Development and Application of a Relaxed Eddy Accumulation (REA) System to Measure Vertical Fluxes of Nitrous Acid (HONO)

近年来，亚硝酸（HONO）已被确定为低层大气中OH自由基的主要来源。由于OH自由基负责降解大多数空气污染物和形成有害的光氧化剂，例如臭氧，因此HONO来源的识别和量化非常重要。基于实验室研究，主要假设HONO的地面来源来解释白天低层大气中出乎意料的高水平。然而，由此产生的通量测量HONO在周围的表面只是很少。此外，由于缺乏快速和灵敏的HONO测量方法，通常只应用空气动力学梯度法，导致大气中HONO垂直通量的量化存在很大的不确定性。因此，REA（松弛涡流积累）系统应在本项目中开发和测试。应使用基于LOPAP（长路径吸收光度计）方法并与微气象入口系统耦合的双通道仪器。由超声波风速计控制的两个快速电磁阀用于探测上升和下降气流的两个通道。此外，第三个测量通道用于校正化学干扰。除了建立REA仪器外，还将开发一种新的控制进气阀和微气象数据记录的软件。新的REA系统将首先针对BUW的敏感通量测量进行测试和优化。到项目结束时，将在格里尼翁（法国）的一个农业现场的裸露土壤上测量HONO通量和其他辅助参数，以确定和量化大气中HONO的日间来源。所获得的数据应与申请人以前的DFG项目的结果进行比较，在该项目中，HONO通量是在同一测量地点用更简单的空气动力学梯度法确定的。

During recent years Nitrous Acid (HONO) has been identified as a dominant source of OH radicals in the lower atmosphere. Since the OH radical is responsible for the degradation of most air pollutants and for the formation of harmful photooxidants, e.g. ozone, the identification and quantification of the sources of HONO are of major importance. Based on laboratory studies mainly ground surface sources of HONO were postulated to explain the un-expected high daytime levels in the lower atmosphere. However, resulting flux measurements of HONO over ambient surfaces are only rarely available. In addition, only the aerodynamic gradient method is typically applied, caused by the absence of fast and sensitive HONO measurements methods, resulting in significant uncertainties in the quantification of vertical fluxes of HONO in the atmosphere. Thus, a REA (Relaxed Eddy Accumulation) system should be developed and tested in the present project. A two channel instrument should be used which is based on the LOPAP (Long Path Absorption Photometer) approach and which is coupled to a micrometeorological inlet system. Two fast magnetic valves controlled by an ultrasonic anemometer are used to probe the two channels for up- and downdraft air masses. In addition, a third measurement channel is used to correct for chemical interferences. Besides setting-up of the REA instrument, a new software for controlling the inlet valves and for micrometeorological data logging will be developed. The new REA system will be first tested and optimized for sensitive flux measurements at the BUW. To the end of the project, HONO fluxes and supporting other parameters will be measured over bare soil at an agriculture field site in Grignon (France) in two campaigns to identify and quantify daytime sources of HONO in the atmosphere. The obtained data should be compared with results from a former DFG-project of the applicant in which HONO fluxes were determined by the more simple aerodynamic gradient method at the same measurement site.