Air quality in major cities, especially Chennai, is slowly deteriorating with the city topping the State with high levels of particulate matter, both Respirable Suspended Particulate Matter (RSPM) and Total Suspended Particulate Matter (TSPM).

According to the Status Report of Air Quality in Tamil Nadu 2006-08 released by the Tamil Nadu Pollution Control Board (TNPCB), Chennai tops the list with five stations recording highest concentration of Respirable Suspended Particulate Matter (RSPM) in 2008.

While the Ministry of Environment and Forests has prescribed the annual average standard for RSPM as 60 microgram/cubic metre, Vallalar Nagar traffic intersection recorded 137.08 microgram/cubic metre followed by Anna Nagar at 132.17, T. Nagar at 119.92 and Tiruvottiyur industrial area at 86.92 microgram/cubic metre as annual mean concentration in 2008.

The TNPCB has also observed decreasing trend over the years in the number of stations confirming to the standard in the presence of RSPM, particles with less than 10 micron size.

During the year 2006, 61 per cent of the stations conformed to the standard in respect of annual average concentration of RSPM. In 2007, only 41 per cent stations conformed to the annual standard which further decreased to 36 per cent in 2008. That is, the level of RSPM exceeded the permissible limit in 14 out of 22 stations that year. Moreover, the TNPCB has found out that out of 14 stations exceeding the permissible limit in the presence of RSPM in 2008, the percentage violation was more than 60 per cent in 8 stations and 64 per cent of the stations were classified under high risk category (critical and high).

Similarly, the level of TSPM was also found high in Chennai. Out of the 8 stations in the city, 6 stations were present in the list of top 10 stations indicating the presence of dust particles (>10 micron size) in the ambient air.