临近空间飞行平台青藏高原大气NO_(x)原位观测实验

In situ observation of atmospheric NO_(x) over Qinghai-Tibet Plateau by Scientific Experiment System in Near Space Program

大气NO_(x)气体分析仪是中国科学院战略性先导科技专项“临近空间科学实验系统”“太阳风暴在临近空间环境的响应”任务的主载荷之一,是我国自主研发的原位探测临近空间大气NO_(x)的载荷,并已成功测量临近空间高空气球飞行路径NO、NO_(2)、NO_(x)混合比.分析仪基于可见-紫外光谱吸收法原理,用动态流导法将飞行路径上1×103~1×10^(5) Pa的自然大气压缩至8×10^(4)~1×10^(5) Pa,构建了长期稳定的常压工作环境,把商用氮氧化物光谱仪的适用范围从地表拓展到高空.2019和2020年夏季,中纬度青藏高原大柴旦地区开展的两次高空气球科学实验均搭载了大气NO_(x)气体分析仪,实现了对流层5 km到平流层30 km大气NO_(x)的原位测量,并获取了青藏高原上空NO、NO_(2)、NO_(x)混合比的科学探测数据.

The atmospheric NO_(x) gas analyzer(ANG)is the self-developed near-space instrument for in situ NO_(x) measurement by China.As one of the primary payloads of the Scientific Experiment System in Near Space program of the Chinese Academy of Sciences,the ANG successfully measured the mix ratios of NO,NO_(2),and NO_(x).The Model 405 nm NO_(x) monitor(2B Technologies,USA)is a commercial NO_(x) analyzer that can only operate in normal pressure and temperature.Based on the dynamic flow method,we designed a vacuum system to compress the ambient environment from 1×103–1×10^(5) to 8×10^(4)–1×10^(5) Pa and to ensure the long-term stable operational environment for the Model 405 nm NO_(x) analyzer,expanding its application range from the Earth’s surface to near space.To ensure the validity of the scientific data collected,we carried out separate ground calibration experiments for the Model 405 nm NO_(x) analyzer and ANG.The calibration results of the commercial analyzer show that the deviation of NO is less than 0.1%and the uncertainty is approximately 1.7%,while the deviation of measured NO_(2) is less than 0.5%and the uncertainty is approximately 5.3%.The observation upper and lower limits of NO and NO_(2) are both in the range 0–1000 ppbv.According to the calibration results of the ANG,the deviation between the calibration and standard values of the mix ratio of NO and NO_(2) ranges from approximately−0.2 to+0.6 ppbv.The stability test results of the ANG show that it can operate stably in the stratosphere for more than 24 h.In addition,we analyzed the influence of compressed atmospheric pressure by the vacuum system on the measurement results.It was further found that for ANG,the error in the NO mix ratio is in the range of 1.5%–25%.The above results show that the ANG can meet atmospheric gas-analysis requirements.In the summers of 2019 and 2020,two high-altitude balloon scientific flight experiments with the ANG were carried out in Dachaidan(95°E,37°N)on the Qinghai-Tibet Plateau,and scientific data of the NO_(x) mix ratio on the flight path from the troposphere to the 20–30 km level of the stratosphere were obtained.To the best of our knowledge,in this paper,we present the first in situ measurement results of the NO_(x) mix ratio at 5–30 km above the Qinghai-Tibet Plateau in the middle latitude.From the end of August to the beginning of September 2019 and 2020,the average value of the NO mix ratio at 10–25 km was approximately 0.5 ppbv,that of the NO_(2) mix ratio approximately 3.1 ppbv,and that of the NO_(x) mix ratio approximately 3.6 ppbv.The mix ratio of NO_(2) in the summer of 2020(specifically,in September)was higher than that of NO.The peak of the NO mix ratio occurred at~8 km and the minimum value of the NO_(2) mix ratio occurred at~15 km.The mix ratio profiles of NO and NO_(2) were influenced by sunlight and atmospheric temperature.The low NO mix ratio values were preserved during the balloon’s rising process.At 9–15 km,the profiles exhibited the same tendency between the NO_(2) mix ratio and ambient atmospheric temperature,with a correlation of approximately 98.8%.However,below 10 km the NO_(x) mix ratio exhibited the same trends as those of NO.The above results show that photolysis did not dominate during this period.These observations are consistent with atmospheric physics.During periods of high solar activity,ANG measurements can be used to study solar storm effects on near-space NO_(x).