ATMOCHEM - PHOTOchemical Formation of Nitrous Acid in the Atmosphere (PHOTONA)

近几年来，亚硝酸(HONO)引起了人们极大的关注，因为最近的野外测量表明，HONO的光解可能是低层大气中OH自由基的主要来源。大部分空气污染物的降解和有害光氧化剂的形成都是由OH自由基引起的。因此，确定和量化HONO的来源是非常重要的。为了解释白天HONO浓度意外升高的原因，人们提出了不同的光化学来源。然而，受辐射的农村和城市表面上HONO通量的确切来源和大小仍然是悬而未决的问题，必须解决这些问题才能理解和量化大气的氧化能力。在拟议的项目中，这些问题的目的是通过选定的实验室、现场和模拟研究的综合来回答这些问题。在实验室研究中，将在光反应堆中利用非常灵敏和选择性的仪器来研究HONO的不同光化学源，以便能够模拟大气相关条件。在现场研究中，将在巴黎附近的一个现场(INRA/Grignon)利用混合梯度/涡旋协方差技术，在辐照表面上量化HONO的白天源强度，该技术自两年以来已经用于测量NOx和O3的通量。HONO通量将作为测量变量(太阳强度、NO2、硝酸盐等)的函数，针对不同类型的表面(例如，纯土壤和作物)进行参数化。此外，将在城市条件下在Forschungszentum Karlsruhe气象塔进行10-200米海拔范围内的白天梯度测量，以更好地量化HONO光解对扩展海拔范围的径向预算的影响。实验室和实地研究的结果--包括最近其他研究的数据--将用于改进现有的BOX、1-D和3-D模型，重点是更好地描述和量化边界层的氧化能力。该项目的结果将对理解低层大气的光化学产生重要影响。

Nitrous Acid (HONO) has attracted significant attention during the last few years since recent field measurements have demonstrated that the photolysis of HONO can be the dominant source of OH radicals in the lower atmosphere. The OH radical is responsible for the degradation of most air pollutants and for the formation of harmful photooxidants. Thus, the identification and quantification of the sources of HONO are of major importance. To explain unexpected high daytime concentrations of HONO, different photochemical sources have been proposed. However, the exact origin and the magnitude of HONO fluxes over irradiated rural and urban surfaces are still open questions, which have to be solved to understand and quantify the oxidation capacity of the atmosphere.In the proposed project, these questions are aimed to be answered by the integration of selected laboratory, field and modelling studies. In the laboratory studies, different photochemical sources of HONO will be investigated in photoreactors by the help of very sensitive and selective instrumentation to enable the simulation of atmospheric relevant conditions. In the field studies, the daytime source strength of HONO will be quantified over irradiated surfaces by the help of a mixed gradient / eddy-covariance technique at a field site near Paris (INRA/Grignon), which is already used for flux measurements of NOx and O3 since two years. The HONO fluxes will be parameterized for different types of surfaces (e.g. pure soil and crop) as a function of measured variables (solar intensity, NO2, nitrate, etc.). In addition, daytime gradients measurements in the altitude range 10-200 m will be performed under urban conditions at the meteorological tower at Forschungszentrum Karlsruhe to better quantification the impact of the HONO photolysis on the radical budget for an extended altitude range. The results from the lab and field studies - including data from recent other studies - will be used to improve existing box, 1-D and 3-D models with the focus on the better description and quantification of the oxidation capacity of the boundary layer. The outcome of the project will have an essential impact on the understanding of the photochemistry of the lower atmosphere.