I am consulting on a research project involving bridge decay. For this project we needed to locate a number of surface atmosphere chemical data (some sulfure oxides and chloride) as well as data on precipitation, snowfall, and min/max temperature.
Here are some sources we found:
- Cl, SO4, precipitation etc.: National Atmospheric Deposition Program, http://nadp.sws.uiuc.edu/ … the National Trends Network (NTN) data was the best
- SO2: http://www.epa.gov/airtrends/sulfur.html … a KML is even available from this link
- Snowfall, Min/max tempurature (precip is also available): Daily by state, http://cdiac.ornl.gov/ftp/ushcn_daily/, Monthly, http://cdiac.ornl.gov/ftp/ushcn_v2_monthly/