Bibliography - A. M. Fiore

1. Naik, V., A. M. Fiore, L. W. Horowitz, and H. B. Singh, et al., 2010: Observational constraints on the global atmospheric budget of ethanol. Atomsphere Chemistry and Physics Discussion, http://www.atmos-chem-phys-discuss.net/10/925/2010/acpd-10-925-2010.pdf, 10, 925-945
   [ Abstract ]

   Energy security and climate change concerns have led to the promotion of biomass-derived ethanol, an oxygenated volatile organic compound (OVOC), as a substitute for fossil fuels. Although ethanol is ubiquitous in the troposphere, our knowledge of its current atmospheric budget and distribution is limited. Here, for the first time we use a global chemical transport model in conjunction with atmospheric observations to place constraints on the ethanol budget, noting that additional measurements of ethanol (and its precursors) are still needed to enhance confidence in our estimated budget. Global sources of ethanol in the model include 5.0 Tg yr⁻¹from industrial sources and biofuels, 9.2 Tg yr⁻¹ from terrestrial plants, ~0.5 Tg yr⁻¹ from biomass burning, and 0.05 Tg yr⁻¹ from atmospheric reactions of the ethyl peroxide radical (C₂H₅O₂) with itself and with the methyl peroxide radical (CH₃O₂). The resulting atmospheric lifetime of ethanol in the model is 2.8 days. Gas-phase oxidation by hydroxyl radical (OH) is the primary global sink of ethanol in the model (65%), followed by dry deposition to land (25%), and wet deposition (10%). Over continental areas, ethanol concentrations predominantly reflect direct anthropogenic and biogenic emission sources. Uncertainty in the biogenic ethanol emissions estimated at a factor of three may contribute to the 50% model underestimate of observations in the North American boundary layer. Furthermore, current levels of ethanol measured in remote atmospheres are an order of magnitude larger than those explained by surface sources or by in-situ atmospheric production from observed precursor hydrocarbons in the model, suggesting a major gap in understanding. Stronger constraints on the budget and distribution of ethanol and other VOCs are a critical step towards assessing the impacts of increasing use of ethanol as a fuel.

2. Fiore, A. M., L. W. Horowitz, D. W. Purves, H. Levy II, M. J. Evans, Y. Wang, Y. Li, and R. M. Yantosca, 2005: Evaluating the contribution of changes in isoprene emissions to surface ozone trends over the eastern United States. Journal of Geophysical Research, 110(D12303), doi:10.1029/2004JD005485
   [ Abstract ]

   Reducing surface ozone (O₃) to concentrations in compliance with the national air quality standard has proven to be challenging, despite tighter controls on O₃ precursor emissions over the past few decades. New evidence indicates that isoprene emissions changed considerably from the mid-1980s to the mid-1990s owing to land-use changes in the eastern United States (Purves et al., 2004). Over this period, U.S. anthropogenic VOC (AVOC) emissions decreased substantially. Here we apply two chemical transport models (GEOS-CHEM and MOZART-2) to test the hypothesis, put forth by Purves et al. (2004), that the absence of decreasing O₃ trends over much of the eastern United States may reflect a balance between increases in isoprene emissions and decreases in AVOC emissions. We find little evidence for this hypothesis; over most of the domain, mean July afternoon (1300–1700 local time) surface O₃ is more responsive (ranging from -9 to +7 ppbv) to the reported changes in anthropogenic NO_x emissions than to the concurrent isoprene (-2 to +2 ppbv) or AVOC (-2 to 0 ppbv) emission changes. The estimated magnitude of the O₃ response to anthropogenic NO_x emission changes, however, depends on the base isoprene emission inventory used in the model. The combined effect of the reported changes in eastern U.S. anthropogenic plus biogenic emissions is insufficient to explain observed changes in mean July afternoon surface O₃ concentrations, suggesting a possible role for decadal changes in meteorology, hemispheric background O₃, or subgrid-scale chemistry. We demonstrate that two major uncertainties, the base isoprene emission inventory and the fate of isoprene nitrates (which influence surface O₃ in the model by -15 to +4 and +4 to +12 ppbv, respectively), preclude a well-constrained quantification of the present-day contribution of biogenic or anthropogenic emissions to surface O₃ concentrations, particularly in the high-isopreneemitting southeastern United States. Better constraints on isoprene emissions and chemistry are needed to quantitatively address the role of isoprene in eastern U.S. air quality.

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