Seasonal variation of levoglucosan in aerosols over the western North Pacific and its assessment as a biomass-burning tracer
Seasonal variation of levoglucosan in aerosols over the western North Pacific and its assessment as a biomass-burning tracer
复制标题
DOI：
10.1016/j.atmosenv.2010.06.017
复制
发表时间：
2010-09
影响因子：
5
通讯作者：
M. Mochida;K. Kawamura;P. Fu;T. Takemura
中科院分区：
文献类型：
--
作者：
M. Mochida;K. Kawamura;P. Fu;T. Takemura
左旋葡聚糖被认为是大气中生物质燃烧气溶胶的有效分子示踪剂。为了表征其浓度在太平洋的季节性变化，并评估其作为示踪剂后，远程传输的有用性，我们调查了左旋葡聚糖在秩智岛在北太平洋西部的长期变化，从2001年至2004年。分析有机碳（OC）、元素碳（EC）和d-葡萄糖以进行比较。左旋葡聚糖浓度的季节变化表现出最大值在冬季，这是一致的增强亚洲外流到太平洋的落后的空气质量轨迹。从全球气溶胶模型输出估计的左旋葡聚糖在冬季的浓度水平，平均而言，与观察到的水平，这表明有相当一部分的左旋葡聚糖没有分解，从亚洲大陆的西风/西北风的远程传输。这一结果是支持的左旋葡聚糖EC在秩次岛和东亚沿海地区的可比比例。相反，在夏季测得的左旋葡聚糖的浓度显着低于建模。这意味着在太平洋上空停滞的气团中左旋葡聚糖的降解，尽管模型估计的不确定性也可能是造成这种差异的部分原因。一种可能的降解途径是OH自由基氧化;酸催化反应的贡献需要进一步研究。
Levoglucosan is considered as a useful molecular tracer of biomass-burning aerosols in the atmosphere. To characterize the seasonal variation of its concentrations over the Pacific Ocean and to assess its usefulness as a tracer after long-range transport, we investigated long-term variations of levoglucosan over Chichi-jima in the western North Pacific, from 2001 to 2004. Organic carbon (OC), elemental carbon (EC) and d-glucose were analyzed for comparison. The seasonal variation of levoglucosan concentrations showed a maximum in the winter, which is consistent with the enhanced Asian outflow to the Pacific indicated by backward air-mass trajectories. The concentration levels of levoglucosan estimated from global aerosol model outputs in the winter are, on average, comparable to the observed levels, suggesting that a considerable fraction of levoglucosan did not decompose during long-range transport from the Asian continent by westerly/northwesterly winds. This result is supported by comparable ratios of levoglucosan to EC in Chichi-jima and the East Asian coastal region. Conversely, the measured concentrations of levoglucosan in the summer were significantly lower than the modeled one. This implies a degradation of levoglucosan in the air masses that stagnated over the Pacific, although uncertainties in the model estimate may also be partly responsible for this discrepancy. One possible degradation pathway is oxidation by OH radicals; the contribution of acid-catalyzed reactions needs further investigation.