Aerosol Properties. Hypothesis 5.1 Visibility in the area can be predicted from RH and size/composition information obtained from aerosol sizing instruments and size-resolved bulk chemistry instruments (MOUDI).
Aerosol Properties. The density of aerosol in the Pittsburgh area was found to be 1.5±0.5 g cm-3 (Xxxxxxxx et al., 2004). • Agreement within experimental error was obtained between the measured scattering coefficient and the calculations using the high temporal-resolution PM2.5 composition measurements and aerosol water content. Approaches relying on estimation of the aerosol water content tended to underpredict the scattering coefficient by around 20% (Xxxxxx et al., 2004c). • Aerosol sulfate and the associated water contribute around 70% to the scattering coefficient in the area during the summer with organics being responsible for most the remaining scattering. During the winter, sulfate accounts for approximately 40%, nitrate roughly 25%, and organics for 35% of the aerosol scattering (Xxxxxx et al., 2004c). • During the summer months the ambient aerosol practically always contained water even when the relative humidity was as low as 30%. In contrast, during the winter the aerosol was dry below 60% RH. The spring months were characterized by a transitional behavior between these two states. The observed seasonal behavior can be explained by the aerosol acidity. The summer aerosol was acidic and retained water at low RH. The winter aerosol was neutral and became wet when the relative humidity reached the deliquescence point of ammonium nitrate (Khlystov et al., 2005a).
