Empirical correlations between black carbon aerosol and carbon monoxide in the lower and middle troposphere

Single-particle measurements of black carbon (BC) aerosol and simultaneous measurements of carbon monoxide (CO) were acquired aboard the NOAA WP-3D aircraft during the 2006 Texas Air Quality Study (TexAQS). Observed average BC mass loadings, estimated to account for ~90% of the ambient BC mass, decreased by more than 2 orders of magnitude from the polluted boundary layer to the clean middle troposphere (6 km). A strong positive, but non-linear, correlation was observed between simultaneous measurements of BC and CO. Based on an analysis of all the data below 1 km, we report a compact relationship between BC and CO with a slope of 5.8 ± 1.0 ng BC (kg dry air)-1 (ppb CO)-1 that is representative of regional urban and industrial emissions from Houston and Dallas. The BC/ CO emission ratio for a fresh biomass-burning plume was estimated at 9 ± 2 ng kg-1 ppb-1.