Nitrogen oxides (NO _x ) emitted from human activities are believed to regulate the atmospheric oxidation capacity of the troposphere. However, observational evidence is limited for the low-to-median NO _x concentrations prevalent outside of polluted regions. Directly measuring oxidation capacity, represented primarily by hydroxyl radicals (OH), is challenging, and the span in NO _x concentrations at a single observation site is often not wide. Concentrations of isoprene and its photo-oxidation products were used to infer the equivalent noontime OH concentrations. The fetch at an observation site in central Amazonia experienced varied contributions from background regional air, urban pollution, and biomass burning. The afternoon concentrations of reactive nitrogen oxides (NO _y ), indicative of NO _x exposure during the preceding few hours, spanned from 0.3 to 3.5 parts per billion. Accompanying the increase of NO _y concentration, the inferred equivalent noontime OH concentrations increased by at least 250% from 0.6 × 10⁶ to 1.6 × 10⁶ cm^-3. The conclusion is that, compared to background conditions of low NO _x concentrations over the Amazon forest, pollution increased NO _x concentrations and amplified OH concentrations, indicating the susceptibility of the atmospheric oxidation capacity over the forest to anthropogenic influence and reinforcing the important role of NO _x in sustaining OH concentrations.

中文翻译：

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异戊二烯光氧化产物可量化污染对亚马逊地区羟基自由基的影响。

人们认为，人类活动所排放的氮氧化物（NO _x）调节了对流层的大气氧化能力。然而，观测证据被限制为低到中值NO _X浓度普遍污染区域的外部。直接测量主要由羟基自由基（OH）表示的氧化能力具有挑战性，并且NO _x的跨度 单个观察点的浓度通常不宽。异戊二烯及其光氧化产物的浓度用于推断等效的正午时间OH浓度。亚马逊河中部一个观测点的取水经历了区域背景空气，城市污染和生物质燃烧的各种贡献。活性氮氧化物（NO下午浓度_Ý），表示NO的_X在之前的几个小时内，从每十亿0.3至3.5份跨越曝光。随着NO _y浓度的增加，推断的等效正午时间OH浓度从0.6×10 ⁶增至1.6×10 ⁶ cm ^-3至少增加了250％。 。结论是，相对于低NO的背景条件_X浓度超过亚马逊森林，污染增加的NO _X浓度和扩增OH浓度，表明在森林人为影响大气氧化能力的易感性和增强NO的重要作用_x表示维持的OH浓度。