Observations of APAN during TexAQS 2000

Measurements of peroxycarboxylic nitric anhydrides (PANs) made in Houston, Texas during TexAQS (Texas Air Quality Study) 2000 showed a relatively abundant PAN compound that had not been identified in previous studies in North America [cf. Williams et al., 2000]. This compound was hypothesized to be peroxyacrylic nitric anhydride { CH2=CHC(O)OONO2, APAN} based on the work of Tanimoto and Akimoto, [2001]. APAN was synthesized and characterized on one of the two GC systems used to make those measurements, subsequent to the TexAQS 2000 field study, confirming that APAN was observed during TexAQS 2000, both on the ground and in airborne measurements. Mixing ratios of APAN were estimated from the response of the system to PAN and PPN and ranged up to 502 pptv, which was 30% of PAN. High APAN values were associated with the precursor species 1,3-butadiene and acrolein, which had local petrochemical sources. The presence of APAN at these unprecedented levels demonstrates the impact of these reactive VOC species, and may have associated health effects

Biomass burning and anthropogenic sources of CO over New England in the summer 2004

During the summer of 2004 large wildfires were burning in Alaska and Canada, and part of the emissions were transported toward the northeast United States, where they were measured during the NEAQS-ITCT 2k4 (New England Air Quality Study-Intercontinental Transport and Chemical Transformation) study on board the NOAA WP-3 aircraft and the NOAA research vessel Ronald H. Brown. Using acetonitrile and chloroform as tracers the biomass burning and the anthropogenic fraction of the carbon monoxide (CO) enhancement are determined. As much as 30% of the measured enhancement is attributed to the forest fires in Alaska and Canada transported into the region, and 70% is attributed to the urban emissions of mainly New York and Boston. On some days the forest fire emissions were mixed down to the surface and dominated the CO enhancement. The results compare well with the FLEXPART transport model, indicating that the total emissions during the measurement campaign for biomass burning might be about 22 Tg. The total U.S. anthropogenic CO sources used in FLEXPART are 25 Tg. FLEXPART model, using the U.S. EPA NEI-99 data, overpredicts the CO mixing ratio around Boston and New York in 2004 by about 50%. Copyright 2006 by the American Geophysical Union

Particle growth in urban and industrial plumes in Texas

Particle size distributions and gas-phase particle precursors and tracer species were measured aboard an aircraft in the plumes downwind from industrial and urban sources in the vicinity of Houston, TX during the daytime in late August and early September 2000. Plumes originating from the Parish gas-fired and coal-fired power plant, petrochemical industries along the Houston ship channel, the petrochemical facilities near the Gulf coast, and the urban center of Houston were studied. Most of the particle mass flux advected downwind of Houston came from the industries and electrical utilities at the periphery of the city rather than from sources in the urban core. In SO2-rich plumes that did not contain elevated concentrations of volatile organic compounds (VOCs), particle volume increased with increasing plume oxidation (age) at a rate consistent with condensation and neutralization of the gas-phase oxidation products Of SO2. In plumes that were rich in both SO2 and VOCs, observed particle growth greatly exceeded that expected from SO2 oxidation, indicating the formation of organic particulate mass. In plumes that were enhanced in VOCs but not in SO2, and in the plume of the Houston urban center, no particle volume growth with increasing plume oxidation was detected. Since substantial particle volume growth was associated only with SO2-rich plumes, these results suggest that photochemical oxidation of SO2 is the key process regulating particle mass growth in all the studied plumes in this region. However, uptake of organic matter probably contributes substantially to particle mass in petrochemical plumes rich in both SO2 and VOCs. Quantitative studies of particle formation and growth in photochemical systems containing nitrogen oxides (NOx = NO + NO2 ), VOCs, and SO2 are recommended to extend those previously made in NOx-VOC systems

Multiscale simulations of tropospheric chemistry in the eastern Pacific and on the U.S. West Coast during spring 2002

Regional modeling analysis for the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) experiment over the eastern Pacific and U.S. West Coast is performed using a multiscale modeling system, including the regional tracer model Chemical Weather Forecasting System (CFORS), the Sulfur Transport and Emissions Model 2003 (STEM-2K3) regional chemical transport model, and an off-line coupling with the Model of Ozone and Related Chemical Tracers (MOZART) global chemical transport model. CO regional tracers calculated online in the CFORS model are used to identify aircraft measurement periods with Asian influences. Asian-influenced air masses measured by the National Oceanic and Atmospheric Administration (NOAA) WP-3 aircraft in this experiment are found to have lower ΔAcetone/ΔCO, ΔMethanol /ΔCO, and ΔPropane/ ΔEthyne ratios than air masses influenced by U.S. emissions, reflecting differences in regional emission signals. The Asian air masses in the eastern Pacific are found to usually be well aged (\u3e5 days), to be highly diffused, and to have low NOy levels. Chemical budget analysis is performed for two flights, and the O3 net chemical budgets are found to be negative (net destructive) in the places dominated by Asian influences or clear sites and positive in polluted American air masses. During the trans-Pacific transport, part of gaseous HNO3 was converted to nitrate particle, and this conversion was attributed to NOy decline. Without the aerosol consideration, the model tends to overestimate HNO3 background concentration along the coast region. At the measurement site of Trinidad Head, northern California, high- concentration pollutants are usually associated with calm wind scenarios, implying that the accumulation of local pollutants leads to the high concentration. Seasonal variations are also discussed from April to May for this site. A high-resolution nesting simulation with 12-km horizontal resolution is used to study the WP-3 flight over Los Angeles and surrounding areas. This nested simulation significantly improved the predictions for emitted and secondary generated species. The difference of photochemical behavior between the coarse (60-km) and nesting simulations is discussed and compared with the observation. Copyright 2004 by the American Geophysical Union

