The first ever land campaign to study the spatial variability of the aerosol characteristics along the Brahmaputra river valley (BRV) in Assam, North-Eastern India, was conducted during 2011. Measurements were made ov...The first ever land campaign to study the spatial variability of the aerosol characteristics along the Brahmaputra river valley (BRV) in Assam, North-Eastern India, was conducted during 2011. Measurements were made over 13 locations for Aerosol Optical Depth (AOD), scattering coefficient, particulate matter, black carbon (BC) concentration and meteorological parameters. The BRV is divided into three sectors longitudinally viz western sector (WS), central sector (CS), and eastern sector (ES). Significant Spatial heterogeneity in AOD and BC concentration was observed (p < 0.05) with the highest values over WS and a continual decrease from WS to ES with aerosol dominance in PM2.5 category along the entire valley. The Angstrom coefficient measured using different wavelength pairs showed spatial variability indicating dominance of fine particles over WS and coarse particles in ES with a probable bimodal distribution. The scattering and absorption coefficient shows dominance of both types of aerosol over WS than other areas. The shortwave radiative forcing was higher over the WS than CS and ES of the valley. The campaign revealed that under favorable wind conditions, the BRV is loaded with significant amount of natural and anthropogenic aerosol during local winter and is influenced by the long-range transport of aerosols from the Indo-Gangetic plain.展开更多
Systematic monitoring of the fluctuations in atmospheric SO2 oxidation efficiency—measured as a molar ratio of SO42- to total SOx (SOx=SO2+SO42-), referred as S-ratio—have been performed during a major long range pl...Systematic monitoring of the fluctuations in atmospheric SO2 oxidation efficiency—measured as a molar ratio of SO42- to total SOx (SOx=SO2+SO42-), referred as S-ratio—have been performed during a major long range plume transport to northeast India (Shillong: 25.67°N, 91.91°E, 1064 m ASL) in March 2009. Anomalously low S-ratios (median, 0.03) were observed during the episode—associated with a cyclonic circulation—and the SO42- and SO2 exhibited unusual features in the ‘relative phase’ of their peaks. During initial days, when SO2 levels were dictated by the long range influx, the SO42- and SO2 variabilities were in anti-phase—for the differing mobility/loss mechanisms. When SO2 levels were governed by the boundary layer diurnality in the latter days, the anti-phase is explained by a ‘depleted OH level’—major portion being consumed in the initial period by the elevated SO2 and other pollutants. Simulations with a global 3D chemical transport model, GEOS-Chem (v8-03-01), also indicated ‘suppressed oxidation conditions’—with characteristic low S-ratios and poor phase agreements. The modelled OH decreased steadily from the initial days, and OH normalized to SO2—referred as OHspecific—was consistently low during the ‘suppressed S-ratio period’. Further, the geographical distribution of modelled OH showed a pronounced minimum over the region surrounding (20°N, 95°E) spanning parts of northeast India and the adjacent regions to the southeast of it—prevalent throughout the year, though the magnitude and the area of influence have a seasonality to it—with significant implications for reducing the oxidizing power of the regional atmosphere. A second set of measurements during January 2010—when prominent long range transports were absent—exhibited no anomalies, and the S-ratios were well within the acceptable limits (median, 0.32). This work highlights the GEOS-Chem model skill in simulating/detecting the ‘transient fluctuations’ in the oxidation efficiency, down to a regional scale.展开更多
文摘The first ever land campaign to study the spatial variability of the aerosol characteristics along the Brahmaputra river valley (BRV) in Assam, North-Eastern India, was conducted during 2011. Measurements were made over 13 locations for Aerosol Optical Depth (AOD), scattering coefficient, particulate matter, black carbon (BC) concentration and meteorological parameters. The BRV is divided into three sectors longitudinally viz western sector (WS), central sector (CS), and eastern sector (ES). Significant Spatial heterogeneity in AOD and BC concentration was observed (p < 0.05) with the highest values over WS and a continual decrease from WS to ES with aerosol dominance in PM2.5 category along the entire valley. The Angstrom coefficient measured using different wavelength pairs showed spatial variability indicating dominance of fine particles over WS and coarse particles in ES with a probable bimodal distribution. The scattering and absorption coefficient shows dominance of both types of aerosol over WS than other areas. The shortwave radiative forcing was higher over the WS than CS and ES of the valley. The campaign revealed that under favorable wind conditions, the BRV is loaded with significant amount of natural and anthropogenic aerosol during local winter and is influenced by the long-range transport of aerosols from the Indo-Gangetic plain.
文摘Systematic monitoring of the fluctuations in atmospheric SO2 oxidation efficiency—measured as a molar ratio of SO42- to total SOx (SOx=SO2+SO42-), referred as S-ratio—have been performed during a major long range plume transport to northeast India (Shillong: 25.67°N, 91.91°E, 1064 m ASL) in March 2009. Anomalously low S-ratios (median, 0.03) were observed during the episode—associated with a cyclonic circulation—and the SO42- and SO2 exhibited unusual features in the ‘relative phase’ of their peaks. During initial days, when SO2 levels were dictated by the long range influx, the SO42- and SO2 variabilities were in anti-phase—for the differing mobility/loss mechanisms. When SO2 levels were governed by the boundary layer diurnality in the latter days, the anti-phase is explained by a ‘depleted OH level’—major portion being consumed in the initial period by the elevated SO2 and other pollutants. Simulations with a global 3D chemical transport model, GEOS-Chem (v8-03-01), also indicated ‘suppressed oxidation conditions’—with characteristic low S-ratios and poor phase agreements. The modelled OH decreased steadily from the initial days, and OH normalized to SO2—referred as OHspecific—was consistently low during the ‘suppressed S-ratio period’. Further, the geographical distribution of modelled OH showed a pronounced minimum over the region surrounding (20°N, 95°E) spanning parts of northeast India and the adjacent regions to the southeast of it—prevalent throughout the year, though the magnitude and the area of influence have a seasonality to it—with significant implications for reducing the oxidizing power of the regional atmosphere. A second set of measurements during January 2010—when prominent long range transports were absent—exhibited no anomalies, and the S-ratios were well within the acceptable limits (median, 0.32). This work highlights the GEOS-Chem model skill in simulating/detecting the ‘transient fluctuations’ in the oxidation efficiency, down to a regional scale.
