Weekly patterns of aerosol in the United States
1Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA
2Vanderbilt University, Nashville, TN 37240, USA
3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
4Crocker Nuclear Laboratory, University of California, Davis, Davis, CA 95616, USA
*now at: School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
Abstract. Data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network of aerosol samplers and NOAA monitoring sites are examined for weekly cycles. Fine particle elemental carbon, crustal elements, and coarse particle mass had pronounced (up to 20%) weekly cycles with minima on Sunday or Monday. Fine particle organic carbon and mass had smaller amplitude cycles, also with Sunday or Monday minima. There was no statistically significant weekly cycle in fine particle sulfate despite a 10 to 15% weekly cycle in power plant SO2 emissions. Although results for nitrate must be treated with caution, it showed a pronounced weekly cycle with an amplitude similar to elemental carbon. The only species found with a weekend maximum was Pb, probably from general aviation on weekends. Aerosol optical properties at NOAA monitoring sites were consistent with the IMPROVE chemical data, with significant weekly cycles in aerosol light absorption but not light scattering. These results support a large role of diesel emissions in elemental carbon aerosol over the entire United States and suggest that a large fraction of the airborne soil dust is anthropogenic. They also suggest that studies of weekly cycles in temperature, cloudiness, or precipitation should look for causes more in light-absorbing particles and dust rather than sulfate or total aerosol. There are also implications for personal exposure and epidemiological studies of aerosol health effects.