Undisturbed and disturbed above canopy ponderosa pine emissions: PTR-TOF-MS measurements and MEGAN 2.1 model results
Undisturbed and disturbed above canopy ponderosa pine emissions: PTR-TOF-MS measurements and MEGAN 2.1 model results
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DOI：
10.5194/acp-13-11935-2013
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发表时间：
2013-12
影响因子：
6.3
通讯作者：
L. Kaser;T. Karl;A. Guenther;M. Graus;R. Schnitzhofer;A. Turnipseed;L. Fischer;P. Harley;M. Madronich;D. Gochis;F. Keutsch;A. Hansel
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作者：
L. Kaser;T. Karl;A. Guenther;M. Graus;R. Schnitzhofer;A. Turnipseed;L. Fischer;P. Harley;M. Madronich;D. Gochis;F. Keutsch;A. Hansel
抽象的。我们首次使用质子转移反应飞行时间质谱仪 (PTR-TOF-MS) 在美国科罗拉多州的黄松林上空对挥发性有机化合物 (VOC) 进行涡流协方差通量测量。 PTR-TOF-MS 的高质量分辨率能够识别化学和式。在2010年8月和9月的30天测量期间，在环境空气质谱中检测到649个不同的离子质量峰（包括初级离子和质量校准化合物）。计算所有离子质量峰与垂直风速的涡流协方差。在典型的一天中，17 个离子质量峰，包括质子化母体化合物、其碎片和同位素以及 VOC-H + -水簇，显示出显着的通量，白天平均排放量高于 0.1 mg 化合物 m -2 h -1 的可靠通量阈值。这些离子质量峰可归属于七个化合物类别。白天（10:00–18:00 LT）的主要通量贡献归因于 2-甲基-3-丁烯-2-醇 (MBO) 和异戊二烯 (50%) 的总和、甲醇 (12%)、乙酸和乙醇醛 (10%) 的总和以及单萜 (10%) 的总和。总MBO+异戊二烯通量由10%异戊二烯和90%MBO组成。本工作中观察到的 MBO 和异戊二烯之和的光和温度依赖性与早期研究的结果非常一致。将上述 MBO 和异戊二烯总和以及单萜总和的冠层通量测量值与使用自然气体和气溶胶排放模型 (MEGAN 2.1) 计算的排放量进行了比较。 MEGAN 2.1 和测量结果之间的最佳一致性是通过使用根据特定地点的叶片比色皿测量确定的排放因子来实现的。虽然建模和测量的 MBO + 异戊二烯通量非常吻合，但 MEGAN 2.1 低估了单萜总量的排放量。这是预料之中的，因为 MEGAN 2.1 中未包含一些影响单萜排放的因素，例如风暴造成的针叶和树枝的物理损坏。在一场严重的冰雹事件之后，22 个离子质量峰（归因于六种化合物类别以及一些未知化合物）在接下来的两天内显示出通量升高。与冰雹之前的排放量相比，单萜排放总量增加了 4-23 倍，而 MBO 排放量保持不变。如果不考虑该干扰源的影响，则该测量期间的单萜排放量（以毫克化合物m -2 为单位）被低估40%。
Abstract. We present the first eddy covariance flux measurements of volatile organic compounds (VOCs) using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) above a ponderosa pine forest in Colorado, USA. The high mass resolution of the PTR-TOF-MS enabled the identification of chemical sum formulas. During a 30 day measurement period in August and September 2010, 649 different ion mass peaks were detected in the ambient air mass spectrum (including primary ions and mass calibration compounds). Eddy covariance with the vertical wind speed was calculated for all ion mass peaks. On a typical day, 17 ion mass peaks, including protonated parent compounds, their fragments and isotopes as well as VOC-H + -water clusters, showed a significant flux with daytime average emissions above a reliable flux threshold of 0.1 mg compound m −2 h −1 . These ion mass peaks could be assigned to seven compound classes. The main flux contributions during daytime (10:00–18:00 LT) are attributed to the sum of 2-methyl-3-buten-2-ol (MBO) and isoprene (50%), methanol (12%), the sum of acetic acid and glycolaldehyde (10%) and the sum of monoterpenes (10%). The total MBO + isoprene flux was composed of 10% isoprene and 90% MBO. There was good agreement between the light- and temperature dependency of the sum of MBO and isoprene observed for this work and those of earlier studies. The above canopy flux measurements of the sum of MBO and isoprene and the sum of monoterpenes were compared to emissions calculated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN 2.1). The best agreement between MEGAN 2.1 and measurements was reached using emission factors determined from site-specific leaf cuvette measurements. While the modeled and measured MBO + isoprene fluxes agree well, the emissions of the sum of monoterpenes is underestimated by MEGAN 2.1. This is expected as some factors impacting monoterpene emissions, such as physical damage of needles and branches due to storms, are not included in MEGAN 2.1. After a severe hailstorm event, 22 ion mass peaks (attributed to six compound classes plus some unknown compounds) showed an elevated flux for the two following days. The sum of monoterpene emissions was 4–23 times higher compared to emissions prior to the hailstorm while MBO emissions remained unchanged. The monoterpene emission (in mg compound m −2 ) during this measurement period is underestimated by 40% if the effect of this disturbance source is not considered.