The roles of volatile organic compound deposition and oxidation mechanisms in determining secondary organic aerosol production: a global perspective using the UKCA chemistry-climate model (vn8.4)
The roles of volatile organic compound deposition and oxidation mechanisms in determining secondary organic aerosol production: a global perspective using the UKCA chemistry-climate model (vn8.4)
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DOI：
10.5194/gmd-12-2539-2019
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发表时间：
2019-06-28
影响因子：
5.1
通讯作者：
Liu, Dantong
中科院分区：
文献类型：
--
作者：
Kelly, Jamie M.;Doherty, Ruth M.;Liu, Dantong
在英国化学和气溶胶（UKCA）化学气候模式中，发展了二次有机气溶胶（SOA）形成背景下挥发性有机化合物（VOC）沉积和氧化机制的表示。这些发展对全球SOA预算和模型与观测结果的一致性的影响进行了量化。首先，全球模式进行模拟与不同的VOC干沉降和湿沉降通量。包括VOC干沉积使全球年度总SOA生产率降低2%-32%，其范围反映了表面电阻的不确定性。包括VOC湿沉降减少了全球annualtotal SOA生产率的15%，是相对不敏感的有效亨利定律系数的变化。在没有前体沉积的情况下，模拟的SOA浓度低于在归一化平均偏差（NMB）为-51%的情况下观察到的浓度。因此，包括SOA前体沉积使模型与观测结果的一致性更进一步（NMB =-66%）。其次，对于人为和生物质燃烧的挥发性有机化合物的前体SOA（VOCANT/BB），模型模拟进行了（a）不同的母烃反应性，（B）不同的反应中间体的数量，和（c）占不同途径的氧化产物之间的挥发性差异。将这些变化与其中VOCANT/BB采用单萜（β-蒎烯）的反应性并且以具有固定SOA产率的单步机制氧化的方案进行比较。通过使用苯、甲苯或萘对V0 CANT/BB的化学反应性，与使用ff-pinene时相比，全球年总V0 CANT/BB氧化速率分别变化3%、31%或66%。通过引入过氧自由基（RO 2）来增加反应中间体的数量，略微减缓了SOA的形成速率，但对全球年度总SOA生产速率没有影响。然而，RO 2经历竞争性氧化反应，形成具有显著不同挥发性的产物。考虑到RO 2氧化途径之间的产物挥发性差异，与使用单一SOA产量相比，全球SOA生产率增加了153%。总体而言，对于甲苯和萘等相对反应性的化合物，考虑到RO 2产品挥发性的差异，VOCANT/BB氧化反应性的降低超过了RO 2产品挥发性的降低，导致全球年度总SOA生产率分别净增加85%和145%，模型一致性改善（NMB分别为46%和56%）。然而，对于苯，由于SOA产率途径的差异，VOCANT/BB氧化的减少并没有超过，导致全球年总SOA生产率发生3%的微小变化，模型与观测结果的一致性略有恶化（NMB = -77%）。这些结果突出表明，VOC沉积和氧化机制的变化导致全球SOA预算和模型与观测结果的一致性存在很大的不确定性。
The representation of volatile organic compound (VOC) deposition and oxidation mechanisms in the context of secondary organic aerosol (SOA) formation are developed in the United Kingdom Chemistry and Aerosol (UKCA) chemistry-climate model. Impacts of these developments on both the global SOA budget and model agreement with observations are quantified. Firstly, global model simulations were performed with varying VOC dry deposition and wet deposition fluxes. Including VOC dry deposition reduces the global annual-total SOA production rate by 2 %-32 %, with the range reflecting uncertainties in surface resistances. Including VOC wet deposition reduces the global annualtotal SOA production rate by 15% and is relatively insensitive to changes in effective Henry's law coefficients. Without precursor deposition, simulated SOA concentrations are lower than observed with a normalised mean bias (NMB) of -51 %. Hence, including SOA precursor deposition worsens model agreement with observations even further (NMB = -66 %). Secondly, for the anthropogenic and biomass burning VOC precursors of SOA (VOCANT/BB), model simulations were performed by (a) varying the parent hydrocarbon reactivity, (b) varying the number of reaction intermediates, and (c) accounting for differences in volatility between oxidation products from various pathways. These changes were compared to a scheme where VOCANT/BB adopts the reactivity of a monoterpene (ff -pinene), and is oxidised in a singlestep mechanism with a fixed SOA yield. By using the chemical reactivity of either benzene, toluene, or naphthalene for VOCANT/BB, the global annual-total VOCANT/BB oxidation rate changes by 3 %, 31 %, or 66 %, respectively, compared to when using ff -pinene. Increasing the number of reaction intermediates, by introducing a peroxy radical (RO2), slightly slows the rate of SOA formation, but has no impact on the global annual-total SOA production rate. However, RO2 undergoes competitive oxidation reactions, forming products with substantially different volatilities. Accounting for the differences in product volatility between RO2 oxidation pathways increases the global SOA production rate by 153% compared to using a single SOA yield. Overall, for relatively reactive compounds such as toluene and naphthalene, the reduction in reactivity for VOCANT/BB oxidation is outweighed by accounting for the difference in volatility of RO2 products, leading to a net increase in the global annual-total SOA production rate of 85% and 145 %, respectively, and improvements in model agreement (NMB of 46% and 56 %, respectively). However, for benzene, the reduction in VOCANT/BB oxidation is not outweighed by accounting for the difference in SOA yield pathways, leading to a small change in the global annual-total SOA production rate of 3 %, and a slight worsening of model agreement with observations (NMB = -77%). These results highlight that variations in both VOC deposition and oxidation mechanisms contribute to substantial uncertainties in the global SOA budget and model agreement with observations.