Abstract:Size-resolved aerosol samples were collected both upwind and downwind of a large secondary road in the winter and spring of 2007 to assess contributions of on-road emissions to ambient aerosols. The aerosol samples were extracted and analyzed for a wide variety of organic compounds including polycyclic aromatic hydrocarbons (PAHs), alkanes, sugars, and organic acids. The results showed a strong seasonal pattern where the concentrations of most compounds were higher in winter than in spring. Some of the biogenic sugars were the exception, which might be the result of a “spring blooming season.” The surprising result was that the upwind site located in a residential neighborhood had very similar concentrations of most organic compounds compared to the near-roadway site. Possible reasons for the lack of differences in organic chemical concentrations between the near-road and control sites include: a large urban background concentration of aerosols superimposed on any local source; shifting wind directions that make the “downwind” site upwind during the night; and additional local sources in the residential neighborhood such as wood burning in winter.