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Soil and leaf litter are significant global sources of small oxidized volatile organic compounds, VOCs (e.g., methanol and acetaldehyde). They may also be significant sources of larger VOCs that could act as precursors to secondary organic aerosol (SOA) formation. To investigate this, soil and leaf litter samples were collected from the University of Idaho Experimental Forest and transported to the laboratory. There, the VOC emissions were characterized and used to drive SOA formation via dark, ozone-initiated reactions. Monoterpenes dominated the emission profile with emission rates as high as 228 μg-C m(-2) h(-1). The composition of the SOA produced was similar to biogenic SOA formed from oxidation of ponderosa pine emissions and α-pinene. Measured soil and litter monoterpene emission rates were compared with modeled canopy emissions. Results suggest surface soil and litter monoterpene emissions could range from 12 to 136% of canopy emissions in spring and fall. Thus, emissions from leaf litter may potentially extend the biogenic emissions season, contributing to significant organic aerosol formation in the spring and fall when reduced solar radiation and temperatures reduce emissions from living vegetation.

The objective was to determine the efficacy of a vermifiltration system that treats liquid cattle manure to alter methane (CH4), nitrous oxide (N2O), ammonia (NH3) emissions, and nutrient composition (potassium-K; phosphorus-P; nitrogen-N). Liquid manure was sampled as it entered the worm-bed (influent) and as it exited from the worm-bed (effluent) to measure changes in nutrient composition. Worm-bed surface fluxes of CH4 and N2O were measured in real-time for three distinct environmental temperatures (0 ËšC, 10 ËšC, and 20 ËšC) to examine seasonal variation at several locations in the 3.64 ha worm-bed using isolation chambers and cavity ringdown spectrometry. NH3 flux was measured from the chambers using a ChemComb 3500 Speciation Collection Cartridge and coated honeycomb denuders. NH3 samples were eluted within 4 h of collection and stored at -20 ËšC until colorimetric analysis. Duplicate NH3 measurements were made for each chamber location at each temperature. Examination of the influx and efflux data indicates reductions of 25% in K, 96% in P, 99% in total suspended solids, 92% in volatile solids, and 92% in total Kjeldahl N. Chamber CH4 concentrations at 0 ËšC (0.51 to 1.18 ppm) tended to be less at 10 ËšC (2.17 to 2.67 ppm) and 20 ËšC (1.6 to 2.45 ppm) but were not different across temperatures (P < .077) and reflected ambient concentrations (2.44 ppm). N2O concentrations at 0 ËšC (157.00 to 224.00 ppb) and 10 ËšC (86.3 to 176.5 ppb) were not different than ambient (358.5 ppb), but at 20 ËšC (400.0 to 655.0 ppb) concentrations tended to be greater (P < 0.07). NH3 concentrations at 0 ËšC (0.06 to 0.33 ppm) and 20 ËšC (1.35 and 2.21 ppm) were not different but at 10 ËšC (11.8 to 28.7 ppm) were greater (P < 0.05). Fluxes were calculated for each sampling period. During 0 ËšC flux densities were 1.61 ± 0.17 mg· m-2· day-1 for N2O, 2.5 0.57mg m-2· day-1 for CH4, and 0.007± 0.00 mg m-2· day-1 for NH3. At 20ËšC flux densities were 1.98± 0.63 mg· m-2day-1 for N2O, 2.88± 0.755 mg m-2· day-1 for CH4, and 25.4 ± 0.0 mg· m-2· day-1 for NH3. Flux calculations and extrapolation of emission rates to the entire system indicates that vermifiltration is an effective strategy to alter nutrient concentrations and reduce CH4 emissions but not emissions of N2O and NH3. [ABSTRACT FROM AUTHOR]

Gas-phase biogenic volatile organic compounds (BVOCs) are oxidized in the troposphere to produce secondary pollutants such as ozone (O3), organic nitrates (RONO2), and secondary organic aerosol (SOA). The nitrate radical (NO3) is especially reactive towards isoprene and monoterpenes such as α-pinene. A zero-dimensional model has been used to investigate differences in oxidation and SOA production from these two BVOCs, especially with respect to hydroxyl radical (OH) and NO3, above and below a forest canopy in rural Michigan using local data and data from a monitoring site in Detroit. In all modeled scenarios, NO3 concentrations are relatively small (0.5-3 pptv); however, daytime concentrations below the canopy are two-to-three times larger than those above. In the rural scenario, NO3 contributes up to 20% of daytime oxidation of α-pinene below the canopy, and this contribution increases to around 40% in the polluted cases. Oxidation of isoprene is almost entirely dominated by reaction with OH, as expected. The most significant first-generation RONO2 formation mechanism varies significantly between scenarios and by canopy location. Nonetheless, in every scenario, daytime production of first-generation RONO2 through NO3 + α-pinene is more significant below the canopy than above. While SOA mass loadings are moderate (2 μg m-3 or less), total SOA production is consistently enhanced below the canopy, due to the combined effects of elevated isoprene and reduced NO concentrations. Furthermore, below the canopy, the total amount of RONO2 SOA produced through NO3 oxidation of α-pinene during the daytime (10:00-18:00), while small in absolute terms, is more than twice as large as the amount produced above the canopy during that time period in every scenario. In the rural ambient case, a minimum of 74% of α-pinene RONO2 SOA is formed solely from initial oxidation by NO3. The relative abundances of HO2 and NO are shown to substantially impact both total SOA production and RONO2 SOA composition. The results presented emphasize the need for more detailed studies regarding the influence of NO3 throughout forest canopies in different environments. [ABSTRACT FROM AUTHOR]