Trace gas emissions through a winter snowpack in the subalpine ecosystem at Niwot Ridge, Colorado

A preliminary study of whole air measurements within a snowpack in the subalpine forest of Colorado found that lower snow layers and underlying soil were a strong source of chemically active trace gases (VOC). The emissions of trace gases were correlated with emissions of radiatively active greenhouse gases (CO2 and N2O) through the snowpack. Carbon dioxide was enhanced in the lower snowpack to over 1000 ppmv, similar to previous studies, which have shown that a thermal insulation of snow covering the soil leads to enhanced emissions of CO2 equivalent to a large fraction of annual respiration. Comparable enhancements of several VOCs reached 1275, 1670, and 1000 pptv for methyl chloride, propane, and α‐pinene, respectively. The measurements are limited to a one‐day pilot study, however, considering that previous studies have reported significant CO2 emissions through snowpacks any emissions of VOC may also be important on a local or potentially global scale

Evidence from firn air for recent decreases in non-methane hydrocarbons and a 20th century increase in nitrogen oxides in the northern hemisphere

The atmospheric evolution of eight non-methane hydrocarbons (ethane, acetylene, propane, n-butane, isobutane, n-pentane, isopentane and benzene) and five alkyl nitrates (2-propyl, 2-butyl, 3-methyl-2-butyl and the sum of 2+3-pentyl nitrates) are reconstructed for the latter half of the 20th century based on Arctic firn air measurements. The reconstructed trends of the non-methane hydrocarbons (NMHCs) show increasing concentrations from 1950 to a maximum in 1980 before declining towards the end of last century. These observations provide direct evidence that NMHCs in the northern hemisphere have declined substantially during the period 1980–2001. Benzene concentrations show a smaller increase between 1950 and 1980 than the other NMHCs indicating that additional sources of benzene, other than fossil fuel combustion, were likely important contributors to the benzene budget prior to and during this period. The declining benzene concentrations from 1980 to 2001 would suggest that biomass burning is unlikely to be important in the benzene budget as biomass burning emissions were reportedly increasing over the same period. Methyl and ethyl nitrate show growth patterns in the firn that suggested perturbation by in-situ production from an unidentified mechanism. However, the higher alkyl nitrates show evidence for increasing concentrations from 1950 to maxima in the mid 1990s before decreasing slightly toward the end of the last century. The differing atmospheric evolution of the alkyl nitrates relative to their parent hydrocarbons indicate an increase in their production efficiency per hydrocarbon molecule. Using a steady state analysis of hydrocarbon oxidation and alkyl nitrate production and loss we show that reactive nitrogen oxide (NOx) concentrations in the northern hemisphere have likely increased considerably between 1950 and 2001. ► NMHC abundances increased from 1950 to 1980 followed by notable declines. ► Alkyl nitrate abundances increased from 1950 to mid 1990s followed by small declines. ► Overall increase in alkyl nitrates greater than NHMCs indicating importance of additional factor, i.e., NOx. ► Alkyl nitrate to hydrocarbon relationships showed evidence for 20th century increase in NOx

Multiscale simulations of tropospheric chemistry in the eastern Pacific and on the U.S. West Coast during spring 2002

Regional modeling analysis for the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) experiment over the eastern Pacific and U.S. West Coast is performed using a multiscale modeling system, including the regional tracer model Chemical Weather Forecasting System (CFORS), the Sulfur Transport and Emissions Model 2003 (STEM-2K3) regional chemical transport model, and an off-line coupling with the Model of Ozone and Related Chemical Tracers (MOZART) global chemical transport model. CO regional tracers calculated online in the CFORS model are used to identify aircraft measurement periods with Asian influences. Asian-influenced air masses measured by the National Oceanic and Atmospheric Administration (NOAA) WP-3 aircraft in this experiment are found to have lower ΔAcetone/ΔCO, ΔMethanol /ΔCO, and ΔPropane/ ΔEthyne ratios than air masses influenced by U.S. emissions, reflecting differences in regional emission signals. The Asian air masses in the eastern Pacific are found to usually be well aged (\u3e5 days), to be highly diffused, and to have low NOy levels. Chemical budget analysis is performed for two flights, and the O3 net chemical budgets are found to be negative (net destructive) in the places dominated by Asian influences or clear sites and positive in polluted American air masses. During the trans-Pacific transport, part of gaseous HNO3 was converted to nitrate particle, and this conversion was attributed to NOy decline. Without the aerosol consideration, the model tends to overestimate HNO3 background concentration along the coast region. At the measurement site of Trinidad Head, northern California, high- concentration pollutants are usually associated with calm wind scenarios, implying that the accumulation of local pollutants leads to the high concentration. Seasonal variations are also discussed from April to May for this site. A high-resolution nesting simulation with 12-km horizontal resolution is used to study the WP-3 flight over Los Angeles and surrounding areas. This nested simulation significantly improved the predictions for emitted and secondary generated species. The difference of photochemical behavior between the coarse (60-km) and nesting simulations is discussed and compared with the observation. Copyright 2004 by the American Geophysical Union