AEROSOL CHARACTERISTICS AT IDAHO-HILL DURING THE OH PHOTOCHEMISTRY EXPERIMENT

This paper supports other measurements at Idaho Hill by describing mea surements of the aerosol surface area, volume, and size distribution. The aerosol size distributions at the Idaho Hill site showed nuclei an d accumulation modes similar to other clean continental sites. However , there were fewer large aerosols. Principal components analysis verif ies that the modes present in the size distribution also had distinct time behavior. The coarse aerosol mode had two components with distinc tly different time behavior: aerosols larger than 2 mu m displayed a g reat deal of shortterm variability not present in smaller aerosols. Ac cumulation mode aerosols had separate correlations with fresh and aged pollution, whereas smaller aerosols were correlated only with fresh p ollution. Aerosols larger than 15 nm showed no diurnal variation in do wnslope conditions and an afternoon maximum in upslope conditions. Aer osol surface areas were too small to directly affect OH chemistry even if OH or HO2 had fast surface losses. Aerosol volumes indicate that a erosol nitrate is not a likely candidate to balance the NOy shortfall.