Atmospheric reactive nitrogen cycling over the ocean

海洋上空的大气活性氮循环

• 批准号: NE/S000518/1
• 负责人: Lucy Carpenter
• 金额: $ 78.79万
• 依托单位: University of York
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS000518%2F1
• 关键词: Atmospheric; reactive; nitrogen; cycling; over

Atmospheric chemical processing drives the removal of emitted pollutants, and leads to the formation of ozone and secondary aerosol, which are harmful to human and environmental health, and contribute to climate forcing. Quantitative understanding of such chemistry is essential for the accurate prediction of current air quality and future atmospheric composition.In the troposphere, gaseous chemical processing is critically dependent upon the abundance of nitrogen oxides (NOx, NO + NO2), which regulate atmospheric oxidising capacity, ozone formation and the major components of many aerosol particles. Globally, the dominant NOx sources are all continental (traffic, power generation, industry, soil emissions of NO); these are well understood in some locations, but are very uncertain and rapidly increasing in developing nations, particularly African megacities. Once in the atmosphere, NOx is converted to reservoir compounds such as PAN, which may release NOx after transport, and ultimately into nitric acid (HNO3) on timescales of days. Current understanding is that HNO3 is the final atmospheric sink for NOx, and is removed from the atmosphere by deposition. Consequently, at remote marine sites a number of days transit time from the coast, we would expect NOx levels to be very low, and the inorganic nitrogen budget to be dominated by unreactive transported HNO3.Recent observations challenge this understanding: surprisingly high levels of NOx species, and HONO (a NOx precursor with a lifetime of a few minutes) have been observed over the tropical Atlantic ocean. This points to a missing source of HONO and NOx. It has been hypothesised that the photolytic conversion of particle-bound nitrate to gaseous HONO and NO2 may account for these observations and form the missing NOx source - a mechanism termed "renoxification" (Ye et al., Nature 2016). We have performed proof-of-concept measurements and modelling of HONO and NOx levels at the Cape Verde observatory in the tropical Atlantic, which we have found to be consistent with this mechanism (Reed et al., ACP, 2017) - however, order of magnitude uncertainties over the rate and products of particle nitrate photolysis remain, and observational evidence for its occurrence on dominant aerosol species (dust, sulfate aerosol) is missing, meaning that impacts on the global-scale are unknown.This project aims to address these uncertainties, through integrating existing ground-based, aircraft and satellite observations with targeted new field and laboratory studies. We will focus upon a natural laboratory, the tropical Atlantic region where we will probe the emissions and evolution of nitrogen species in the outflow of polluted air from the developing regions of West Africa to the clean marine environment of the mid Atlantic (Cape Verde Observatory, CVO). Specifically, we will (1) Use the tropical Atlantic as a natural laboratory to study renoxification during different seasons and aerosol regimes, alongside laboratory studies to parameterise the particulate nitrate photolysis process; (2) integrate this new understanding into a global chemistry-transport model to evaluate the recycling and transformations of NOx during transport, and hence the impacts of these process in the tropical Atlantic ocean, and upon our understanding of atmospheric chemical processing globally.

大气化学处理促进了排放污染物的去除，并导致臭氧和二次气溶胶的形成，这对人类和环境健康有害，并有助于气候强迫。对此类化学的定量理解对于准确预测当前空气质量和未来大气成分至关重要。在对流层中，气态化学处理关键取决于氮氧化物（NOx、NO + NO2）的丰度，氮氧化物调节大气氧化能力，臭氧的形成和许多气溶胶颗粒的主要成分。在全球范围内，主要的氮氧化物来源都是大陆性的（交通、发电、工业、土壤排放的氮氧化物）；这些在一些地方是众所周知的，但在发展中国家，特别是非洲大城市，却非常不确定并且迅速增加。一旦进入大气，NOx 就会转化为 PAN 等储存化合物，在运输后可能会释放 NOx，并最终在数天的时间内转化为硝酸 (HNO3)。目前的认识是，HNO3 是 NOx 的最终大气汇，并通过沉积从大气中去除。因此，在距离海岸数天的偏远海洋地点，我们预计氮氧化物水平非常低，并且无机氮预算将由非反应性运输的硝酸主导。最近的观察挑战了这种理解：氮氧化物水平惊人地高物种和 HONO（一种寿命只有几分钟的氮氧化物前体）已在热带大西洋上空被观测到。这表明 HONO 和 NOx 的来源缺失。据推测，颗粒结合的硝酸盐光解转化为气态 HONO 和 NO2 可能解释了这些观察结果并形成了缺失的 NOx 源 - 一种称为“氧化”的机制（Ye 等人，Nature 2016）。我们在热带大西洋的佛得角天文台对 HONO 和 NOx 水平进行了概念验证测量和建模，我们发现这与这种机制一致（Reed 等人，ACP，2017） - 然而，顺序颗粒硝酸盐光解的速率和产物仍然存在很大的不确定性，并且缺少其在主要气溶胶物种（灰尘、硫酸盐气溶胶）上发生的观测证据，这意味着对全球范围的影响尚不清楚。该项目旨在通过将现有的地面、飞机和卫星观测与有针对性的新领域和实验室研究相结合来解决这些不确定性。我们将重点关注一个自然实验室，即热带大西洋地区，在那里我们将探测从西非发展中地区流出到大西洋中部清洁海洋环境的污染空气中氮物种的排放和演变（佛得角天文台， CVO）。具体来说，我们将（1）利用热带大西洋作为天然实验室来研究不同季节和气溶胶状态下的再氧化作用，同时进行实验室研究以参数化颗粒硝酸盐光解过程； (2) 将这一新的认识融入到全球化学传输模型中，以评估氮氧化物在传输过程中的循环和转化，从而评估这些过程对热带大西洋的影响，并基于我们对全球大气化学过程的理解。

项目成果

Long-term NOx measurements in the remote marine tropical troposphere

长期否

• DOI: http://dx.10.5194/amt-2020-469
• 发表时间: 2020
• 作者: Andersen S

Factors Influencing the Formation of Nitrous Acid from Photolysis of Particulate Nitrate.

影响颗粒硝酸盐光解形成亚硝酸的因素。

• DOI: http://dx.10.1021/acs.jpca.3c03853
• 发表时间: 2023
• 期刊: The journal of physical chemistry. A
• 作者: Sommariva R

Airborne observations over the North Atlantic Ocean reveal the importance of gas-phase urea in the atmosphere.

北大西洋上空的机载观测揭示了大气中气相尿素的重要性。

• DOI: http://dx.10.1073/pnas.2218127120
• 发表时间: 2023
• 期刊: Proceedings of the National Academy of Sciences of the United States of America
• 影响因子: 11.1
• 作者: Matthews E

Discovering global-scale processes in the marine atmosphere

发现海洋大气中的全球规模过程

• DOI: http://dx.10.5194/egusphere-egu24-11717
• 发表时间: 2024
• 作者: Carpenter L

Long-term NOx measurements in the remote marine tropical troposphere

长期否

• DOI: http://dx.10.5194/amt-14-3071-2021
• 发表时间: 2021
• 期刊: Atmospheric Measurement Techniques
• 影响因子: 3.8
• 作者: Andersen S