Diurnal variability of fine-particulate pollution concentrations: data from 14 low- and middle-income countries.

Scientific understanding of indoor air pollution is predominately based on research carried out in cities in high-income countries (HICs). Less is known about how pollutant concentrations change over the course of a typical day in cities in low- and middle-income countries (LMICs). To understand how concentrations of fine particulate matter smaller than 2.5 microns in diameter (PM) change over the course of the day outdoors (across a range of countries) and indoors (using measurements from Dhaka, Bangladesh). Data on PM concentrations were gathered from 779 households in Dhaka as part of the MCLASS II (Muslim Communities Learning About Second-hand Smoke in Bangladesh) project, and compared to outdoor PM concentrations to determine the temporal variation in exposure to air pollution. Hourly PM data from 23 cities in 14 LMICs, as well as London (UK), Paris (France) and New York (NY, USA), were extracted from publicly available sources for comparison. PM in homes in Dhaka demonstrated a similar temporal pattern to outdoor measurements, with greater concentrations at night than in the afternoon. This pattern was also evident in 19 of 23 LMIC cities. PM concentrations are greater at night than during the afternoon in homes in Dhaka. Diurnal variations in PM in LMICs is substantial and greater than in London, Paris or New York. This has implications for public health community approaches to health effects of air pollution in LMICs.