AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Organosulfates Formation in Secondary Organic Aerosol Produced from Photooxidation of Various VOCs In the Presence of NOx and Sulfuric Acid Aerosol Using Natural Sunlight
Jiaying Li, MYOSEON JANG, University of Florida
Abstract Number: 214 Working Group: Aerosol Chemistry
Abstract In this study, we hypothesized that the yields of organosulfates in the sulfuric acid seeded secondary organic aerosol (SOA) increase with the high concentrations of alcohols and aldehyde compounds in the SOA. To prove this hypothesis, organosulfates were produced via reactions of sulfuric acid aerosol with SOAs produced from the photooxidation of various volatile organic compounds (VOCs), such as isoprene, alpha-pinene, and toluene, in the presence of different NO$_x levels using an outdoor Teflon film chamber. The dialkylsulfates were quantified by the difference between the total sulfates that were estimated with a particle into liquid sampler ion chromatography (PILS-IC) and the inorganic sulfates estimated using the aerosol acidity data measured by a colorimetry integrated with a reflectance UV-Visible spectrometer (C-RUV). In this study, the yield of dialkylsulfates (Y$_(diOS-OC-SO$_4)) was described by normalizing the concentration of dialkylsulfate with both the total sulfate concentration and the OC concentration. The highest Y$_(diOS-OC-SO$_4) appeared in isoprene SOA and the lowest Y$_(diOS-OC-SO$_4) in alpha-pinene SOA. For all SOAs, the higher Y$_(diOS-OC-SO$_4) was observed under the higher NO$_x conditions, suggesting that carbonyls enhanced via RO$_2-NO chemistry under higher NO$_x levels react with sulfuric acid and form dialkylsulfates. To investigate the influence of aerosol compositions on Y$_(diOS-OC-SO$_4), the concentrations of functional groups in SOA were predicted using an absorptive partitioning of organic products between the gas (g), organic aerosol (or) and inorganic aerosol (in) phases. The concentration of organic products produced through gas phase photochemical reactions of VOCs were predicted using the explicit mechanisms (e.g., Master Chemical Mechanism) integrated with a kinetic solver. The aerosol functional group distributions predicted by the model were also compared to those estimated by the data obtained from a Fourier Transform Infrared (FTIR) spectrometer. Although the model predictions are limited to thermodynamic base SOA compounds, the overall trend in concentration of functional groups reasonably agrees with the FTIR data. The correlation between Y$_(diOS-OC-SO$_4) and the concentrations of functional groups in the SOA inorganic aerosol phase were analyzed, and results showed that the concentrations of –C-OH, -ONO2, and –C=O were strongly correlated to the Y$_(diOS-OC-SO$_4).