLWP) and for fixed cloud ice path (CIP) bins, ranging from 1 to 350 gm^?2 at 25 gm^?2 intervals obtained from Moderate resolution imaging spectroradiometer (MODIS). In 2002 and 2004, AIE found to be of positive (Twomey effect) in majority of the fixed CLWP and CIP bins, while in 2001 and 2003 majority of the bins were found to be showing negative indirect effect (Anti-Twomey effect). Changes in circulation patterns during contrasting monsoon seasons, bringing up air mass containing aerosols of different source origins may be the main reason for this positive and negative AIE. The study suggests that AIE could be one of the factors in modulating Indian summer monsoon. However, further research on this topic is to be carried out to establish the relationship between AIE and Indian monsoon rainfall and also AIE values may be parameterized in climate models for better prediction of monsoon.     

Assessment of emissions data for the Toronto region using aircraft-based measurements and an air quality model

An aircraft-based measurement campaign was conducted during the summer of 1996 in the vicinity of Toronto, Canada. The objective of the campaign was to assess the errors in a particular emission inventory used by three-dimensional air quality models. Measurements of NO₂ and hydrocarbons were made both upwind and downwind of Toronto, on days with strong synoptic-scale flow from a west to northerly direction. The chemical composition of the background airmass on these days was typical of unpolluted continental air. Measurements have been compared with the output from an on-line air quality model (MC2-AQ) run at 5 km resolution and suggest that emissions of NO_x from Toronto are well described in the emission database, though evidence that NO_x emissions are underestimated for suburban regions surrounding Toronto was found. In general, no significant underestimation of hydrocarbon emissions was found, though emissions of the model propane species, which includes acetylene and benzene, was underestimated by at least a factor of two.     

Understanding the contributions of anthropogenic and biogenic sources to CO enhancements and outflow observed over North America and the western Atlantic Ocean by TES and MOPITT

We investigate the effects of anthropogenic and biogenic sources on tropospheric CO enhancements and outflow over North America and the Atlantic during July–August 2006, the 3rd warmest summer on record. The analysis is performed using the 3D Regional chEmical trAnsport Model (REAM), satellite data from TES on the Aura satellite, MOPITT on the Terra satellite and surface monitor data from the SEARCH network. The satellite measurements of CO provide insight into the location of regional CO enhancements along with the ability to resolve vertical features. Satellite and surface monitor data are used to compare with REAM, illustrating model's ability to reproduce observed CO concentrations. The REAM model used in this study features CO emissions reduced by 50% from the 1999 EPA NEI and biogenic VOC emissions scaled by EPA-observed isoprene concentrations (20% reduction). The REAM simulations show large variations in surface CO, lower tropospheric CO and column CO, which are also observed by the surface observations and satellite data. Over the US, during July–August 2006, the model estimates monthly CO production from anthropogenic sources (5.3 and 5.1 Tg CO) is generally larger than biogenic sources (4.3 and 3.5 Tg CO). However, the model shows that for very warm days, biogenic sources produce as much CO as anthropogenic sources, a result of increased biogenic production due to warmer temperatures. The satellite data show CO outflow occurs along the East Coast of the US and Canada in July and is more broadly distributed over the Atlantic in August. REAM results show the longitudinally exported CO enhancements from anthropogenic sources (3.3 and 3.9 Tg CO) are larger than biogenic sources (2.8 and 2.7 Tg CO) along the eastern boundary of REAM for July–August 2006. We show that when compared with the impacts of both sources on increasing tropospheric CO exports, the relative impacts in August are greater than in July because of preferable outflow transport.     

Examination of dioxin fluxes recorded in dated aquatic-sediment cores in the Kanto region of Japan using multivariate data analysis

