Ambient air is sampled daily, with a nominal 24-hour sampling period, on a Canadian Air and Precipitation Monitoring Network (CAPMoN) sequential sample head located 10 meters above ground. Air is drawn through a three-stage filter pack consisting of 47-millimeter Teflon, nylon and cellulose filters. Particulate Cl-, NO3-, SO4=, NH4+, Na+, K+, Ca++ and Mg++ are collected on the Teflon filter, gaseous HNO3 and a small amount of SO2 are collected by the nylon filter, and gaseous SO2 and residual HNO3 are collected by the K2CO3-impregnated cellulose filter. Filter loadings determined by laboratory extraction and analysis are blank corrected and divided by calibrated sample air volume to get atmospheric concentration in micrograms per cubic meter at International Union of Pure and Applied Chemistry (IUPAC) standard temperature and pressure. The sampling and analysis methodology is described in Sirois and Fricke, 1992.