The impacts and management of outdoor-sourced PM2.5 in New Delhi's buildings : a simulation approach

Abstract

New Delhi (and India more broadly) is noted for extremely high levels of ambient PM2.5, caused by a pattern of rapid urbanization and economic growth. As a large proportion of Indian buildings employ natural- or mixed-mode ventilation, and citizens in New Delhi spend up to 80% of their time indoors, the response of buildings to outdoor-sourced PM2.5 is a major, but relatively under-investigated concern. While much past work in this area has focused on characterizing indoor-outdoor pollutant concentration ratios under different conditions and studying the important question of exposure to cooking related PM2.5 emissions, building dynamical behavior, the feasibility of ventilation control strategies and air purification to reduce indoor PM2.5 concentrations have not been examined in detail. This gap is mirrored in the lack of enforcement of standards for indoor air quality and ventilation in India. In this work, a multi-zone building simulation program, CoolVent, is developed further to incorporate pollutant transport modeling and to consider the effects of urban environments on the driving mass transfer and heat exchange processes by using a mix of methods including a computational fluid dynamics approach to arrive at wind pressure coefficients. The adapted program and simulation framework is used to examine the behavior and performance of archetypal residential buildings in New Delhi and determine the efficacy of control strategies in reducing indoor PM2.5 levels to acceptable international standards. The results suggest that under representative conditions, buildings largely fail to provide healthy environments and hourly average indoor concentrations of PM2.5 closely follow ambient levels, which can exceed 300 [mu]g/m3. Under conditions of strict ventilation control, cooking-related ventilation, use of high efficiency particulate air filtration and limited infiltration through the building envelope, indoor PM2.5 levels may be limited below a threshold of 75 [mu]g/m3 even during periods of very high ambient pollutant concentrations. These findings have implications for building response and operation, urban and indoor air quality management and building codes. Options are discussed for policymakers to reduce exposure to PM2.5 within buildings and enable building occupants to manage their environments better. These span increasing access to appropriate filtration and low-cost air quality monitoring and information, and improvements to building codes. As ambient pollutant levels can be the primary drivers of indoor exposure to PM2.5 for large parts of a typical year, means for reducing PM2.5 emissions from a dominant source, vehicle exhaust, are evaluated.