Retrieval Of Nitrogen Dioxide Total Column Over China From SCIAMACHY/ENVISAT Data

Nitrogen dioxide is an important trace gas in the atmosphere. It is mainly in stratosphere and troposphere. Nitrogen dioxide has an important effect on stratospheric and tropospheric chemistry. In the stratosphere, it is involved in ozone depletion and reacts with halogen oxide. In the troposphere, NO2 is a one of most important ozone precursors and locally also contributes to radiative forcing. It also could infect human health with its strong corrosiveness. Although the concentration of NO2 is high in the stratosphere, it is relatively stable. On the contrary, the concentration of NO2 is low in the troposphere while it can strongly influence by anthropogenic activities. Consequently, the change of nitrogen dioxide in the troposphere becomes a hot research topic currently.Monitoring atmospheric constituents from space is a hot issue. Since 1990's, there are more 20 projects focusing on satellite atmospheric chemistry observation. For example, European satellite ENVISAT and American satellite AURA are all platform for atmospheric chemistry remote sensing. By using of the observation data from the high spectrum resolution atmospheric constituent instruments on-board, European and American scientists have gotten the spatial and temporal pattern of NO2 more than ten years and on the global scale. At present, China has begun to design our own plan to develop the space-base instrument to monitoring the atmospheric constituents. However, both of the instruments designing and the retrieval algorithm research and quantity application of remote sensing data are all still in a start stage in China.In this paper, the current space-based instruments on atmospheric constituent remote sensing, the retrieval algorithm on nitrogen dioxide, and the radiation transfer model with the high spectrum resolution have been summarized first. The operational modes, the data preprocessing method and the data format of SCIAMACHY/ENVISAT, the well-developed atmospheric radiation transfer model SCIATRAN, Differential Optical Absorption Spectroscoy (DOAS) have been introducted. Based on above works, the sensitivity study of NO2, the retrieval algorithm of NO2, and the validation of retrieval results are performed.In the NO2 sensitivity analysis, we chose the SCIATRAN model, which can be used to process absorption and scattering effect in ultraviolet and visible spectrum with very high accuracy, to simulate and to analyze the effect of atmospheric aerosol,surface albedo and trace gas concentration changing on NO2 retrieval from 425-450 nm spectrum observed by SCIAMACHY. Based on DOAS method with the differential process on reflected spectrum,the slow changed part in reflected spectrum caused by aerosol and surface albedo are eliminated. And the residual error after DOAS processing has been discussed. The results show that three factors have different effects on the spectrum before and after differential processing. Before differential processing, surface albedo is the biggest influence factor, then is aerosol and aimed gas; after differential processing, the biggest factor is aimed gas, then is surface albedo and aerosol. The results also show that differential absorption spectrum still has residual error caused by surface albedo and aerosol after DOAS process. Hence, the more careful correction for surface albedo and aerosol is requried to retrieve atmospheric constituent concentration from observed solar reflected spectrum by satellite.In the retrieval method research, considering absorption characteristic of NO2,O3,O4,H2O and Ring effect, based on DOAS method, using least square fitted slant columns, with AMF calculated by experience formula, this paper has gotten NO2 vertical columns in the fitting window 425-450nm. The month mean NO2 vertical columns distribution figures are gotten by using April, July and October of 2004 SCIAMACHY L1b data which are from"Dragon Programme".These three months retrieval results have a good consistency in large value distribution. Furthermore, validations between retrieval result and European level 2 productions have been done about NO2 slant columns and vertical columns. The results are: retrieved NO2 slant columns and vertical columns have a good match with European level 2 productions. In value,NO2 slant columns'relative error is smaller, and has a latitude band distribution. From south to north, error is become small, except Qinghai-Tibet Plateau. This is mainly caused by temperature dependency of NO2 cross section while large error between assumed and real atmosphere. NO2 vertical columns'error is much bigger, special in NO2 big value and continential in low latitude. It is because the error of vertical columns contain tow parts slant error and AMF error. While AMF in this paper is calculated by experience formula, not considering effect of absorption and scattering. Thus, it appears big value in high NO2 concentration and the aero has huge water vapor or large aerosol loading. Based on this validation result, in retrieval of NO2 vertical columns, temperature of cross section and simulated AMF all could result in big error, they are needed precision correction.In validation of result, SCIAMACHY L1b data used to retrieval are just three month, and incontinuity. Thus, the validation is used European productions and ground_base data in Beijing from January 2000 to October 2006. Result is in a good consistency.This research result could be a good base for future developing Chinese own satellite atmospheric constituent instrument, expanding nitrogen dioxide retrieval method and application of the production.