Wednesday, 16 January 2002
Relationships between Particle Size and Composition, Photochemical Production of Secondary Aerosol, and New Particle Formation in Houston
An Aerodyne Aerosol Mass Spectrometer was deployed at the La Porte ground site in the Houston metropolitan area during the TEXAQS 2000 study. The AMS monitored the aerosol mass signal for m/z peaks 1-300 of the mass spectrometer and the size distribution of about 20 selected m/z. The joint evolution of the aerosol mass signal in particle size and time can be used to classify the m/z into separate chemical components and to identify possible interferences. At least 6 aerosol species or groups of species were identified using this technique, including sulfate, nitrate, ammonium, and at least three different types of organic aerosols. A strong diurnal cycle was observed for some of the aerosol organic species. These species appeared on the surface area mode of the aerosol and correlated with photochemical indicators such as OH, HO2, and PANs. Likely these are secondary organic aerosol species being produced photochemically and then nucleating or being taken up by the preexisting aerosol. Finally, a fine aerosol mode was observed several afternoons with the AMS and a collocated SMPS that is consistent with new particle formation. These particles contain mostly sulfate and organics.