Contribution of solid fuel, gas combustion or tobacco smoke to indoor air pollutant concentrations in Irish and Scottish homes.

There are limited data describing pollutant levels inside homes that burn solid fuel within developed country settings with most studies describing test conditions or the effect of interventions. This study recruited homes in Ireland and Scotland where open combustion processes take place. Open combustion was classified as coal, peat or wood fuel burning, use of a gas cooker or stove, or where there is at least one resident smoker. 24-hour data on airborne concentrations of particulate matter less than 2.5 microns in size (PM(2.5) ), carbon monoxide (CO), endotoxin in inhalable dust and carbon dioxide (CO(2) ), together with 2-3 week averaged concentrations of nitrogen dioxide (NO(2) ) were collected in 100 houses during the winter and spring of 2009-2010. The geometric mean of the 24-hour time-weighted-average (TWA) PM(2.5) concentration was highest in homes with resident smokers (99μg/m(3) - much higher than the WHO 24-hour guidance value of 25 μg/m(3) . Lower geometric mean 24-hour TWA levels were found in homes that burned coal (7 μg/m(3) ) or wood (6 μg/m(3) ) and in homes with gas cookers (7 μg/m(3) ). In peat-burning homes the average 24-hour PM(2.5) level recorded was 11 μg/m(3) . Airborne endotoxin, CO, CO(2) and NO(2) concentrations were generally within indoor air quality guidance levels.