Past dioxin (coplanar polychlorinated biphenyl (Co-PCB), 2,3,7,8-substituted polychlorinated dibenzo-p-dioxin (PCDD) and 2,3,7,8-substituted polychlorinated dibenzofuran (PCDF)) fluxes recorded in dated aquatic-sediment cores were analyzed using principal component analysis (PCA). The data set consisted of samples from four cores collected from the Kanto region of Japan. Time trends and spatial differences in the dioxin flux were examined, and the potential relationship to emission sources was investigated. Twenty-five compounds and 58 core slices, corresponding to the later half of the 20th century, were subjected to the analysis. The PCA of both log-transformed and maximum-value-standardized data successfully divided the dioxin compounds into a small number of groups, and three similar clusters of Co-PCBs, PCDDs and penta- to hepta-CDFs were identified. PCB formulations used in the past are judged to have been responsible for the major part of the Co-PCB flux recorded in the sediment cores. However, the relationship to emission sources needs further investigation. It is suggested that most 2,3,7,8-substituted PCDDs and PCDFs are different from Co-PCBs in their emission sources or movements in the environment. The subcore clusters obtained from the PCA of log-transformed data show that the cores from different sampling areas exhibited distinct dioxin fluxes and compositions. Common time trends among the cores were more effectively summarized by the PCA of maximum-value-standardized data focusing on relative time trends. PC scores show that recently the flux of each dioxin compound in the four cores has been generally declining after having reached a peak.     

Catalytic reduction of sulfur dioxide with carbon monoxide over tin dioxide for direct sulfur recovery process

SO(2) reduction by CO over SnO(2) catalyst was studied in this work. The parameters were the reaction temperature, space velocity (GHSV) and [CO]/[SO(2)] molar ratio. The optimal temperature, GHSV and [CO]/[SO(2)] molar ratio were 550 degrees C, 8000 h(-1) and 2.0, respectively. Under these conditions, the SO(2) conversion and sulfur selectivity were about 78% and 68%, respectively. The following reaction pathway involving two mechanisms was proposed in SO(2) reduction by CO over SnO(2) catalyst: in the first step involving Redox mechanism, the elemental sulfur was produced by the mobility of the lattice oxygen between SO(2) and SnO(2) surface. In the second step, COS was formed by the side reaction between elemental sulfur and CO or metal sulfide and CO. In the third step involving COS intermediate mechanism, the abundant elemental sulfur was produced by the SO(2) reduction by COS which was produced in the second step and was more effective reducing agent than CO.     

Frequency distribution of pollutant concentrations over Indian megacities impacted by the COVID-19 lockdown

Environmental Science and Pollution Research - The megacities experience poor air quality frequently due to stronger anthropogenic emissions. India had one of the longest lockdowns in 2020 to curb...     

Characteristics of springtime profiles and sources of ozone in the low troposphere over northern Taiwan

To quantify the possible sources of the high ambient ozone concentration in the low troposphere over Taiwan, ozone sounding data from a two-year intensive field measurement program conducted in April and early May of 2004 and 2005 in northern Taiwan has been examined. We found that the vertical ozone distributions and occurrence of enhanced ozone in the lower troposphere (below 6 km) mainly resulted from (1)Type NE: the long-range transport of ozone controlled by the prevailing northeasterly winds below 2 km, (2)Type LO: the local photochemical ozone production process, and (3)Type SW: the strong southwest/westerly winds aloft (2–6 km). In the boundary layer (BL), where Asian continental outflow prevails, the average profile for type NE is characterized by a peak ozone concentration of nearly 65 ppb at about 1500 m altitude. For type LO, high ozone concentration with an average ozone concentration greater than 80 ppb was also found in the BL in the case of stagnant atmospheric and sunny weather conditions dominated. For type SW, significant ozone enhancement with average ozone concentration of 70–85 ppb was found at around 4 km altitude. It is about 10 ppb greater than that of the types NE and LO at the same troposphere layer owing to the contribution of the biomass burning over Indochina. Due to Taiwan's unique geographic location, the complex interaction of these ozone features in the BL and aloft, especially features associated with northeasterly and south/southwesterly winds, have resulted in complex characteristics of ozone distributions in the lower troposphere over northern Taiwan.     

High-resolution inventory of NO emissions from agricultural soils over the Ile-de-France region

Arable soils are a significant source of nitric oxide (NO), a precursor of tropospheric ozone, and thereby contribute to ozone pollution. However, their actual impact on ozone formation is strongly related to their spatial and temporal emission patterns, which warrant high-resolution estimates.Here, we combined an agro-ecosystem model and geo-referenced databases to map these sources over the 12 000 km² administrative region surrounding Paris, France, with a kilometric level resolution. The six most frequent arable crop species were simulated, with emission rates ranging from 1.4 kg N-NO ha⁻¹ yr⁻¹ to 11.1 kg N-NO ha⁻¹ yr⁻¹. The overall emission factor for fertilizer-derived NO emissions was 1.7%, while background emissions contributed half of the total NO efflux. Emissions were strongly seasonal, being highest in spring due to fertilizer inputs. They were mostly sensitive to soil type, crops' growing season and fertilizer N rates.     

