The size and frequency of wildfires in the western United States have been increasing, and this trend is projected to continue, with increasing adverse consequences for human health. Gas- and particle-phase organic compounds are the main components of wildfire emissions. Some of the directly emitted compounds are hazardous air pollutants, while others can react with oxidants to form secondary air pollutants such as ozone and secondary organic aerosol (SOA). Further, compounds emitted in the particle phase can volatize during smoke transport and can then serve as precursors for SOA. The extent of pollutant formation from wildfire emissions is dependent in part on the speciation of organic compounds. The most detailed speciation of organic compounds has been achieved in laboratory studies, though recent field campaigns are leading to an increase in such measurements in the field. In this study, we identified and quantified hundreds of gas- and particle-phase organic compounds emitted from conifer-dominated wildfires in the western US, using two two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC ToF-MS) instruments. Observed emission factors (EFs) and emission ratios are reported for four wildfires. As has been demonstrated previously, modified combustion efficiency (MCE) was a good predictor of particle-phase EFs (e.g., R²=0.78 and 0.84 for sugars and terpenoids, respectively), except for elemental carbon. Higher emissions of diterpenoids, resin acids, and monoterpenes were observed in the field relative to laboratory studies, likely due to distillation from unburned heated vegetation, which may be underrepresented in laboratory studies. These diterpenoids and resin acids accounted for up to 45 % of total quantified organic aerosol, higher than the contribution from sugar and sugar derivatives. The low volatility of resin acids makes them ideal markers for conifer fire smoke. The speciated measurements also show that evaporation of semi-volatile organic compounds took place in smoke plumes, which suggests that the evaporated primary organic aerosol can be a precursor of SOAs in wildfire smoke plumes.

中文翻译：

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美国西部野火的有机化合物排放及其近火转化

美国西部野火的规模和频率一直在增加，预计这一趋势将持续下去，对人类健康造成的不利后果越来越多。气相和颗粒相有机化合物是野火排放的主要成分。一些直接排放的化合物是有害的空气污染物，而另一些可以与氧化剂反应形成二次空气污染物，如臭氧和二次有机气溶胶（SOA）。此外，在颗粒相中排放的化合物可以在烟雾传输过程中挥发，然后可以作为 SOA 的前体。野火排放物形成污染物的程度部分取决于有机化合物的形态。最详细的有机化合物形态已在实验室研究中实现，尽管最近的实地活动导致实地此类测量的增加。在这项研究中，我们使用二维气相色谱结合飞行时间质谱（GC ×  GC ToF-MS) 仪器。报告了四场野火的观测排放因子 (EF) 和排放比率。如前所述，改进的燃烧效率 (MCE) 是颗粒相 EF 的良好预测指标（例如，R ² =0糖和萜类化合物分别为 0.78 和 0.84），但元素碳除外。相对于实验室研究，在现场观察到更高的二萜类、树脂酸和单萜排放，这可能是由于未燃烧的加热植被的蒸馏，这可能在实验室研究中代表性不足。这些二萜和树脂酸占总量化有机气溶胶的 45%，高于糖和糖衍生物的贡献。树脂酸的低挥发性使其成为针叶树火灾烟雾的理想标记。特定的测量还表明，半挥发性有机化合物的蒸发发生在烟羽中，这表明蒸发的初级有机气溶胶可能是野火烟羽中 SOA 的前体。