1. Effects of environmental variables and sampling media on the collection of atmospheric sulfate and nitrate;Appel;Final Report to the California Air Resources Board,1978
2. Interference effects in sampling particulate nitrate in ambient air;Appel;Atmospheric Environment,1979
3. Improvement and evaluation of methods for sulfate analysis—II;Appel;Final Report for EPA. Grant No. 805-447-1. EPA Report 600/4-80-024,1980
4. Sampling of nitrates in ambient air;Appel;Atmospheric Environment,1981
5. Sampling of carbonaceous particles in the atmosphere;Appel;Atmospheric Environment,1983