School of Science and Technology, University of Washington-Bothell , Bothell, Washington 98011, United States.
Environ Sci Technol. 2013 Oct 1;47(19):11065-72. doi: 10.1021/es402164f. Epub 2013 Sep 13.
Wildfires generate substantial emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). As such, wildfires contribute to elevated ozone (O3) in the atmosphere. However, there is a large amount of variability in the emissions of O3 precursors and the amount of O3 produced between fires. There is also significant interannual variability as seen in median O3, organic carbon and satellite derived carbon monoxide mixing ratios in the western U.S. To better understand O3 produced from wildfires, we developed a statistical model that estimates the maximum daily 8 h average (MDA8) O3 as a function of several meteorological and temporal variables for three urban areas in the western U.S.: Salt Lake City, UT; Boise, ID; and Reno, NV. The model is developed using data from June-September 2000-2012. For these three locations, the statistical model can explain 60, 52, and 27% of the variability in daily MDA8. The Statistical Model Residual (SMR) can give information on additional sources of O3 that are not explained by the usual meteorological pattern. Several possible O3 sources can explain high SMR values on any given day. We examine several cases with high SMR that are due to wildfire influence. The first case considered is for Reno in June 2008 when the MDA8 reached 82 ppbv. The wildfire influence for this episode is supported by PM concentrations, the known location of wildfires at the time and simulations with the Weather and Research Forecasting Model with Chemistry (WRF-Chem) which indicates transport to Reno from large fires burning in California. The contribution to the MDA8 in Reno from the California wildfires is estimated to be 26 ppbv, based on the SMR, and 60 ppbv, based on WRF-Chem. The WRF-Chem model also indicates an important role for peroxyacetyl nitrate (PAN) in producing O3 during transport from the California wildfires. We hypothesize that enhancements in PAN due to wildfire emissions may lead to regional enhancements in O3 during high fire years. The second case is for the Salt Lake City (SLC) region for August 2012. During this period the MDA8 reached 83 ppbv and the SMR suggests a wildfire contribution of 19 ppbv to the MDA8. The wildfire influence is supported by PM2.5 data, the known location of wildfires at the time, HYSPLIT dispersion modeling that indicates transport from fires in Idaho, and results from the CMAQ model that confirm the fire impacts. Concentrations of PM2.5 and O3 are enhanced during this period, but overall there is a poor relationship between them, which is consistent with the complexities in the secondary production of O3. A third case looks at high MDA8 in Boise, ID, during July 2012 and reaches similar conclusions. These results support the use of statistical modeling as a tool to quantify the influence from wildfires on urban O3 concentrations.
野火会产生大量的氮氧化物 (NOx) 和挥发性有机化合物 (VOCs)。因此，野火会导致大气中臭氧 (O3) 浓度升高。然而，火灾之间 O3 前体的排放和产生的 O3 量存在很大的可变性。在美国西部，臭氧、有机碳和卫星衍生一氧化碳混合比的中值也存在显著的年际变化。为了更好地了解野火产生的 O3，我们开发了一个统计模型，该模型可以根据美国西部三个城市（犹他州盐湖城、爱达荷州博伊西和内华达州里诺）的几个气象和时间变量来估计最大日 8 小时平均 (MDA8) 的 O3。该模型是使用 2000 年至 2012 年 6 月至 9 月的数据开发的。对于这三个地点，统计模型可以解释每日 MDA8 变化的 60%、52%和 27%。统计模型残差 (SMR) 可以提供有关通常气象模式无法解释的 O3 其他来源的信息。在任何给定的日子里，有几个可能的 O3 来源可以解释较高的 SMR 值。我们检查了几个由于野火影响而导致 SMR 值较高的情况。第一个案例是 2008 年 6 月里诺的情况，当时 MDA8 达到了 82ppbv。该事件的野火影响得到了 PM 浓度、当时已知的野火位置以及天气和研究预报模型与化学模型（WRF-Chem）模拟的支持，这些模拟表明大火从加利福尼亚州燃烧到里诺。根据 SMR，估计加利福尼亚州野火对里诺 MDA8 的贡献为 26ppbv，根据 WRF-Chem 为 60ppbv。WRF-Chem 模型还表明，过氧乙酰硝酸酯 (PAN) 在从加利福尼亚州野火运输过程中产生 O3 方面发挥了重要作用。我们假设由于野火排放而增强的 PAN 可能导致高火灾年份期间 O3 的区域增强。第二个案例是 2012 年 8 月盐湖城 (SLC) 地区的情况。在此期间，MDA8 达到 83ppbv，SMR 表明野火对 MDA8 的贡献为 19ppbv。PM2.5 数据、当时已知的野火位置、表明来自爱达荷州野火的 HYSPLIT 分散模型以及 CMAQ 模型的结果都支持野火的影响，这些结果证实了火灾的影响。在此期间，PM2.5 和 O3 的浓度都有所增加，但总体上它们之间的关系很差，这与 O3 的二次生成的复杂性一致。第三个案例研究了 2012 年 7 月 Boise，ID 期间的高 MDA8，并得出了类似的结论。这些结果支持使用统计模型作为量化野火对城市 O3 浓度影响的工具。