Process analysis of ozone formation under different weather conditions over the Kanto region of Japan using the MM5/CMAQ modelling system

We have assessed the contributions of individual physical and chemical atmospheric processes on ozone formation under different weather conditions during a typical summer month (August 2005) using the MM5/CMAQ modelling system. We found that the ozone episodes in the Kanto region are dominated by three major patterns, of which Patterns I and II are regular summertime pressure patterns with a 26% and 16% frequency of occurrence, respectively. A process analysis at two typical sites in the Kanto region – one located in the central region of Tokyo and the other located in the rural areas of Kanto – indicates that ozone formation is mainly controlled by advection, vertical diffusion, dry deposition, and chemical processes. The ground-level ozone concentrations are enhanced mainly by the vertical mixing of ozone-rich air from aloft, whereas the dry deposition and chemical processes mainly deplete ozone. By investigating the effects of each process under different weather conditions, we found that the significant decrease in ozone removal due to the chemical and advection processes under conditions of high stagnation is the most important cause of the enhanced levels of ozone in the central region of Tokyo. The results of this study can contribute to a better understanding of ozone formation in the Kanto region, and they may be valuable for local policy makers for further development planning.     

Vertical profiles of ultrafine to supermicron particles measured by aircraft over Osaka metropolitan area in Japan

Intensive aircraft- and ground-based measurements of ultrafine to supermicron particles in the Osaka metropolitan area, Japan, were carried out on 17–19 March 2003, in order to investigate vertical profiles of size-resolved particles in the urban atmosphere. Differently sized particles were observed at different altitudes on 19 March. Relatively higher concentrations of ultrafine particles (31 nm) and submicron particles (0.3–0.5 μm) were measured (100–200 cm⁻³) at altitudes of 300 and 600 m, whereas supermicron particles (2–5 μm) were present (300–600 cm⁻³) at higher altitudes (1300 m in the morning and 2200 m in the afternoon). The chemical composition analysis showed that supermicron particles evidently comprised mainly soil particles mixed internally with anthropogenic species such as carbonaceous components and sulfate. Numerical simulation using the Chemical weather FORecasting System (CFORS) suggested the long-range transport of soil dust and black carbon from the Asian continent. Total number concentrations of particles sized 10–875 nm ranged from 4.8×10³ to 3.0×10⁴ cm⁻³ at an altitude of 300 m and from 7.3×10² to 4.8×10³ cm⁻³ at an altitude of 1300 m. Total number concentrations of particles sized 10–875 nm correlated very well with NO_X concentrations, and, therefore, ultrafine and submicron particles were likely emitted from urban activities such as car traffic and vertically transported. Number size distributions at lower altitudes obtained by aircraft measurements were similar to those obtained by ground measurements, with modal diameters of 20–30 nm on 18 March and about 50 nm on 19 March.     

Real-time wet scavenging of major chemical constituents of aerosols and role of rain intensity in Indian region

Real-time simultaneous studies on chemical characteristics of rainwater and PM₁₀ aerosols were carried out to understand the scavenging of major chemical components in Indian region. The concentrations of Ca²⁺, NH₄⁺, SO₄²⁻ and NO₃⁻ were observed to be lower in the aerosol samples collected during rain as compared to before and after rain events. The most significant reduction was noticed for Ca²⁺ (74%) during rain which showed highest scavenging ratio (SR) and indicated that below-cloud scavenging is an effective removal process for Ca²⁺ in Indian region. Among non-sea salt components, Ca²⁺ had highest SR at Hyderabad indicating typical characteristics of crustal influence as abundance of calcium carbonate in soil dust has been reported in India. However, the levels of these major chemical components gradually got build-up in due course of time. After rain events, the levels of SO₄²⁻ aerosols were noticed to be substantially higher (more than double) within 24 h. In general, scavenging ratios for all components (except Ca²⁺, NH₄⁺ and K⁺) were higher over BOB as compared to Hyderabad. The maximum fall in aerosol levels (BR minus AR) was observed during continuous and low intensity rain events that did not allow building up of aerosol concentrations.     

