Browsing by Author "Gong, L."
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Item Airmass aging metrics derived from particle and other measurements near Fort Worth(Elsevier, 2016) Cevik, B. Karakurt; Rutter, A.P.; Gong, L.; Griffin, R.J.; Flynn, J.H.; Lefer, B.L.; Kim, S.The composition, concentration, and size of submicron particulate matter (PM1) were measured at five-minute resolution by an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at a semi-rural location northwest of the Dallas-Fort Worth, TX, area during June 2011. Because of increased organic aerosol (OA) levels, focus here is placed on the period from June 17–30. The total measured PM1 mass concentration ranged between 1.1 and 16.5 μg m−3, with a mean of 4.4 ± 2.6 (one s.d.) μg m−3. Significant variability is observed in the time series of total PM1 and of four individual HR-ToF-AMS species, particularly between June 21 and 25. The average PM1mass composition was dominated by OA (55.0 ± 14.8%) and sulfate (30.7 ± 12.3%). Organic aerosol concentrations were correlated positively with carbon monoxide (CO) (R = 0.81). This study uses a variety of aging metrics and their relations to OA/ΔCO to characterize secondary organic aerosol. Photochemical age is estimated by using the toluene to benzene ratio. The average photochemical age was 26.7 ± 5.3 h. Other metrics of age used in this work include the ratio of sulfate to total sulfur and the ratio of nitrogen oxides to total reactive nitrogen. The correlations between the OA/ΔCO and nitrogen aging metrics indicate consistent aging, and a weak relationship is observed between OA/ΔCO and sulfur aging. However, the relationship between photochemical age and OA/ΔCO does not show a statistically significant correlation.Item Impact of Environmental Variables on the Reduction of Nitric Acid by Proxies for Volatile Organic Compounds Emitted by Motor Vehicles(Elsevier, 2016) Leong, Y.J.; Rutter, A.P.; Wong, H.Y.; Gutierrez, C.V.; Junaid, M.; Scheuer, E.; Gong, L.; Lewicki, R.; Dibb, J.E.; Tittel, F.K.; Griffin, R.J.Recent work has identified nitric acid (HNO3) as a potential precursor of nitrous acid (HONO), which is an important source of oxidants that regulate ozone and particulate pollution. Recent work in our laboratory has indicated that the reduction of HNO3 to HONO can occur homogeneously in the presence of surrogates for volatile organic compounds (VOCs) emitted by motor vehicles. This study focuses on the impact of environmental variables on the rate of formation of HONO in this process. The observed base case (25.0 °C and ∼20.0% relative humidity (RH)) HONO formation rate was 0.54 ± 0.09 ppb h−1, values comparable to enhancements observed in HONO during morning rush hour in Houston, TX. The rate was enhanced at lower temperatures of ∼20.0 °C, but the rate remained statistically similar (1σ) for experiments conducted at temperatures of 25 °C, 30 °C, and 35 °C. The assumption that multiple reactive components of the VOC mixture react with HNO3 is supported by this observation, and the relative importance of each reactive species in the reaction may vary with temperature. The enhanced rate at lower temperatures could make the proposed reaction mechanism more important at night. The formation rate of HONO does not change substantially when initial HNO3 concentration is varied between 400 and 4600 ppt, suggesting that the concentration of reactive VOCs was the limiting factor. The reduction of HNO3 to HONO appears not to occur heterogeneously on the aerosol surfaces tested. The presence of ∼120 ppb of ammonia has no observable impact on the reaction. However, it is likely that UV irradiation (λ = 350 nm) decreases the formation rate of HONO either by consuming the reactive VOCs involved or by directly interfering with the reaction. The “renoxification” of less reactive HNO3 to more reactive HONO has significant implications for daytime ozone and particulate pollution.