People living near Bandra's Kherwadi and Sion Hospital intersections are at a greater risk of developing health problems because of high pollution levels, whereas Airoli residents breathe some of the cleanest air in Maharashtra, according to a new study.

The concentrations of respirable suspended particulate matter (RSPM) and nitrogen oxides (NOx) measured in the two city areas, which see severe traffic congestion, were way above the standard limits in 2016-17.

Particulate matter is a mix of tiny particles -dust, soot, smoke -that can enter the lungs and cause a broad range of health complications. NOx can trigger breathing difficulties.

An air-quality monitoring station in Bandra recorded an annual average RSPM concentration of 125 micrograms per cubic metre (gm3) against the standard limit of 60 g m3, while the average level in Sion was 150 gm3.

The annual average levels of nitrogen oxides for Bandra and Sion during the same period were 48 gm3 and 78 gm3, respectively, against the standard limit of 40 gm3.

The Maharashtra Pollution Control Board conducted the statewide study on air quality and the report was prepared by The Energy and Resources Institute (TERI). The data from 74 air quality monitoring stations across the state was used. According to the report, the air quality in Bandra and Sion often fell in the "poor category". Except Airoli, all other monitoring stations reported annual average RSPM levels which were higher than normal.

"The high RSPM concentrations in Sion and Bandra are attributed to emissions from industries, construction sector, and vehicles," said Prathmesh Chourey, a fellow of TERI, Western Regional Centre. "The stone quarrying work at Mahape, Turbhe, and Uran also have an effect on Mumbai as the particulate matter gets carried by wind and sea breeze."

The amount of particulate matter from sites such as mines and quarries can be reduced through good operation and maintenance practices involving the use of water mists and wind screens, he added. Stricter norms are needed for the construction sector, a major contributor of air pollution.

The Sion monitoring station has been consistently recording high concentrations of nitrogen oxides for the past seven years. "The NOx levels are relatively higher in Mumbai because of dense traffic and vehicular emissions. It is the main cause of bronchitis in asthmatic children," Chourey said. "The NOx levels in Thane are showing a decreasing trend because the municipal corporation there has completed road works."

Airoli's air quality has improved because the lease period of quarries expired in September last year and stone quarrying has stopped in the region. "The state pollution control has taken many initiatives in Navi Mumbai. Factories have switched to gas-fired boilers instead of using furnace oil and light diesel," he said.