Table 2: Distribution of home characteristics, surrounding land use, and questionnaire variables related to indoor air pollution.

From: Development of a modeling approach to estimate indoor-to-outdoor sulfur ratios and predict indoor PM2.5 and black carbon concentrations for Eastern Massachusetts households

 Percent urban spaces within 1 km2 grid (%)6727074100
 Major road density within 1 km2 grid (no. of vehicle·km/km2)
 Distance to central site (km)27.720.21.224.588.2
 Building age (years)62.831.99.051.0171.0
 No. of air conditioning2.
Use of forced air heating (# subject-week)YesNo
 (1) How many hours was the window open during sampling session?31.457.10.00.0168.0
 (2) How many hours did you use an electric space heater during sampling session?
 (3) How many hours did you use an air purifier during sampling session?
 (4) What fuel do you use for heating? (# homes)GasElectricOther/oil