Using Distributed Air Sampling to Distinguish Spatial Contributions of Woodsmoke from Other Particulate Sources in a Medium-Sized City

Abstract

During winter nights, woodsmoke from home heating may be a substantial source of air pollution in smaller cities and towns. In New Zealand towns with relatively little background air pollution, and substantial reliance on woodburning, we have the unique opportunity to examine spatial variance in woodburning-related pollution, and to disentangle its contribution from that of other sources (i.e., diesel). Few studies to date have been able to isolate spatial patterns in exposures during daytime and nighttime, nor to do so using woodsmoke-specific tracers (e.g., levoglucosan), to separate its contribution from that of other sources (e.g., diesel).We captured seven-day integrated samples of fine particulate matter (PM2.5), and elemental and organic tracers of woodsmoke and diesel emissions, during daytime and nighttime hours, across one city, over three weeks in early winter. At a subset of sites, we also sampled during hypothesized “peak” evening woodburning hours, to differentiate emissions during active residential woodburning, vs. overnight smoldering.Concentrations of PM2.5 were, on average, twice as high during nighttime than daytime. Much greater differences were observed, however, in woodsmoke-related tracers (e.g., levoglucosan, potassium) and indicators of treated- or painted-wood burning (e.g., arsenic, lead). Only nitrogen dioxide (NO2), calcium, iron, and manganese (common tracers of vehicular emissions) were higher during daytime. Levoglucosan and most PAHs were higher during “active” woodburning, vs. overnight smoldering.Our time-stratified spatial sampling approach detected substantial variability across the study area, and established a strong contribution of woodsmoke to nighttime PM2.5. Daytime vs. nighttime differences were greater than differences observed across sites. Traffic, especially diesel, contributed substantially to daytime NO2 and localized gradients in non-woodsmoke-related constituents.