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6025994 
Dissertation 
Formaldehyde as a probe of rural volatile organic compound oxidation 
Digangi, JP 
2012 
Ann Arbor 
The University of Wisconsin - Madison 
ProQuest Dissertations and Theses 
2012 
English 
Formaldehyde (HCHO), one of the most common organic species present in the atmosphere, is produced via the atmospheric oxidation of volatile Organic compounds (VOCs). Byproducts of VOC oxidation include tropospheric ozone and secondary organic aerosol, both of which are correlated with increased incidences of cardiac/respiratory disease and mortality. Accurate models are crucial to predicting these species' behavior and require an accurate understanding of the mechanisms of VOC oxidation. Oxidized VOCs (OVOCs), produced as intermediates in VOC oxidation, can illustrate the chemical pathways involved. Measurement/model comparisons of VOC oxidation in rural environments (e.g. forests) have typically reported poor agreement, complicated by the advection of polluted anthropogenic air. Forest photochemical measurements have also implied the emission of unmeasured biogenic VOCs (BVOCs). specifically terpenes. As HCHO is an OVOC produced in the oxidation of nearly all VOCs, comparisons of measured and modeled HCHO concentrations can illustrate the accuracy with which models reproduce the overall VOC oxidation chemistry. To address these issues, a new HCHO detection technique was developed, Fiber Laser-Induced Fluorescence (FILIF). FILIF is capable of faster sampling rates (10 Hz) than previously reported with comparable limits of detection to literature methods (∼25 ppt, in 1 s). Using FILIF, HCHO concentration gradients and vertical fluxes were measured in a coniferous forest canopy during BEACHON-ROCS 2010. Ground litter/soil and tree emissions were also quantified with chamber experiments. A zero-dimensional box model of HCHO mass balance in the canopy largely underestimated (×6) the vertical flux, attributable to either higher direct emissions than predicted by chamber measurements and/or missing VOCs with solar-driven emission profiles (unlike most terpenes). Satellite measurements of RGF, or the ratio of HCHO with glyoxal (another common OVOC), are used by global models to estimate the VOC mixture in certain areas. Measurements of RGF during both BEARPEX 2009 and BEACHON-ROCS 2010 showed increases due to biomass burning and fresh/strong anthropogenic influence while showing no change for old/weak anthropogenic influence. The RGF trend from urban to rural environments based on ground measurements was opposite of that observed by satellites. A solution to this discrepancy is vital to improving global models. 
Health and environmental sciences; Earth sciences; Atmospheric oxidation; Formaldehyde; Volatile organic compounds; Atmospheric Chemistry; Environmental science; 0371:Atmospheric Chemistry; 0768:Environmental science