Spatial patterns of major aerosol species and selected heavy metals in the United States

Abstract

This paper focuses on the spatial variability of aerosol measurements from the IMPROVE (Interagency Monitoring of Protected Visual Environments) monitoring network. Spatial concentration trends of fine aerosol mass (PM 2.5) and five major aerosol species that comprise the bulk of fine mass for 3 years spanning 1993 through 1995 at 43 IMPROVE sites are presented. Using data from 62 monitoring sites spatial trends for select heavy metals for the years 1995 through 1998 are presented with the goal of lending insight to local versus regional sources of fine aerosol mass. The trace elements examined are arsenic, copper, zinc, selenium, lead, bromine, vanadium, and sodium that can be associated with industrial, agricultural, and mobile sources. Fine mass concentrations tend to be highest in the eastern United States and southern California with the lowest concentrations in the inter-mountain west. High concentrations of fine mass in the East are driven by ammonium sulfate concentrations, while in southern California ammonium nitrate is dominant; elsewhere carbonaceous species (light-absorbing carbon and organic mass) are about on par with sulfate as a contributor to fine mass. The trace element arsenic has its highest concentrations in the desert southwest. Zinc and copper show high concentrations in the desert southwest but have high concentrations in the eastern United States. Bromine concentrations are lowest in the Pacific Northwest with a local hot spot in southern California and an increasing trend to the eastern United States peaking in the Mid-Atlantic region. Lead and vanadium tend to be highest in the urbanized areas of the United States, which leads to elevated levels in southern California and much of the eastern United States.