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India developed several industrial clusters nationwide, including in the state of Tamil Nadu to boost manufacturing. Three coastal cities, namely, Thoothukudi, Cuddalore, and Manali are developed as industrial clusters in Tamil Nadu. For the first time, we documented air quality trends in these industrial cluster cities of Tamil Nadu and compared them with those in Indian major cities, namely, Delhi, Mumbai, Kolkata, and Chennai. Between 2015-2020, data on key air quality parameters, such as particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), sulphur dioxide (SO2), and National Air Quality Index (NAQI) measured in these cities were analyzed. Our results suggest that the air quality parameters in coastal industrial cluster cities did not exhibit much seasonal variability owing to the influence of coastal meteorology compared to the hinterland cities, such as Delhi. Among the cities, Delhi showed the highest PM10, PM2.5, NO2 concentration levels, and NAQI, while Mumbai had the highest SO2 concentration levels. We observed that over the years, the concentration levels of NO2 were showing a decreasing trend in all the cities. While the concentration levels of PM10 (except, Mumbai, Chennai, and Kolkata), PM2.5 (except, Mumbai), SO2 (except, Kolkata), and NAQI (except, Mumbai, Manali, and Cuddalore) were showing a declining trend. The observed declining trend could be attributed to the air pollution reduction measures implemented in these cities. However, we also observed that many cities were in non-attainment of the National Ambient Air Quality Standards (NAAQS) for PM10 and PM2.5 but attained the NAAQS for NO2, except for a couple of years in Delhi and Kolkata. Whereas, all the cities attained the prescribed NAAQS for SO2. The findings of this study will serve as the baseline information for policymakers and air quality scientists interested in achieving clean air.

Accurate estimation of emissions of greenhouse gases (GHGs) is required for making effective climate change mitigation policies at the national level. Among major sources, municipal solid waste (MSW) is an important source of GHGs, such as methane (CH4), generated during the anaerobic decomposition of organic matter. In Viet Nam, the emissions of GHGs are not well quantified, in particular from the MSW management system. In this study, we estimated emissions of GHGs from the MSW management system of Ho Chi Minh City (HCMC), considering the current waste management practices. In HCMC, landfilling has been a common practice of solid waste management. About 85 percent of the total MSW generated in the city has been landfilled at two landfill sites. Our estimates show that landfilling was the significant source of GHGs in HCMC, with a net contribution of 781.05 kg CO2-equivalent (CO2-eq.) per tonne of MSW landfilled. From the whole MSW management system, the direct GHG emission was 768.61 (kg CO2-eq. per tonne of MSW) with avoided emissions of 72.47 (kg CO2-eq. per tonne of MSW) through composting and recycling of MSW. The net GHG emission from the MSW management system was 696.14 kg CO2-eq. per tonne of MSW (≈1.665 million tonnes of CO2-eq. per year). The GHG emission data of this study may be useful to policymakers for making effective climate change mitigation policies.