Influence of sea-land breezes on the tempospatial distribution of atmospheric aerosols over coastal region

The influence of sea-land breezes (SLBs) on the spatial distribution and temporal variation of particulate matter (PM) in the atmosphere was investigated over coastal Taiwan. PM was simultaneously sampled at inland and offshore locations during three intensive sampling periods. The intensive PM sampling protocol was continuously conducted over a 48-hr period. During this time, PM2.5 and PM(2.5-10) (PM with aerodynamic diameters < 2.5 microm and between 2.5 and 10 microm, respectively) were simultaneously measured with dichotomous samplers at four sites (two inland and two offshore sites) and PM10 (PM with aerodynamic diameters < or =10 microm) was measured with beta-ray monitors at these same 4 sites and at 10 sites of the Taiwan Air Quality Monitoring Network. PM sampling on a mobile air quality monitoring boat was further conducted along the coastline to collect offshore PM using a beta-ray monitor and a dichotomous sampler. Data obtained from the inland sites (n=12) and offshore sites (n=2) were applied to plot the PM10 concentration contour using Surfer software. This study also used a three-dimensional meteorological model (Pennsylvania State University/National Center for Atmospheric Research Meteorological Model 5) and the Comprehensive Air Quality Model with Extensions to simulate surface wind fields and spatial distribution of PM10 over the coastal region during the intensive sampling periods. Spatial distribution of PM10 concentration was further used in investigating the influence of SLBs on the transport of PM10 over the coastal region. Field measurement and model simulation results showed that PM10 was transported back and forth across the coastline. In particular, a high PM10 concentration was observed at the inland sites during the day because of sea breezes, whereas a high PM10 concentration was detected offshore at night because of land breezes. This study revealed that the accumulation of PM in the near-ocean region because of SLBs influenced the tempospatial distribution of PM10 over the coastal region.     

Annual and seasonal variability of ambient aerosols over an urban region in western India

Annual and seasonal variabilities in source contribution to total suspended particles (TSP) measured over an urban location in western India, Ahmedabad between May 2000 and January 2003 are examined in this study. Positive matrix factorization (PMF) resolved six factors including airborne regional dust, calcium carbonate rich dust, biomass burning/vehicular emissions, secondary nitrate/sulfate, marine aerosol, and smelter. In this study, non-parametric statistical tests including the Kruskal–Wallis analysis of variance (K–W ANOVA) and Spearman rank correlation (ρ) test were used to assess the annual and seasonal variations in factor contributions, and the influence of meteorology on these contributions, respectively. None of the factor contributions exhibited annual variations except airborne regional dust, and biomass burning/vehicular emissions factors. All of the factors exhibited seasonal variations. Several factor monsoon (July–September) median concentrations were significantly different from one or more of the other season medians. In general, it appeared that meteorological factors played a role in establishing the seasonal behavior of factor contributions. Factor contributions exhibited low to moderate correlations with meteorological parameters such as temperature, relative humidity, wind direction, and wind speed. Amongst all of the relationships, marine aerosol factor was reasonably well correlated with relative humidity (ρ = 0.73) and wind direction (ρ = 0.73) during the pre-monsoon season (March–May). This observation suggests that the aerosol transported by moisture laden winds from the Arabian sea contribute to this factor. The airborne regional dust factor was also moderately correlated with wind speed (ρ = 0.70) during the post-monsoon season. This relationship indicates that high regional dust concentrations are favored by high wind speeds and the resultant increase in dispersion.     

Multivariate data evaluation of PCB and dioxin profiles in the general population in Sweden and Spain

Thirty-three polychlorinated biphenyls and 20 dioxin-like congeners were determined by GC-MS in blood and adipose tissue samples from two general population groups, one in Spain (n = 35) and one in Sweden (n = 28). The results were evaluated by multivariate projection (Simca), after normalisation to the most abundant and stable congener in each data set, in order to reveal differences in the "national" congener profiles. The mean values of each population group did not differ significantly. The sum of PCBs in the Spanish was 1450 ng/g and in the Swedish 1310 ng/g. The sum of the dioxin-like compounds in Spain was 1180 pg/g and in Sweden 804 pg/g. The congener profiles differed between the countries. Mainly the higher chlorinated congeners for both the dioxin-like compounds and the PCBs are more dominant in the Spanish group compared to the Swedish.     

