US EPA

Long term averages of the concentration of PM mass and components are of interest for determining compliance with annual averages, for developing exposure surrogated for cross-sectional epidemiologic studies of the long-term of PM, and for determination of aerosol sources by chemical mass balance for control strategy planning. In the U.S. compliance network, annual averages are frequently estimated from every-sixth-day measurements. In other countries annual averages may be estimated from other subsets such as from one week per month or two weeks per season. This paper investigates the error in the estimated annual average introduced by using every-sixth-day measurements or other less than every-day data.

Wilson, W. Error In Annual Average Due To Use Of Less Than Everyday Measurements. Presented at AWMA Speciality Conference , PM 2000, Charleston, SC, January 2000.