Association between sea-land breeze and particulate matter in five coastal urban locations in India.

Particulate matter less than 2.5 µm particle diameter (PM2.5) is the most significant environmental issue globally. PM2.5 is an integral component of air quality monitoring and management, human health, weather, climate, and epidemiological research. In this work, we investigate the seasonal variation in PM2.5 mass concentrations and the association between the sea-land breeze system and particulate matter in five coastal urban locations in India (Kolkata, Visakhapatnam, Chennai, Thiruvananthapuram, and Mumbai). The relative occurrence of high PM2.5 mass concentrations was the greatest during the winter season (December through February) while the relative occurrence of low PM2.5 mass concentrations was the greatest during the monsoon season (June through September). Amongst locations, Kolkata experiences the highest PM2.5 loading in winter while Thiruvananthapuram experiences the lowest PM2.5 loading in monsoon. Indo-Gangetic Plain (IGP) outflow onto the Bay of Bengal significantly impacts locations along the eastern coast of India with reduced impact from north (Kolkata) to south (Chennai). The sea-breeze component analysis revealed daily cycles of the sea-land breeze with varying magnitudes of the breeze between the different seasons. Overall, we found a negative association between the sea-land breeze magnitude and PM2.5 mass concentrations, implying that the weakened sea-land breeze may deteriorate air quality in coastal locations due to poor ventilation. The vertical profiles of aerosol extinction showed elevated aerosol layers within 1 km from the surface in almost all locations. The decreasing trend in the land-sea temperature contrast in coastal locations is expected to deteriorate air quality in coastal locations in the warming future. Nevertheless, critical analyses using ground-based remote sensing techniques are required for a better understanding the impact of sea-land breeze dynamics on air quality in coastal locations.

Spatio-temporal variability of near-surface air pollutants at four distinct geographical locations in Andhra Pradesh State of India.

India is highly vulnerable to air pollution in the recent decade, especially urban areas with rapidly growing urbanisation and industrialisation. Here, we present spatio-temporal variability of air pollutants at four distinct locations in Andhra Pradesh State of India. The mean concentrations of air pollutants were generally higher at Visakhapatnam site than Amaravati, Rajahmundry, and Tirumala sites. The mean concentration of particulate matter of diameter less than 2.5 µm (PM2.5) was higher at Visakhapatnam site (48.5 ± 27.3 µg/m3) by a factor of about 1.6 as compared to Tirumala site (29.5 ± 17 µg/m3). On the contrary, the mean concentrations of oxides of nitrogen (NOx, 70.3 ± 28.1 µg/m3) and ammonia (NH3, 20.5 ± 9.2 µg/m3) were higher at Tirumala by a factor of about 1.4 and 1.9, respectively, as compared to Visakhapatnam (49 ± 5 µg/m3 and 10.7 ± 5 µg/m3). This was mainly attributed to higher vehicular emissions at Tirumala site. PM2.5, carbon monoxide (CO), NOx, and sulfur dioxide (SO2) showed distinct seasonal variation, with higher concentrations in winter followed by post-monsoon, pre-monsoon and monsoon. The Concentration Weighted Trajectory analysis of PM2.5 based on 5-days backward air mass trajectories showed that all sites experienced northeast air mass flow indicative of the outflow from Indo-Gangetic Plain, particularly in the post-monsoon and winter seasons. The Continuous Wavelet Transform analysis further showed that higher variations in PM2.5 concentrations occurring at a regular interval from a week to 16 days at both Tirumala and Visakhapatnam sites, while weekly periods are dominant over Amaravati and Rajahmundry sites with 95% significance during post-monsoon and winter seasons. Overall, our results underline heterogeneity in air pollution emission sources and influx of pollutants from distant sources, which would be useful when formulating the policies and mitigation procedures for this region.

Assessment of aerosol optical and micro-physical features retrieved from direct and diffuse solar irradiance measurements from Skyradiometer at a high altitude station at Merak: Assessment of aerosol optical features from Merak.

Optical and micro-physical features of aerosol are reported using Skyradiometer (POM-01L, Prede, Japan) observations taken from a high-altitude station Merak, located in north-eastern Ladakh of the western trans-Himalayas region during January 2011 to December 2013. The observed daily mean aerosol optical depth (AOD, at 500 nm) at the site varied from 0.01 to 0.14. However, 75 % of the observed AOD lies below 0.05 during the study period. Seasonal peaks of AOD occurred in spring as 0.06 and minimum in winter as 0.03 which represents the aged background aerosols at the site. Yearly mean AOD at 500 nm is found to be around 0.04 and inter-annual variations of AOD is very small (nearly ±0.01). Angstrom exponent (a) varied seasonally from 0.73 in spring to 1.5 in autumn. About 30 % of the observed a lies below 0.8 which are the indicative for the presence of coarse-mode aerosols at the site. The station exhibits absorbing aerosol features which prominently occurred during spring and that may be attributed by the transported anthropogenic aerosol from Indo-Gangatic Plain (IGP). Results were well substantiated with the air mass back-trajectory analysis. Furthermore, seasonal mean of single scattering albedo (SSA at 500 nm) varied from of 0.94 to 0.98 and a general increasing trend is noticed from 400 to 870 nm wavelengths. These features are apparently regional characteristics of the site. Aerosol asymmetry factor (AS) decreases gradually from 400 to 870 nm and varied from 0.66 to 0.69 at 500 nm across the seasons. Dominance of desert-dust aerosols, associated by coarse mode, is indicated by tri-modal features of aerosol volume size distribution over the station during the entire seasons.

An early South Asian dust storm during March 2012 and its impacts on Indian Himalayan foothills: a case study.

The impacts of an early South Asian dust storm that originated over the western part of the Middle East and engulfed northwest parts of India during the third week of March 2012 have been studied at four different stations covering India and Pakistan. The impacts of this dust storm on aerosol optical properties were studied in detail at Delhi, Jodhpur, Lahore and Karachi. The impact could also be traced up to central Himalayan foothills at Manora Peak. During dust events, the aerosol optical depth (AOD) at 500 nm reached a peak value of 0.96, 1.02, 2.17 and 0.49 with a corresponding drop in Ångström exponent (AE for 440-870 nm) to 0.01, -0.02, 0.00 and 0.12 at Delhi, Jodhpur, Lahore and Karachi, respectively. The single scattering albedo (SSA) at 675 nm was relatively lower at Delhi (0.87) and Jodhpur (0.86), with absorption Ångström exponent (AAE) less than 1.0, but a large value of SSA was observed at Lahore (0.98) and Karachi (0.93), with AAE value greater than 1.0 during the event. The study of radiative impact of dust aerosols revealed a significant cooling at the surface and warming in the atmosphere (with corresponding large heating rate) at all the stations during dust event. The effect of this dust storm was also seen at Manora Peak in central Himalayas which showed an enhancement of ~28% in the AOD at 500 nm. The transport of dust during such events can have severe climatic implications over the affected plains and the Himalayas.