Influence Of Haze Aerosol On Urban Heat Island Effect In Guanzhong Region

The haze aerosol is an important indicator to measure the quality of the air environment and one of the main factors affecting the climate.The variability of the regional aerosol’s spatial-temporal distribution and the uncertainty of the radiation effect have uncertain effects on the urban heat island（UHI）.This paper is based on day/night land surface temperature（LST）,aerosol optical depth（AOD）,aerosol fine mode fraction（FMF）,PM_2.5,PM₁₀,impervious surface percentage（ISP）,precipitation,air temperature and population density data,using the thermal field variability index and urban heat island footprint（UHI FP）to analyze the spatial feature of the UHI in the Guanzhong urban agglomeration.Using Getis-Ord Gi*index,the spatial differentiation of day/night LST and haze aerosols hot spot area in the urban heat island footprint was analyzed.Comprehensively using Mann-Kendall trend test,Hurst index,and STL time series analysis were used to research the time change trend of urban heat island intensity（UHII）and haze aerosol in Guanzhong urban agglomeration.Pearson correlation analysis,dominance analysis and attribution analysis were used to study the correlation between haze aerosol factors,meteorological factors,social factors and UHII,reveal the dominance degree of contribution of influencing factors to UHII,and quantify the contribution of haze aerosol to UHII.The main research results include:（1）Spatial variation of urban heat island and haze aerosol.The UHI FP of the Guanzhong urban agglomeration all expanded to varying degrees and had obvious seasonal differences.The day/night LST hotspots in the UHI FP accounted for a large proportion,and the areas of hotspots and sub-hotspots gradually increased.In the heat island footprint,the area of AOD hotspots in Xixian and Baoji was gradually decreasing,and the AOD hotspots in Tongchuan and Weinan were increasing.The area of FMF hotspots in Xixian,Tongchuan and Weinan was increasing,and the area of FMF hotspots in Baoji was decreasing.The areas of PM_2.5 and PM₁₀ hotspots in Baoji and Tongchuan were decreasing,while the hotspots in Xixian and Weinan were increasing with the expansion of the UHI FP.（2）Temporal trends of urban heat island intensity and haze aerosols.During the summer’s day in Xixian,Tongchuan and Weinan,the UHII increased significantly（P<0.05）.The trend of day/night SUHII in Xixian spring was significantly weakened（P<0.1）.The annual and spring and autumn UHII in Baoji during the daytime showed a significant upward trend（P<0.01）,and the autumn and winter UHII during nighttime showed a significant downward trend（P<0.01）.The overall trend of△AOD in Xixian and Baoji increased significantly（P<0.1）,and the urban aerosol concentration gradually increased.The change trend of△AOD between Tongchuan and Weinan was significantly different in the seasons.（3）Contribution analysis of haze aerosol and other factors to urban heat island intensity.During the day and night,△AOD was significantly negatively correlated with UHII（P<0.01）,and FMF,ISP,air temperature,and population density were significantly positively correlated with UHII（P<0.01）.In the dominance analysis,air temperature,ISP,△AOD,FMF were the most influential factors on day/night UHII,and△AOD,ISP and air temperature contributed more to nighttime UHII than daytime UHII.At night,the annual and seasonal△AOD was negatively correlated with UHII.When the aerosol concentration in urban area was lower than that in rural area,aerosol radiation effect had warming effect on urban heat island intensity.△AOD had the strongest effect on UHII at night with a value of 0.18℃ in winter.