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自由基负责大多数空气污染物的降解和有害光氧化剂（如臭氧）的形成，因此鉴定和量化HONO的来源非常重要。在实验室研究的基础上，主要假定HONO的地面源来解释低层大气中日间未预料到的高水平。然而，由此产生的在环境表面上的HONO通量测量很少可用。此外，由于缺乏快速灵敏的HONO测量方法，通常只采用气动梯度法，导致大气中HONO垂直通量的量化存在很大的不确定性。因此，在本工程中应开发和测试一个REA（松弛涡积）系统。应使用基于LOPAP（长路径吸收光度计）方法的双通道仪器，并与微气象入口系统耦合。两个由超声波风速计控制的快速电磁阀用于探测两个通道的上升和下降气流团。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，还将开发用于控制入口阀门和微气象数据记录的新软件。新的REA系统将首先在BUW进行敏感通量测量的测试和优化。在项目结束时，将在法国格里尼翁（Grignon）的一个农田的裸露土壤上测量HONO通量和其他支持性参数，以确定和量化大气中白天HONO的来源。获得的数据应与申请人以前的dfg项目的结果进行比较，其中在同一测量地点使用更简单的气动梯度法确定HONO通量。

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.