Dynamic light absorption of biomass-burning organic carbon photochemically aged under natural sunlight
Dynamic light absorption of biomass-burning organic carbon photochemically aged under natural sunlight
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DOI：
10.5194/acp-14-1517-2014
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发表时间：
2013-08
影响因子：
6.3
通讯作者：
M. Zhong;M. Jang
中科院分区：
文献类型：
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作者：
M. Zhong;M. Jang
抽象的。使用 104 m3 双室外室在自然阳光下，在阴燃条件下产生的木材燃烧气溶胶在不同的相对湿度 (RH) 和 NOx 条件下进行光化学老化。使用连接到积分球的紫外可见分光光度计测量光氧化过程中有机碳（OC）的光吸收。在高相对湿度下，颜色迅速衰减。氮氧化物稍微延长了木材烟雾的颜色，表明氮氧化物通过二次过程促进发色团的形成。总体而言，OC的质量吸收截面（在280和600 nm之间积分）在上午增加了11-54%（高RH除外），然后在下午逐渐减少19-68%。燃木有机碳光吸收的这种动态变化可以通过两种机制来解释：发色团形成和阳光漂白。为了研究化学转化对光吸收的影响，使用各种光谱仪对木材烟雾颗粒进行了表征。荧光强度主要与多环芳烃（PAHs）有关，随着时间的推移，荧光强度迅速下降，表明PAHs具有潜在的漂白作用。左旋葡聚糖浓度的下降表明初级有机气溶胶随时间的变化。通过傅里叶变换红外光谱测量的气溶胶含水量表明，随着光氧化的进行，木材燃烧气溶胶的吸湿性降低。在源自 2012 年佛罗里达州县线野火的环境烟雾气溶胶中也观察到了类似的光吸收变化趋势。我们得出的结论是，与新鲜木材燃烧的有机碳相比，在阳光照射 8-9 小时后，生物质燃烧的有机碳吸收的光变得更少。
Abstract. Wood-burning aerosol produced under smoldering conditions was photochemically aged with different relative humidity (RH) and NOx conditions using a 104 m3 dual outdoor chamber under natural sunlight. Light absorption of organic carbon (OC) was measured over the course of photooxidation using a UV–visible spectrometer connected to an integrating sphere. At high RH, the color decayed rapidly. NOx slightly prolonged the color of wood smoke, suggesting that NOx promotes the formation of chromophores via secondary processes. Overall, the mass absorption cross section (integrated between 280 and 600 nm) of OC increased by 11–54% (except high RH) in the morning and then gradually decreased by 19–68% in the afternoon. This dynamic change in light absorption of wood-burning OC can be explained by two mechanisms: chromophore formation and sunlight bleaching. To investigate the effect of chemical transformation on light absorption, wood smoke particles were characterized using various spectrometers. The intensity of fluorescence, which is mainly related to polycyclic aromatic hydrocarbons (PAHs), rapidly decreased with time, indicating the potential bleaching of PAHs. A decline of levoglucosan concentrations evinced the change of primary organic aerosol with time. The aerosol water content measured by Fourier transform infrared spectroscopy showed that wood-burning aerosol became less hygroscopic as photooxidation proceeded. A similar trend in light absorption changes has been observed in ambient smoke aerosol originating from the 2012 County Line wildfire in Florida. We conclude that the biomass-burning OC becomes less light absorbing after 8–9 h sunlight exposure compared to fresh wood-burning OC.