An Experiment with Air Purifiers in Delhi during Winter 2015-2016

Abstract

Particulate pollution has important consequences for human health, and is an issue of global concern. Outdoor air pollution has become a cause for alarm in India in particular because recent data suggest that ambient pollution levels in Indian cities are some of the highest in the world. We study the number of particles between 0.5μm and 2.5μm indoors while using affordable air purifiers in the highly polluted city of Delhi. Though substantial reductions in indoor number concentrations are observed during air purifier use, indoor air quality while using an air purifier is frequently worse than in cities with moderate pollution, and often worse than levels observed even in polluted cities. When outdoor pollution levels are higher, on average, indoor pollution levels while using an air purifier are also higher. Moreover, the ratio of indoor air quality during air purifier use to two comparison measures of air quality without an air purifier are also positively correlated with outdoor pollution levels, suggesting that as ambient air quality worsens there are diminishing returns to improvements in indoor air quality during air purifier use. The findings of this study indicate that although the most affordable air purifiers currently available are associated with significant improvements in the indoor environment, they are not a replacement for public action in regions like Delhi. Although private solutions may serve as a stopgap, reducing ambient air pollution must be a public health and policy priority in any region where air pollution is as high as Delhi’s during the winter.

Modeling the Impact of an Indoor Air Filter on Air Pollution Exposure Reduction and Associated Mortality in Urban Delhi Household

“…The indoor PM 2.5 exposure results from our study are consistent with prior studies that investigated indoor air filter use and air pollutant exposure, either by modeling [31,34] or field measurement [20,22,23,24]. Our study adds to the current evidence base by modeling the effects of air filters with different efficiencies and various user scenarios for a year, as well as by estimating mortality reduction.…”

“…Major sources of indoor PM 2.5 include cooking, smoking, and outdoor infiltration through windows and wall leakages. Indoor PM 2.5 removal mechanisms include deposition, exfiltration to outdoor air through exhaust fan(s), windows and wall leakage, and removal of PM 2.5 by a portable air filter device, which is commonly seen on the Indian market [23]. For cooking emissions, we used the PM 2.5 emission rate from the liquefied petroleum gas (LPG) stove use instead of biomass use [39], since Delhi has very high LPG coverage and traditional biomass only accounts for a small proportion of cooking energy in urban India [40,41].…”

“…The CADR rating system was used by American National Standards Institute (ANSI), indicating the volume of filtered air by an air-filtering device over time [48]. The portable air purifier of CADR 200 with HEPA filter represents the average level of dominant commercial air filters available on the Indian market; prices range between $250 and $1500 [23]. We also modeled air filters with lower efficiency to reflect lower-quality and more affordable air filter products.…”

“…Previous evidence in both developed [20,21] and developing countries [22,23] show that indoor PM 2.5 concentrations can be reduced effectively and substantially by using air filters. Such air filtration has also been shown to have cardiovascular and pulmonary health benefits [22,24], including reduced asthma symptoms and inflammation and improved airway mechanics [25].…”

“…Such air filtration has also been shown to have cardiovascular and pulmonary health benefits [22,24], including reduced asthma symptoms and inflammation and improved airway mechanics [25]. Several studies in India have investigated the effectiveness of HAP interventions on personal exposure to PM 2.5 and health benefits [26,27,28], and studies in urban Indian cities suggest that an air filter intervention alone cannot reduce personal exposure to PM 2.5 to the interim target guideline recommended by the World Health Organization (WHO) of 35 μg/m 3 [7,23]. This is mainly due to the dynamics of airborne contaminants and continued infiltration of ambient air pollution [29].…”