Los Angeles summer midday particulate carbon: primary and secondary aerosol

Abstract

Aerosol sampling during photochemically active times
\nacross the Los Angeles Basin has provided evidence of
\nsecondary formation of organic aerosol from gas-phase
\nprecursors at midday. Ambient organic carbon/elemental
\ncarbon ratios exceeded the estimated ratio of organic
\ncarbon/elemental carbon in primary source emissions on
\nmost sampling days at all sites. The concentration of
\nsecondary organic aerosol was calculated by using ambient
\ndata and estimates of the organic carbon/elemental carbon
\nratio in primary source emissions. Nonparametric sign
\ncorrelations comparing calculated secondary organic carbon
\nconcentrations with tracers of both primary and secondary
\naerosols supported the method used to quantify
\nsecondary organic carbon. Secondary organic aerosol appears
\nto have contributed roughly half of the organic
\naerosol in Pasadena during midday summer conditions.