Analysis of linear long-term trend of aerosol optical thickness derived from SeaWiFS using BAER over Europe and South China

Abstract

Abstract. The main purposes of the present paper are not only to investigate linear long-term trends of Aerosol Optical Thickness (AOT) at 443 and 555 nm over regions in Europe and South China, but also to show the uncertainty caused by cloud disturbance in the trend analysis of cloudfree aerosol. These research areas are the densely urbanised and often highly polluted regions. The study uses the Bremen AErosol Retrieval (BAER) and Sea-viewing Wide Field-ofview Sensor (SeaWiFS) data for AOT retrievals in the specified regions from October 1997 to May 2008. In order to validate the individually retrieved AOTs and the corresponding trends, AErosol RObotic NETwork (AERONET) level 2.0 data have been used. The retrieved AOTs were in good agreement with those of AERONET (0.79 ≤ R ≤ 0.88, 0.08 ≤ RMSD ≤ 0.13). The contamination of the aerosol retrievals and/or AERONET observations by thin clouds can significantly degrade the AOT and lead to statistically nonrepresentative monthly-means, especially during cloudy seasons. Therefore an inter-correction method has been developed and applied. The "corrected" trends for both BAER SeaWiFS and AERONET AOT were similar and showed in average a relative difference of ∼25.19 %. In general terms, negative trends (decrease of aerosol loading) were mainly observed over European regions, with magnitudes up to −0.00453 and −0.00484 yr −1 at 443 and 555 nm, respectively. In contrast, the trend in Pearl River Delta was positive, most likely attributed to rapid urbanization and industrialization. The magnitudes of AOT increased by +0.00761 and +0.00625 yr −1 respectively at 443 and 555 nm.

Model-simulated trend of surface carbon monoxide for the 2001–2010 decade

“…10. As a result of environmental regulations over these regions in past decades (Streets et al, 2003;Yoon et al, 2011Yoon et al, , 2012Yoon et al, , 2014, the decreasing trends of atmospheric aerosol and short-lived trace gases have been reported in many studies (e.g., Smith et al, 2001;Streets et al, 2006;Richter et al, 2005;Hilboll et al, 2013). The dramatic decrease in EMAC surface CO is estimated to be −59.6 ± 9.1 ppbv decade −1 for EUSA and −35.5 ± 5.8 ppbv decade −1 for WE and is compatible (see Fig.…”

“…In the realistic simulation RG (Fig. 8b), decreasing trends are generally predominant, in particular over Europe and the eastern USA as a result of strict environmental regulation (Streets et al, 2003;Yoon et al, 2011Yoon et al, , 2014Hilboll et al, 2013) and over southeastern Asia due to less fire activity . They are consistent with the WDCGG-archived trends (see Sect.…”

“…The eastern USA (EUSA) and western Europe (WE) are highly industrialized regions (Zhang et al, 2012;Yoon et al, 2011), where anthropogenic CO emissions are predominant (see Fig. 1a).…”

Global and regional evaluation of over-land spectral aerosol optical depth retrievals from SeaWiFS

“…The methodology adopted in this work draws from these studies. This evaluation is an important component in establishing the reliability of the satellite data for scientific use, such as in studies of air quality (Gupta and Christopher, 2008;Hoff and Christopher, 2009), radiative forcing (Chylek et al, 2003;Bellouin et al, 2005), trend detection (Zhang and Reid, 2010;Yoon et al, 2011), or visibility and aerosol forecasts (Zhang et al, 2008. The difficulty of accurate AOD retrieval over land has so far limited some of these applications (e.g., Li et al, 2009).…”

Different trends in extreme and median surface aerosol extinction coefficients over China inferred from quality-controlled visibility data

“…The variability and trends in China's air quality or aerosol properties have become the focus of numerous past studies (Jinhuan and Liquan, 2000;Che et al, 2007;Deng et al, 2008;Streets et al, 2008;Yoon et al, 2011;Guo et al, 2011;Zhang et al, 2015). While many of these works reached important conclusions about the temporal evolution of China's pollution, the majority only analyzed the arithmetic means (e.g., monthly or annual means of aerosol optical depth), with little attention paid to the extreme values.…”