Sampling Frequencies for Determining Long-Term Average Concentrations of Atmospheric Participate Sulfates

Abstract

On the basis of simple statistical analysis preliminary conclusions and recommendations may be made on the ambient sampling strategy of particulate sulfates. The results are applicable to obtaining 24 hr average sulfate samples from high-volume particulate samplers. Two basic conclusions are: (1) A seasonally dependent sampling frequency appears desirable for sulfate monitoring. There are large seasonal variations during the warm months and relatively low and less variable values in the colder parts of the year. If one is interested only in the annual average, a constant sampling frequency of once every three days is allowable for a 90% confidence level. (2) To date, nearly all sulfate measurements available from the public domain are from exposed high-volume particulate filters. Federal and state routine sampling programs have largely followed the sampling rate of once every 6 days for total suspended particulates. Sulfate measurements are available from the National Air Sampling Network (NASN) at a frequency of once every 6 or 12 days. Annual or seasonal averages of sulfate concentrations derived from NASN stations in the midwest and northeast would not be acceptable in terms of this study. To obtain acceptable annual means from the NASN stations, it will be necessary to usemore » data for two or more years, provided the temporal distribution of sulfate concentrations is similar from year to year. Present knowledge of long-term sulfate variation is not complete enough to allow this assumption without qualification.« less