Aerosol Chemical Composition Characterization During the 2000 Texas Air Quality Study

During the DOE G-1 aircraft flights in TexAQS 2000, the inorganic ionic component of fine aerosol particles (diameter < 2.5 μm) was determined using a particle-into-liquid-sampler coupled to ion chromatography analysis, yielding concentrations of nitrate, sulfate, ammonium, sodium, calcium and potassium at a 3-min time resolution and a limit of detection of ~0.1 μg m^-3. Black carbon was determined using a particle soot absorption photometer. The total aerosol mass was estimated from the particle size/number distribution determined using a passive cavity aerosol spectrometer probe and an assumed density. The aerosol organic fraction was taken as the difference between the total aerosol mass and the sum of the ionic species and black carbon. The median concentrations of the total aerosol mass and total ionic species measured for the 17 flights varied between 3 and 30 and 2 and 10 μg m^-3, respectively. The interquartile range of the organic fraction for the entire study was between 20 and 60 percent. Although the organic component exhibited a strong correlation with black carbon, it only showed a weak correlation with photochemical products such as ozone and formaldehyde. Relationships between organic aerosol mass loading and photochemistry will be investigated to examine the contributions of photochemistry and different VOC source categories, namely, traffic, industrial and biogenic, to the formation of organic aerosols.