Isoprene emissions and impacts over an ecological transition region in the US Upper Midwest inferred from tall tower measurements
Isoprene emissions and impacts over an ecological transition region in the US Upper Midwest inferred from tall tower measurements
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DOI：
10.1002/2014jd022732
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发表时间：
2015-04-27
影响因子：
4.4
通讯作者：
Hueber, Jacques
中科院分区：
文献类型：
--
作者：
Hu, Lu;Millet, Dylan B.;Hueber, Jacques
我们提出了1年的原位质子转移反应质谱仪（PTR-MS）测量异戊二烯及其氧化产物甲基乙烯基酮（MVK）和甲基丙烯醛（MACR）从一个244米高的塔在美国上中西部，位于之间的生态过渡异戊二烯排放的落叶林和主要是非异戊二烯排放的农业景观。我们发现，人为干扰（或人为异戊二烯）的平均22%的PTR-MS m/z 69信号在夏季白天，而MVK+MACR干扰（m/z 71）是次要的（7%）。在去除这些干扰后，观察到的异戊二烯和MVK+MACR丰度显示出明显的季节性周期，达到夏季最大值>2500 pptv（1小时平均值）。高塔受到附近和更远的区域异戊二烯源的影响，白天在西南风下异戊二烯增强（但MVK+MACR很少），其他时间MVK+MACR增强（但异戊二烯很少）。我们发现，GEOS-Chem大气模型与MEGANv2.1（天然气和气溶胶排放模型2.1版）生物源清单可以重现异戊二烯观测到模型的不确定性，改善土地覆盖和温度估计。然而，MVK+MACR中60%的低模型偏差无法解决，即使在NOx排放、化学、大气混合、干沉降、土地覆盖和潜在测量干扰的不同模型假设中也是如此。这意味着，虽然高塔附近的异戊二烯排放量被充分捕获，但在更广泛的区域内，它们被低估了。我们发现，该地区经历了一个强烈的季节性变化之间的VOC限制化学在春季和秋季和NOx限制或过渡化学在夏季，异戊二烯排放的时空分布的驱动。异戊二烯在引起这些化学位移中的作用可能被低估，因为对它的区域排放量的预测不足。
We present 1year of in situ proton transfer reaction mass spectrometer (PTR-MS) measurements of isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) from a 244m tall tower in the U.S. Upper Midwest, located at an ecological transition between isoprene-emitting deciduous forest and predominantly non-isoprene-emitting agricultural landscapes. We find that anthropogenic interferences (or anthropogenic isoprene) contribute on average 22% of the PTR-MS m/z 69 signal during summer daytime, whereas MVK+MACR interferences (m/z 71) are minor (7%). After removing these interferences, the observed isoprene and MVK+MACR abundances show pronounced seasonal cycles, reaching summertime maxima of >2500 pptv (1h mean). The tall tower is impacted both by nearby and more distant regional isoprene sources, with daytime enhancements of isoprene (but little MVK+MACR) under southwest winds and enhancements of MVK+MACR (but little isoprene) at other times. We find that the GEOS-Chem atmospheric model with the MEGANv2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) biogenic inventory can reproduce the isoprene observations to within model uncertainty given improved land cover and temperature estimates. However, a 60% low model bias in MVK+MACR cannot be resolved, even across diverse model assumptions for NOx emissions, chemistry, atmospheric mixing, dry deposition, land cover, and potential measurement interferences. This implies that, while isoprene emissions in the immediate vicinity of the tall tower are adequately captured, they are underestimated across the broader region. We show that this region experiences a strong seasonal shift between VOC-limited chemistry during the spring and fall and NOx-limited or transitional chemistry during the summer, driven by the spatiotemporal distribution of isoprene emissions. Isoprene's role in causing these chemical shifts is likely underestimated due to the underprediction of its regional emissions.