Source apportionment of the ionic components in precipitation over an urban region in Western India

Introduction  

Inorganic ion concentrations in event-based wet-only precipitation samples collected during the south-west (SW) monsoon at an urban location in Western India, Ahmedabad between July 2000 and September 2002 were measured by Rastogi and Sarin (2007).     

Bacterial community profiles from sediments of the Anacostia River using metabolic and molecular analyses

Background aim and scope  

Though the tidal Anacostia River, a highly polluted riverine system, has been well characterized with regard to contaminants, its overall resident bacterial populations have remained largely unknown. Improving the health of this system will rely upon enhanced understanding of the diversity and functions of these communities. Bacterial DNA was extracted from archived (AR, year 2000) and fresh sediments (RE, year 2006) collected from various locations within the Anacostia River. Using a combination of metabolic and molecular techniques, community snapshots of sediment bacterial diversity and activity were produced.     

An evaluation of the UAM-V predicted concentrations of carbon monoxide and reactive nitrogen compounds over the eastern United States during summer 1995

While there is a clear need to evaluate a photochemical model's ability in predicting not only the concentrations of O3, but also precursors and other trace species, many previous studies have focused only on the assessment of During the 1995 summer season, in addition to the routine monitoring of criteria pollutants, several research-oriented monitoring campaigns were conducted over the eastern United States, providing an extensive database of reactive nitrogen compounds, CO, and speciated hydrocarbon data. In this study, we examine the ability of a photochemical modeling system, RAMS/ UAM-V, to reproduce the measured concentrations of CO, NO2, and NOy over the region during the summer of 1995. The results demonstrate that there is agreement between modeled and measured seasonal average concentrations of NO2, both at the routine and research monitors. The same is true for NOy, but to a lesser degree. However, the model is found to significantly underpredict CO for the routine monitors in comparison to the research monitors.     

Multivariate toxicity profiles and QSAR modeling of non-dioxin-like PCBs--an investigation of in vitro screening data from ultra-pure congeners

The non-dioxin-like PCBs (NDL-PCBs) found in food and human samples have a complex spectrum of adverse effects, but lack a detailed risk assessment. The toxicity profiles of 21 carefully selected PCBs (19 NDL-PCBs) were identified by in vitro screening in 17 different assays on specific endpoints related to neurotoxicity, endocrine disruption and tumor promotion. To ensure that the test results were not affected by polychlorinated dioxins, dibenzofurans or DL-PCB contaminants, the NDL-PCB congeners were thoroughly purified before testing. Principal component analysis (PCA) was used to derive general toxicity profiles from the in vitro screening data. The toxicity profiles indicated different structure-activity relationships (SAR) and distinct mechanisms of action. The analysis also indicated that the NDL-PCBs could be divided into two groups. The first group included generally smaller, ortho-substituted congeners, comprising PCB 28, 47, 51, 52, 53, 95, 100, 101, 104 and 136, with PCB 95, 101 and 136 as generally being most active. The second group comprising PCB 19, 74, 118, 122, 128, 138, 153, 170, 180 and 190 had lower biological activity in many of the assays, except for three endocrine-related assays. The most abundant congeners, PCB 138, 153, 170, 180 and 190, cluster in the second group, and thereby show similar SAR. Two quantitative structure-activity relationship (QSAR) models could be developed that added information to the SAR and could aid in risk assessments of NDL-PCBs. The QSAR models predicted a number of congeners as active and among these e.g., PCB 18, 25, 45 and 49 have been found in food or human samples.     

The analysis of pollutant profiles by means of compositional analysis. An application to PCDD/F data

Compositional analysis consists of a group of techniques used to manipulate closed (=compositional) data, i.e. multivariate data summing to a fixed quantity (proportions, percentages). It is based on the analysis of the relations among variables and the use of logarithmic transformations. It has been claimed that this group of techniques should be used to analyse profiles of pollutant sources because profiles themselves are proportions. We show in this paper that, for the exploratory analysis of these data, a good strategy is to combine the analysis done with and without transformation because they give different and complementary insights on the structure of the data. We discuss in particular the study of processes such as the mixing of pollutants produced by different sources and the exponential decay of concentrations with distance to the source found in many studies. The clr transformation is also appropriate for the study of the variables having small proportions, which remain concealed by the abundant variables when analysed without transformation. We present simulations to illustrate these ideas and we also apply these techniques to two data sets of PCDD/F content in moss tissues.