Closer home in Pune, experts said dust, vehicular emissions and industrial emissions are mostly responsible for the poor air quality. Pune also features among Maharashtra's worst-polluted cities in a recent World Health Organization (WHO) report.

The report on the air quality of urban areas compares various cities in the world. It said Pune has 92 micrograms per cubic metre of PM10, which is almost 1.5 times higher than the national ambient air quality standard of 60 micrograms per cubic metre. Although Pune's air quality fares better, the dust on the roads and that produced by construction cannot be ignored.

"The dust particles or particulate matter 10 is high in the city and above the prescribed level," Pune Municipal Corporation's environment officer MangeshDighe said. According to Indian Institute of Tropical Meteorology (IITM) data, the air pollution has increased by 35.7% since 2010.

"Pune is in the top five cities when we talk of lung diseases in the country. Although awareness has increased on air pollution and its ill-effects, a lot more needs to be done," chest physician Nitin Abhyankar said.

Shivajinagar, Hadapsar, Katraj, Lohegaon and Bhosari are polluted. Analysts say this may be due to heavy concentration of vehicles and industries in these areas.

A study by the IITM in collaboration with National Centre for Atmospheric Research (NCAR), Colorado, said that Maharashtra records 10% of the country's deaths due to pollution.

The state's most polluted cities, as per the WHO report, include Akola, Nagpur, Chandrapur, Jalgaon, Kolhapur Nashik, Amravati, Navi Mumbai, Mumbai and Pune. While PM10 is formed mostly of dust, PM2.5 particulate matter comes mostly from vehicular emissions.

Experts have noticed that although the air quality of Pune is better than Delhi and Mumbai, it is mostly 'moderate', it did have 'poor' air quality on certain days. "Pune city sees a lot of variation in the air quality. Colder temperatures lead to a rise in the air pollution as particulate matter hangs or remains suspended in the air. Hence, in the winter months, air pollution levels are recorded higher than the other months. Also, in the other months, during festivals like Diwali and New Year, the levels rise again and go into the moderate or poor category," a researcher with the System of Air Quality Forecasting and Research (SAFAR) project said.

In May and June, pollution levels are relatively lower than the other months. In Pune, the average concentration of PM2.5 in May this year was recorded as 38.02 and in Mumbai as 48.49 micrograms per cubic metre.

A senior scientist explained that permissible level of PM2.5 is 60 micrograms per cubic meter (ug/m3). Levels above that limit is a cause for concern, even if it lies in 'moderate' or 'poor' quality levels. High PM2.5 concentrations cause respiratory diseases like asthma and bronchitis. These particles can also penetrate deep into the lungs and blood stream.

Experts and doctors have expressed concern about the rising fine particulate matter. Sundeep Salvi, director of the Pune-based Chest Research Foundation, reiterates that regular exposure to such pollutants causes ischemic heart diseases.

The IITM report said there were around 2.5 lakh premature mortalities in 2011 due to exposure to PM2.5 and O3.