Trends and Variability in Aerosol Optical Depth over North China from MODIS C6 Aerosol Products during 2001–2016

Abstract

This study analyzed the variability and trend in aerosol optical depth (AOD) over North China using the latest MODIS/Terra C6 merged Dark Target/Deep Blue AOD monthly data at 550 nm from 2001 to 2016. The spatial distribution of the annual mean AOD was generally characterized by two prominent high-value centers located in the industrially and economically developed areas of the North China Plain and East China, and the dust aerosol-dominated areas of southern Xinjiang. The seasonally averaged AOD reached its maximum in spring (0.430 ± 0.049), followed by summer (0.356 ± 0.035) and winter (0.282 ± 0.039), with the minimum occurring in autumn (0.219 ± 0.022). There were notable long-term annual trends in AOD in different regions over North China during 2001-2016: a decreasing AOD trend was found in Qinghai Tibet (−0.015 ± 0.010/decade), Northwest China (−0.059 ± 0.013/decade at 99% confidence level), and the North China Plain (−0.007 ± 0.021/decade), but a positive increasing trend was identified in northern Xinjiang (0.01 ± 0.006/decade), southern Xinjiang (0.002 ± 0.013/decade), East China (0.053 ± 0.042/decade), and Northeast China (0.016 ± 0.029/decade). Seasonal patterns in the AOD regional long-term trend were evident. The AODs in spring over all the study regions, except East China, exhibited a decreasing trend, with the maximum trend value observed in Northwest China (−0.099 ± 0.029/decade at 99% confidence level); whereas AODs in autumn, except in Northwest China, showed an increasing trend, with the maximum trend value occurring in East China (0.073 ± 0.038/decade). Geographically, we also examined the annual and seasonal spatial patterns of AOD trends over North China. The annual spatial trends in AOD revealed a dominance of positive trends in most regions over the whole of North China from 2001 to 2016, but especially in East and Northeast China (AOD trend value of about 0.16/decade); whereas a negative trend was observed over northern Inner Mongolia (AOD trend value of about −0.12/decade). In addition, seasonal spatial trend analyses indicated that a continual clear upward trend occurred in East China in the autumn and winter seasons during the study period, with the maximum average increase occurring in winter (about 0.20/decade).

Spatial and seasonal variations of aerosols over China from two decades of multi-satellite observations – Part 1: ATSR (1995–2011) and MODIS C6.1 (2000–2017)

“…Obviously, other choices are possible, such as those made by Luo et al (2014) or Wang et al (2017). The regions selected by Luo et al (2014) are generally somewhat smaller than those in Fig.…”

“…Regions were also chosen to represent the Tibetan Plateau and Taklamakan Desert. Wang et al (2017) selected seven regions in North China (north of 32 • N), some of which partly overlap with the regions selected for the current study. Other studies on the seasonal variation over China were guided by the location of observational sites (e.g., Che et al, 2015;Wang et al, 2015).…”

“…The concentrations of aerosols in China have been relatively high over the last two decades (e.g., Wang et al, 2017;Zhang et al, 2017), and are rising as a consequence of economic development, industrialization, urbanization and the associated transport and traffic. Examples of other factors affecting interannual and seasonal variations of the aerosol optical depth (AOD) over China are the generation and transport of desert dust (e.g., Proestakis et al, 2018;Wang et al, 2008), seasonal biomass burning (e.g., Chen et al, 2017a) and meteorological conditions and large-scale circulation (Zhu et al, 2012).…”

Spatial and seasonal variations of aerosols over China from two decades of multi-satellite observations. Part I: ATSR (1995–2011) and MODIS C6.1 (2000–2017)

“…Also regions were chosen to represent the Tibetan Plateau and Taklamakan desert. Wang et al (2017) o N) some of which partly overlap with the regions selected for the current study. Other studies on the seasonal variation over China were guided by the location of observational sites (e.g.…”

“…Such considerations resulted in the selection of 10 study areas as shown in Fig. 2: seven of them (regions 1-7) in SE China, one covering the Tibetan Plateau (region 8), one over the Taklamakan desert (region 9) and one over northeastern (NE) China (region 10 Obviously, other choices are possible, such as those made by Luo et al (2014) or Wang et al (2017). The regions selected by Luo et al (2014) are overall 15 somewhat smaller than those in Fig.…”