The spatio-temporal characteristics of aerosol optical thickness as well as the relationship with PM_2.5 in Xiamen city, China

Long-term aerosol optical thickness (AOT) composited data (2002–2017) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua spacecraft was used to evaluate the temporal and spatial variability of aerosol in Xiamen city by using wavelet analysis, and the relationship between the surface mass concentrations of particulate matter with aerodynamic diameters less than 2.5 μm (PM_2.5) and the AOT was analyzed by using linear regression. The results showed that AOT increased gradually from 2002 to 2011, and then decreased. AOT displayed a significant 9-month periodicity in AOT was inferred wavelet analysis. AOT also showed significant annual variability in response to changes in weather and aerosol pollution. We observed highest AOT values in April, with a monthly mean of 1.00 ± 0.18. Lowest values were observed in December, with a mean AOT of 0.52 ± 0.11. Multi-year monthly AOT fluctuations were lowest in January with a low variation coefficient (0.14), and the largest fluctuations appeared in July with a high variation coefficient (0.29). Higher AOT values (~ 1.1) were predominantly located in the southern urban areas of Xiamen and lower AOT values (~ 0.3) were mainly located in northern rural regions. The aerosol pollution was serious in April with the smallest spatial variation coefficient of 0.25, and the highest spatial variation coefficient appeared in July. Highest intraannual variability predominantly occurred in the high-value areas in the center of Xiamen. AOT values remained high in Xiamen Island throughout the year with a multi-year mean of 0.87. There was a moderate correlation between ground-based PM_2.5 and MODIS AOT. Therefore, we confirm the suitability of MODIS AOT to accurately estimate PM_2.5 concentration and evaluate the temporal and spatial characteristics of air quality in Xiamen.