Seasonality of isoprene emissions and oxidation products above the remote Amazon
Seasonality of isoprene emissions and oxidation products above the remote Amazon
复制标题
DOI：
10.1039/d1ea00057h
复制
发表时间：
2022-03-01
期刊：
影响因子：
--
通讯作者：
Nemitz, E.
中科院分区：
文献类型：
--
作者：
Langford, B.;House, E.;Nemitz, E.
亚马逊雨林是全球异戊二烯排放的最大来源。在低一氧化氮(NO)条件下(即NO混合比小于40PPTV)，异戊二烯与羟基(OH)迅速反应生成异戊二烯衍生的过氧化氢自由基(ISOPOO)，再与羟基过氧化氢自由基(HO2)反应生成异戊二烯环氧二醇(IEPOX)。IEPOX化合物是形成二次有机气溶胶的有效前体。因此，天然异戊二烯排放有可能影响云量、降雨量、辐射平衡和气候。在这里，我们提出了第一个季节分析的异戊二烯排放和浓度以上亚马逊基于涡旋协方差通量测量在一个偏远的森林位置。结果表明，森林全年异戊二烯的排放潜力保持恒定(6.9mgm~(-2)h~(-1))。通过将测量的通量归一化到一组标准条件(303K和1500mmolm(-2)S(-1))来计算异戊二烯的排放潜力。在雨季，观察到绝对排放量减少了两倍，但这完全是基于气象和叶面积指数，而不是异戊二烯排放潜力的变化。通过对异戊二烯通量的创新分析，结合对其氧化产物的测量和详细的化学盒模拟，我们探索了IEPOX的浓度是否遵循与异戊二烯前体相同的季节周期。我们的分析表明，在旱季(9月至1月)，区域生物质燃烧造成的空气污染提供了NO浓度的适度增加(从其他人为示踪测量和盒子模拟的组合中间接推断)，这为ISOPOO创造了一条竞争的氧化途径；替代产物不是形成IEPOX，而是形成不太容易产生气溶胶的替代产物。与没有人为无污染的情况相比，这项竞争在旱季将IEPOX的形成率降低了两倍，全年降低了30%。亚马逊地区生物来源的SOA前体的丰度似乎并不像以前认为的那样由天然异戊二烯排放的季节性决定，而是由改变异戊二烯大气化学的区域人为污染驱动的。
The Amazon rainforest is the largest source of isoprene emissions to the atmosphere globally. Under low nitric oxide (NO) conditions (i.e. at NO mixing ratios less than about 40 pptv), isoprene reacts rapidly with hydroxyl (OH) to form isoprene-derived peroxy radicals (ISOPOO), which subsequently react with the hydroperoxyl radical (HO2) to form isoprene epoxydiols (IEPOX). IEPOX compounds are efficient precursors to the formation of secondary organic aerosols (SOA). Natural isoprene emissions, therefore, have the potential to influence cloudiness, rainfall, radiation balance and climate. Here, we present the first seasonal analysis of isoprene emissions and concentrations above the Amazon based on eddy covariance flux measurements made at a remote forest location. We reveal the forest to maintain a constant emission potential of isoprene throughout the year (6.9 mg m(-2) h(-1)). The emission potential of isoprene is calculated by normalising the measured fluxes to a set of standard conditions (303 K and 1500 mu mol m(-2) s(-1)). During the wet season a factor of two reduction in absolute emissions was observed but this is explained entirely on the basis of meteorology and leaf area index, not by a change in isoprene emissions potential. Using an innovative analysis of the isoprene fluxes, in combination with measurements of its oxidation products and detailed chemical box-modelling, we explore whether concentrations of IEPOX follow the same seasonal cycle as the isoprene precursor. Our analysis implies that during the dry season (Sep-Jan) air pollution from regional biomass burning provides a modest increase in NO concentrations (indirectly inferred from a combination of other anthropogenic tracer measurements and box-modelling) which creates a competing oxidation pathway for ISOPOO; rather than forming IEPOX, alternative products are formed with less propensity to produce aerosol. This competition decreases IEPOX formation rates by a factor of two in the dry season compared with a scenario with no anthropogenic NO pollution, and by 30% throughout the year. The abundance of biogenic SOA precursors in the Amazon appears not to be dictated by the seasonality of natural isoprene emissions as previously thought, but is instead driven by regional anthropogenic pollution which modifies the atmospheric chemistry of isoprene.