Climatic influences on the spatial and temporal variability of aerosols across North America

Aerosols are a minor constituent of the Earth's atmosphere, yet they play an important role in the energy balance of the earth-atmosphere system. Despite their importance, the processes that determine the spatial and temporal variability of aerosols are not well understood. In this research, we evaluated climatic influences on aerosol variability across North America. Aerosol time series of at least three years duration from 27 AERONET and MFRSR monitoring stations formed the basis of our aerosol-climate analyses. Daily surface weather conditions, recorded at nearby synoptic weather stations, were classified into one of seven weather types using a hybrid classification procedure known as the Spatial Synoptic Classification (SSC) scheme. Aerosol optical depth (AOD) and Angstrom's wavelength exponent were then compared with the weather type.

In general, stations in the eastern seaboard region exhibited higher AOD than elsewhere, reflecting the influence of higher emissions of aerosols (or their precursors) in that region. We found a consistent relationship between AOD and SSC. At the majority of stations, AOD was highest during the Moist Tropical weather type and lowest during Dry Polar conditions. This explained the seasonal variability in AOD observed at most stations (maximum in summer, minimum in winter) since MT weather types are most frequent in summer and DP weather types are more common in winter. For those stations with little synoptic variability in AOD, AOD was low with little seasonal variability. Synoptic variability in Angstrom's exponent is less consistent than in AOD, though differences are noted.