In-field ambient fine particle monitoring of an outdoor wood boiler: Public health concerns

Outdoor wood boilers (OWBs) are detached wood-fired units that heat water used for domestic consumption and heating. The increasing use of OWBs has prompted regulatory concern because of escalating public complaints. Few field studies of OWB ambient emissions have been conducted, limiting efforts to assess this air quality problem. A screening level evaluation was conducted to characterize ambient fine particle (PM2.5) levels nearby an OWB device and to overview operating and design factors that could influence PM2.5 levels. High hourly (186 µg/m3 4.3 h mean, 665 µg/m3 95th percentile) and peak continuous (8,880 µg/m3 15.5 avg) PM2.5 concentrations were found within 50–150 ft of an OWB relative to background levels throughout the course of nearly routine operating conditions. Values were highest during air intake within 1 h of fuel loading (416 µg/m3 1 h mean) compared to air-starved 22–24 h after loading (115 µg/m3 3.3 h mean). OWB features that could affect PM2.5 levels include exemption from federal wood stove standards, poor combustion design, large firebox capacity, trash burning use, low stack height, and four-season utility. In view of cardiac and respiratory health risks associated with transient exposure to ambient PM2.5 at levels well below those reported here, this pilot study contributes to the risk assessment field by identifying an emerging problem of potential public health significance. Key Words: air pollution, PM2.5, public health, outdoor wood boiler, residential wood combustion, wood smoke exposure