Rapid Nitrate Loss from PM10 Filters

As part of the California Air Resources Board's ongoing laboratory quality control and method validation program, researchers conducted comparative measurements of PM/sub 10/ nitrate and sulfate concentrations to demonstrate the equivalency of analytical procedures used in different laboratories. Surprisingly, the nitrate values measured after the six to eight months interim averaged 86% lower than those previously reported. The sulfate values stayed the same. This paper examines this rapid loss of nitrate from the PM/sub 10/ filters and the problems associated with using this method of measuring atmospheric nitrate.