Abstract
Abstract. Nitric oxide (NO) is a key active trace gas in the atmosphere, which contributes to form harmful ozone in the troposphere and to the destruction of ozone in the stratosphere. In this study, we present the NO retrieval from ground-based Fourier-transform infrared (FTIR) solar absorption spectrometry measurements at a polluted site (Xianghe, China) and a background site (Maïdo, Reunion Island). The degree of freedom (DOF) of the NO retrieval is 2.3±0.4 (1σ) at Xianghe and 1.3±0.1 at Maïdo. By looking at the FTIR NO retrievals at Xianghe and Maïdo, we find that the stratospheric NO partial column is large in summer as compared to winter at both sites, and the seasonal variation in the FTIR stratospheric NO partial columns is consistent with that observed by the co-located Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite measurements. A large diurnal variation in the stratospheric NO partial column is observed by the FTIR measurements at Maïdo, with an increase from the early morning to about 14:00 local time and a decrease thereafter. Due to the low NO concentration near the surface, the FTIR NO retrieval is only sensitive to the stratosphere at Maïdo. The high NO mole fraction near the surface at Xianghe allows us to derive tropospheric and stratospheric NO partial columns separately, although the tropospheric column is very difficult to retrieve in summer (June–August) because of the high water vapor abundance. A good correlation is found between the NO observed by the FTIR measurements and other air pollutants (NO2 and CO) in the troposphere at Xianghe. It is the first study of a successful analysis of NO in the troposphere from a ground-based FTIR site. The tropospheric and stratospheric NO retrieval might be possible at other potential FTIR sites inside or near large cities with enhanced levels of NO near the surface.
Highlights
Nitric oxide (NO) is a major component of the nitrogen oxide family (NOx = NO + NO2), which plays key roles in atmospheric chemistry
The Fourier-transform infrared (FTIR) retrievals are able to derive the diurnal variation in the NO partial column in the stratosphere during the daytime, especially at Maïdo
It is found that the stratospheric NO partial column increases with time in the morning to about 12:20 LT, and there is a linear relationship between the stratospheric NO partial column and the solar radiation intensity, with an R of 0.80 at Xianghe and 0.74 at Maïdo
Summary
Spaceborne sensors, e.g., the Atmospheric Chemistry Experiment–Fourier Transform Spectrometer (ACE–FTS) making solar occultation measurements (Bernath et al, 2005) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) looking at thermal emission at the limb (Fischer et al, 2008), can provide global NO distributions. These satellite measurements provide almost no information in the troposphere.
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