Methylgloxal synthase, which catalyzes the conversion of dihydroxyacetone phosphate to methylglyoxal and inorganic phosphate, has been found in several Enterobacteriaceae. The enzyme along with glyoxalase I and II and D-lactate oxidase, therefore, constitute a nonphosphorylated shunt of the normal glycolytic pathway

Free radicals play a critical role in the formation of tropospheric air pollution, but current condensed chemical mechanisms used in gridded photochemical models under-predict total radical concentrations. This dissertation evaluates three hypotheses regarding radical sources and sinks using environmental chamber data and ambient data from southeast Texas. The first hypothesis, that aromatics chemistry is under-represented as a radical source in condensed chemical mechanisms, was evaluated mainly by using environmental chamber simulations and in part by using ambient simulations. Results indicate that improved characterization of aromatics chemistry in condensed chemical mechanisms will lead to more rapid and extensive free radical formation. The second hypothesis, that alkene reactions are under-represented as a radical source in condensed chemical mechanisms, was also evaluated using chamber data and TexAQS-2000 data. Results indicate that the methods used in mechanism condensation lead to lower estimates of free radical production than detailed, compound specific models. The third hypothesis, chlorine emissions and chemistry as a radical source, was also evaluated in a series of sensitivity analyses with various levels of molecular chlorine emissions. Results imply that incorporating chlorine chemistry in condensed chemical mechanisms is expected to lead to more accurate modeling of OH, HO₂ and O₃, particularly for the southeast Texas region where relatively large chlorine emissions occur from various anthropogenic sources of molecular chlorine. The relative magnitudes of these radical sources (aromatics, alkenes, and molecular chlorine) in southeast Texas were also compared using box modeling with TexAQS-2000 data. Results indicate that the relative importance of these three types of radical sources depends on the strengths of their corresponding emissions. / text

Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(¹D), O(³P), and O₃. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H₂O) and external OH reactivity (OHR_ext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(¹D), O(³P), and O₃ have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H₂O (< 0.1 %) or high OHR_ext ( ≥  100 s⁻¹ in OFR185 and > 200 s⁻¹ in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O₃, similarly to the troposphere. Working under low O₂ (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O₃ reactions even for the biogenic species most reactive with O₃. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 10¹³ and 1.5 × 10¹⁵ photons cm⁻² s⁻¹ at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.