Understanding SOA formation and evolution through development and application of new analytical methods

Description

Our research foci are: 1) potential photochemical aerosol formation and chemical evolution for diverse environments and sources, 2) gas-particle partitioning thermodynamics and dynamics of bulk and chemically-speciated OA, and 3) development of analytical methods to extract, distill and interpret speciated and bulk chemical properties of complex high-resolution OA spectra. These different focus areas share the common theme that they aim to develop better understanding of SOA formation, composition, and evolution that can be used to test and improve model parameterizations of SOA and its climate-relevant properties. Our group has pioneered the field deployment of an oxidation flow reactor to obtain real-time field measurements of aerosol potential mass formation and chemical evolution from the key atmospheric oxidants (OH, O3, NO3). Results from urban and forested sites show that potential aerosol formation typically follows measureable gas-phase, diurnal or longer-term trends, and in some cases is much larger than predicted by SOA formation modeling. Typically for field observations of OH-driven chemistry, net SOA production is observed for the first few days of atmospheric equivalent aging, after which further oxidation results in loss of mass likely due to fragmentation and evaporation; whereas the degree of oxidation continues to increase. A newly-developed technique to quantify hundreds or acids in the gas and aerosol phases (MOVI-HRToF-CIMS) has allowed us to directly measure the gas-particle partitioning of individual and bulk organic acids. Bulk organic acids appear to follow absorptive partitioning and without major kinetic limitations. Ambient temperature, species carbon number and oxygen content control the volatility of organic acids and are good predictors for partitioning. Development of analytical methods to extract, distill and interpret bulk chemical properties and species concentrations of complex high-resolution mass and ion mobility spectra produced from the MOVI-HRToF-CIMS, an ion mobility spectrometer-CIMS, and other CIMS measurements has been a critical component of our research to produce meaningful information from these powerful but very complex techniques. Such efforts have focused on organic acid partitioning, estimates of the mass contribution of acids to total OA, and analysis of the composition and properties of ambient organic acid mixtures.