Scatter plot of ambient* PM
and indoor** concentrations (μg/m
), by season
† and home
‡ *Averages of PM2.5 24 h concentrations (μg/m3) at two sites (Villa Ada and ISS). **PM2.5 24 h indoor concentrations (μg/m3) in each home participating in the side validation study. †Spring = 1 and Winter = 2. ‡1 to 5.