While automated techniques exist for the integration of individual gas chromatograph peaks, manual inspection of integration quality and peak choice is still required due to drifting retention times and changing peak shapes near detection limits. The feasibility of a simplified method to obtain multiple bulk species classes from complex gas chromatography data is investigated here with data from the thermal desorption aerosol gas chromatograph (TAG). Chromatograms were divided into many "chromatography bins" containing total eluting mass spectra (both from resolved species and unresolved complex mixture [UCM]), instead of only integrating resolved peaks as is performed in the traditional chromatography analysis method. Positive matrix factorization (PMF) was applied to the mass spectra of the chromatography bins to determine major factors contributing to the observed chemical composition. PMF factors are not highly sensitive to the specific PMF error estimation method applied. Increasing the number of chromatography bins that each chromatogram was divided into improved PMF results until reaching 400 bins. Increasing the number of bins above 400 does not significantly improve the PMF results. This is likely due to 400 bin separation providing bin widths (4.6 s) that match the narrowest peak widths (4.8 s) of compounds found in the TAG chromatograms. The bin-based method took only a small fraction of the time to complete compared to peak-integrated method, significantly saving operator time and effort. Finally, high-factor solutions (e.g., 20 factors) of bin-based PMF can separate many individual compounds, homologues compound series, and UCM from chromatography data.

Abundant biomass is well accepted as a carbon-rich, sustainable, and renewable precursor for three-dimensional carbon materials, offering us a plethora of possibilities for energy conversion and storage as well as environmental treatments.

Abstract. The chemical complexity of biomass burning organic aerosol (BBOA) greatly increases with photochemical aging in the atmosphere, necessitating controlled laboratory studies to inform field observations. In these experiments, BBOA from American white oak (Quercus alba) leaf and heartwood samples was generated in a custom-built emissions and combustion chamber and photochemically aged in a potential aerosol mass (PAM) flow reactor. A thermal desorption aerosol gas chromatograph (TAG) was used in parallel with a high-resolution time-of-flight aerosol mass spectrometer (AMS) to analyze BBOA chemical composition at different levels of photochemical aging. Individual compounds were identified and integrated to obtain relative decay rates for key molecules. A recently developed chromatogram binning positive matrix factorization (PMF) technique was used to obtain mass spectral profiles for factors in TAG BBOA chromatograms, improving analysis efficiency and providing a more complete determination of unresolved complex mixture (UCM) components. Additionally, the recently characterized TAG decomposition window was used to track molecular fragments created by the decomposition of thermally labile BBOA during sample desorption. We demonstrate that although most primary (freshly emitted) BBOA compounds deplete with photochemical aging, certain components eluting within the TAG thermal decomposition window are instead enhanced. Specifically, the increasing trend in the decomposition m/z 44 signal (CO , typically attributed to freshly emitted BBOA in AMS field measurements, were also investigated. From the TAG chemical speciation and decomposition window data, we observed a decrease in m/z 60 with photochemical aging due to the decay of anhydrosugars (including levoglucosan) and other compounds, as well as an increase in m/z 60 due to the formation of thermally labile organic acids within the PAM reactor, which decompose during TAG sample desorption. When aging both types of BBOA (leaf and heartwood), the AMS data exhibit a combination of these two contributing effects, causing limited change to the overall m/z 60 signal. Our observations demonstrate the importance of chemically speciated data in fully understanding bulk aerosol measurements provided by the AMS in both laboratory and field studies.

Recent atmospheric field and modeling studies have highlighted a lack of understanding of the processes responsible for high levels of sulfate aerosol in the atmosphere, ultimately arising from a dearth of experimental data on such processes. Here we investigated the effect of temperature and simulated solar radiation on the catalytic oxidation of S(iv) to S(vi) (i.e., sulfite to sulfate) in aqueous suspensions of several metal-containing, atmospherically relevant particles including coal fly ash (FA), Arizona test dust (ATD) and an iron oxide (γ-FeO). The effect of temperature and light on S(iv) oxidation was found to be very different for these three samples. For example, in the presence of FA and γ-FeO the temporal evolution of dissolved Fe(ii) (formed via reductive particle dissolution) correlated with S(iv) oxidation. Accordingly, we propose that S(iv) oxidation in most of these systems initially occurs primarily at the particle surface (i.e., a heterogeneous reaction pathway), although a solution-phase (i.e., homogeneous) catalytic pathway also contributes over later timescales due to the formation and accumulation of dissolved Fe(iii) (generated via oxidation of dissolved Fe(ii) by O). It is likely that the homogeneous reaction pathway is operative at initial times in the presence of γ-FeO at 25 °C. In contrast, S(iv) oxidation in the presence of ATD appears to proceed entirely via a heterogeneous reaction, which notably does not lead to any iron dissolution. In fact, the greater overall rate of S(iv) loss in the presence of ATD compared to FA and γ-FeO suggests that other factors, including greater adsorption of sulfite, transition metal ion (TMI) catalysis by other metal ions (e.g., Ti), or different species of iron in ATD, play a role. Overall these studies suggest that the rate, extent and products of atmospheric S(iv) oxidation can be highly variable and dependent upon the nature of aerosol sources and ambient conditions (e.g., temperature and irradiance). Ultimately, such complexity precludes simple, broadly generalized schemes for this reaction when modeling atmospheric processes involving diverse components of different mineral dust aerosol as well as other metal-containing aerosol.