A controlling role for the air−sea interface in the chemical processing of reactive nitrogen in the coastal marine boundary layer
A controlling role for the air−sea interface in the chemical processing of reactive nitrogen in the coastal marine boundary layer
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DOI：
10.1073/pnas.1318694111
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发表时间：
2014-03
期刊：
影响因子：
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通讯作者：
Michelle J. Kim;D. Farmer;T. Bertram
中科院分区：
文献类型：
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作者：
Michelle J. Kim;D. Farmer;T. Bertram
在海气界面发生的反应有可能改变大气的化学成分。然而，我们对这些反应对氧化剂及其前体浓度的影响程度的了解来自于实验室测量，使用的系统模拟了海洋表面的化学、生物和物理复杂性。在这里，我们使用涡流相关和化学电离飞行时间质谱法对反应物-生成物对的垂直通量进行了直接测量，以直接评估海洋表面在活性氮和卤素交换中的作用。我们的观测结果表明，海洋表面在控制N2O5的寿命方面起着关键作用，N2O5是对流层活性氮的主要夜间储存库。海洋边界层中活性氮的寿命和活性卤素的生成速率受到水界面反应的强烈影响。尽管海气界面作为反应表面具有潜在的重要性，但很少有直接的现场观测可以评估其对反应氮沉积和卤素活化的影响。在这里，我们提出了对反应物-产物对N2O5和ClNO2的垂直通量的直接测量，以评估海洋表面在活性氮和卤素交换中的作用。我们测量了夜间N2O5交换速度（Vex = - 1.66±0.60 cm s - 1），该速度受N2O5向空气-海洋界面的大气输送的限制。令人惊讶的是，N2O5反应吸收产物ClNO2的垂直通量显示净沉积，这表明在海洋边界层中发现的ClNO2混合比的升高主要是由N2O5与气溶胶颗粒的反应维持的。实测沉积速率与N2O5对气溶胶颗粒反应性吸收的现场观测结果的比较表明，N2O5沉积到海洋表面占总损失率的26%至42%。大Vex、N2O5和ClNO2的净沉积共同作用，通过缩短N2O5的夜间寿命来限制NOx的再循环率和Cl原子的产生。这些结果表明，在受污染的沿海地区，空气-海洋交换过程占夜间NOx去除量的15%，并可将日出时ClNO2浓度降低20%以上。
Significance Reactions occurring at the air−sea interface have the potential to alter the chemical composition of the atmosphere. However, our knowledge of the extent to which these reactions impact the concentration of oxidants and their precursors is derived from laboratory measurements using systems that mimic the chemical, biological, and physical complexity of the surface ocean. Here, we present direct measurements of the vertical fluxes of a reactant−product pair using eddy covariance coupled with chemical ionization time-of-flight mass spectrometry to directly assess the role of the ocean surface in the exchange of reactive nitrogen and halogens. Our observations suggest that the ocean surface plays a critical role in controlling the lifetime of N2O5, a primary nocturnal reservoir for tropospheric reactive nitrogen. The lifetime of reactive nitrogen and the production rate of reactive halogens in the marine boundary layer are strongly impacted by reactions occurring at aqueous interfaces. Despite the potential importance of the air−sea interface in serving as a reactive surface, few direct field observations are available to assess its impact on reactive nitrogen deposition and halogen activation. Here, we present direct measurements of the vertical fluxes of the reactant−product pair N2O5 and ClNO2 to assess the role of the ocean surface in the exchange of reactive nitrogen and halogens. We measure nocturnal N2O5 exchange velocities (Vex = −1.66 ± 0.60 cm s−1) that are limited by atmospheric transport of N2O5 to the air−sea interface. Surprisingly, vertical fluxes of ClNO2, the product of N2O5 reactive uptake to concentrated chloride containing surfaces, display net deposition, suggesting that elevated ClNO2 mixing ratios found in the marine boundary layer are sustained primarily by N2O5 reactions with aerosol particles. Comparison of measured deposition rates and in situ observations of N2O5 reactive uptake to aerosol particles indicates that N2O5 deposition to the ocean surface accounts for between 26% and 42% of the total loss rate. The combination of large Vex, N2O5 and net deposition of ClNO2 acts to limit NOx recycling rates and the production of Cl atoms by shortening the nocturnal lifetime of N2O5. These results indicate that air−sea exchange processes account for as much as 15% of nocturnal NOx removal in polluted coastal regions and can serve to reduce ClNO2 concentrations at sunrise by over 20%.