Airborne flux measurements of biogenic isoprene over California
Airborne flux measurements of biogenic isoprene over California
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加利福尼亚州上空生物异戊二烯的空气通量测量
DOI：
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发表时间：
2014
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通讯作者：
A. Goldstein
中科院分区：
文献类型：
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作者：
P. Misztal;P. Misztal;T. Karl;T. Karl;R. Weber;H. Jonsson;A. Guenther;A. Guenther;A. Goldstein
摘要。作为2011年6月加州自然生态系统样带（CABERNET）机载生物源性挥发性有机化合物（BVOC）排放研究的一部分，生物源性异戊二烯通量在CIRPAS双水獭飞机上进行了测量。机载虚拟分离涡流相关（AvDEC）方法使用质子转移反应质谱仪（PTR-MS）和风天线罩探头测量，直接确定异戊二烯在7400公里飞行路径上的通量，重点是预计加州排放最大的地区。快速傅里叶变换（FFT）方法用于计算超过15公里的长断面上异戊二烯的通量，最常见的是在50至150公里之间。在相同的横断面上使用连续小波变换（CWT）方法计算瞬时异戊二烯通量，其局部化与非平稳无关，具有频率和时间。通量通常通过在400米±50米（a.g.l.）高度持续飞行来测量，并根据赛道堆叠剖面确定的通量散度外推到地表。小波衍生的异戊二烯地表通量平均为2 km空间分辨率，与用于驱动BVOC排放模型的基础发射因子（BEF）土地覆盖数据集具有良好的对应关系。异戊二烯的地表通量在中央谷地作物和荒漠灌丛地接近于零，而在栎林地则非常高（高达15 mg m−2 h−1），其排放量明显依赖于温度和栎树密度。在最炎热的日子和主要污染源地区上空，在飞机高度观测到异戊二烯浓度高达8 ppb。尽管来自农业种植区、灌丛地和针叶林的异戊二烯排放量极低，但在萨克拉门托以南的核桃树林塔的观测表明，来自周围橡树林地高排放区的异戊二烯氧化产物在夜间积聚在山谷上方的残余层中，并在早晨混合到山谷中。因此，山谷周围的异戊二烯排放与区域光化学有关，仅从直接排放通量分布不能立即看出这一点。本文报告了通过飞机上的涡动相关方差对特定源的通量的首次区域观测，这最终可以约束各州机构用于臭氧模拟的全州异戊二烯排放清单。虽然以前没有可用的方法来限制生物成因模型，但我们的结果提供了一个很好的了解加州异戊二烯的主要来源，它们的大小，以及它们是如何分布的。这组关于异戊二烯通量的数据对于评估可能的模型替代方案特别有用，这将在评估异戊二烯排放模型及其驱动变量数据集的另一篇论文中讨论。
Abstract. Biogenic isoprene fluxes were measured onboard the CIRPAS Twin Otter aircraft as part of the California Airborne Biogenic volatile organic compound (BVOC) Emission Research in Natural Ecosystem Transects (CABERNET) campaign during June 2011. The airborne virtual disjunct eddy covariance (AvDEC) approach used measurements from a proton transfer reaction mass spectrometer (PTR–MS) and a wind radome probe to directly determine fluxes of isoprene over 7400 km of flight paths focusing on areas of California predicted to have the largest emissions. The fast Fourier transform (FFT) approach was used to calculate fluxes of isoprene over long transects of more than 15 km, most commonly between 50 and 150 km. The continuous wavelet transformation (CWT) approach was used over the same transects to also calculate instantaneous isoprene fluxes with localization of both frequency and time independent of non-stationarities. Fluxes were generally measured by flying consistently at 400 m ± 50 m (a.g.l.) altitude, and extrapolated to the surface according to the determined flux divergence determined in the racetrack-stacked profiles. The wavelet-derived surface fluxes of isoprene averaged to 2 km spatial resolution showed good correspondence to basal emission factor (BEF) land-cover data sets used to drive BVOC emission models. The surface flux of isoprene was close to zero over Central Valley crops and desert shrublands, but was very high (up to 15 mg m−2 h−1) above oak woodlands, with clear dependence of emissions on temperature and oak density. Isoprene concentrations of up to 8 ppb were observed at aircraft height on the hottest days and over the dominant source regions. Even though the isoprene emissions from agricultural crop regions, shrublands, and coniferous forests were extremely low, observations at the Walnut Grove tower south of Sacramento demonstrate that isoprene oxidation products from the high emitting regions in the surrounding oak woodlands accumulate at night in the residual layer above the valley and mix down into the valley in the morning. Thus, the isoprene emissions surrounding the valley have relevance for the regional photochemistry that is not immediately apparent solely from the direct emission flux distribution. This paper reports the first regional observations of fluxes from specific sources by eddy covariance from an aircraft which can finally constrain statewide isoprene emission inventories used for ozone simulations by state agencies. While previously there was no available means to constrain the biogenic models, our results provide a good understanding of what the major sources of isoprene are in California, their magnitude, and how they are distributed. This data set on isoprene fluxes will be particularly useful for evaluating potential model alternatives which will be dealt with in a separate paper to assess isoprene emission models and their driving variable data sets.