Detection of the trend and seasonal variation in tropospheric NO₂ over China

Abstract

The results of a trend study on the tropospheric NO 2 column over China are presented, on the basis of measurements from the satellite instruments GOME and SCIAMACHY. From these observations, monthly averaged tropospheric NO 2 distributions are determined for the period 1996 to 2005 on a 1° by 1° grid. A linear model with a seasonal component is used to fit these time series. The variance and the autocorrelation of the noise are used to calculate the significance of the trend. The results show a large growth of tropospheric NO 2 over eastern China, especially above the industrial areas with a fast economical growth. For instance, Shanghai had a linear significant increase in NO 2 columns of 20% ± 6% per year (reference year 1996) in the period 1996–2005. The seasonal pattern of the NO 2 concentration shows a difference between east and west China. In the east a NO 2 maximum is found during wintertime, because of chemistry and anthropogenic activity. Contrary to this, in the western part of China the NO 2 concentration reaches a maximum in summertime. This spatial difference correlates with the population distribution of China. Since there is negligible anthropogenic activity in west China this difference in seasonality of NO 2 is attributed to natural emissions in west China.