Air pollution in city’s SRA houses 5 times more than nat’l limitUpdated: Dec 22, 2019 00:26 IST
Residents of low-income houses built in the city under the state’s Slum Rehabilitation Authority (SRA) scheme are exposed to high levels of indoor air pollution – similar to those living in slums – despite using low-emitting liquefied petroleum gas (LPG) cook stoves and electric lighting.
A first-of-its-kind study by a four-member research team led by professor Ronita Bardhan from Indian Institute of Technology, Bombay (IIT-B) , (now at University of Cambridge, UK) and Professor Leslie Norford from Massachusetts Institute of Technology, USA found indoor air pollution levels up to five times more than the national limit and 12 times more than international standards.
The analysis was conducted through field monitoring and surveys in 72 households in two SRA buildings (54 housing units) and Dharavi slums (18). It found indoor particulate matter of diameter less than 2.5 micrometers (PM2.5) in the range of 150-300micrograms per cubic metre (ug/m3). The Central Pollution Control Board has set 40ug/m3 and 60ug/m3 as the average annual and 24-hour permissible limit for PM2.5, respectively.
Guidelines by the World Health Organisation (WHO) recommend PM2.5 exposure not exceeding 25 μg/m3 over an average of 24 hours and mean annual of exposure 10ug/m3.
The study attributed indoor air pollution to poor interior design architecture (location of cook stoves and absence of cross-ventilation), infiltration of outdoor air inside the house and behaviour of the inhabitants (not operating exhaust fans during cooking and burning of incense sticks).
Researchers said their results challenge the belief that the quality of life for those who have shifted to rehabilitation architecture (high-rise SRA buildings) and gas cook stoves translate into enhanced natural ventilation and better household air quality than traditional dense slum clusters.
“We wanted to address indoor air quality problem of the upcoming affordable housing stock in India. As the model of SRA is now being replicated in the Pradhan Mantri Awas Yojana-Housing for All (Urban), it would be important to understand the efficacy (in term of environmental quality and health outcomes) of the new form of housing, where a majority of the future Indian urbanites will reside,” said Bardhan, university lecturer of sustainable Built Environment, University of Cambridge.
Maximum PM2.5 levels were in the range of 1390ug/m3 and 1741ug/m3 – 23 to 29 times CPCB levels and 55 to 69 times WHO levels – in the 54 surveyed SRA houses each measuring 240/300sqft.
Previous studies have estimated that over the past decade, household air pollution has resulted in 3.8–4.3 million premature deaths every year, with an estimated 1.5 million deaths occurring in India alone.
“For the first time, air exchange rates, which is a significant factor that determines the health impact of household air pollution and ventilation, inside SRA houses were measured. Larger the AER, the better it is. The slum households often have significantly larger air exchange rates than resettlement households,” said Bardhan.
Researchers said slum resettlement projects in Mumbai are often financially constrained; developers seek fast, low-cost designs that generally don’t employ central ventilation systems or High Efficiency Particulate Air (HEPA) filtration. “A house which is free, but the habitants pay high electricity bills and enormous medical expenses is not a free house,” said Bardhan.
The study ‘Indoor air quality among Mumbai’s resettled populations: Comparing Dharavi slum to nearby rehabilitation sites’ was published online in September, and will be printed in the January issue of journal Building and Environment.