Observed Relationships Between the Urban Heat Island, Urban Pollution Island, and Downward Longwave Radiation in the Beijing Area

Abstract

We used the mean air temperature and particulate matter concentration at northern and southern rural stations as rural background values to calculate the urban heat island intensity (UHII) and urban pollution island intensity (UPII) for Beijing. The correlation between UHII and UPII is significantly negative in winter during the daytime and nighttime when selecting southern rural background stations but significantly positive in spring during both daytime and nighttime and in winter during the nighttime when selecting northern rural background stations. The downward longwave radiation (DLR) is highly correlated with surface air temperature and water vapor, and with particulate matter concentration in winter and summer. Water vapor also has a high correlation with particulate matter concentration in winter and summer. Winter data were used to investigate the particulate matter contribution to DLR to minimize the effect of humidity. The results indicate that in winter the urban area DLR and net radiation increased more than rural area under polluted conditions compared with clean conditions, which may lead to an increase in UHII. But in other seasons with more moisture, the aerosol effect on DLR is smaller than water vapor. Our results imply that the contribution of air pollutants to DLR had been overestimated in recent studies without removing water vapor effects on the longwave radiation. We suggest that the interaction between the urban heat island and the urban pollution island and related mitigation strategies needs to be carefully studied in the future by considering different climate zone and seasons.On the other hand, a UPI can increase aerosol radiative forcing in an urban area. The downward longwave radiation (DLR) was found to be greater at urban sites, which have more polluted air (

The spatiotemporal heterogeneity of the relationship between PM2.5 concentrations and the surface urban heat island effect in Beijing, China

“…Many studies have demonstrated a strong interaction between air pollution and the UHI effect, which shows that there is a strong correlation between them. Studies have shown that under pollution conditions, the net radiation and downward longwave radiation are higher in urban areas than in rural areas in winter, which leads to an increase in UHI intensity (Li et al, 2020). The urban temperature rise brought by the UHI effect can catalyze atmospheric photochemical reactions, which are conducive to the generation of secondary pollution of PM 2.5 .…”

“…Previous studies have selected rural meteorological stations in heavily polluted areas in the south and rural meteorological stations in less polluted areas in the north of Beijing to study the interaction between UHIs and air pollution and obtained completely opposite results (Li et al, 2020). The correlation between UHI intensity and urban pollution island intensity is significantly negative when choosing the southern rural meteorological station but positive when choosing the northern rural meteorological station.…”

“…The simulation results of the Weather Research and Forecasting (WRF) model coupled with Chemistry model show that UHI intensity will increase on polluted days in winter (Chen et al, 2018), which is consistent with the result of Li et al (2007) that the frequently polluted urban center area is highly coincident with the UHI center. However, by selecting two rural background stations with different pollution levels in northern and southern Beijing to analyze the interaction between pollutants and the UHI, two completely opposite results were obtained (Li et al, 2020). Xu et al (2013) also pointed out that the interaction between them has the characteristics of seasonal and regional dependence.…”

“…Green space planning can be used to control the existence of atmospheric particulate matter and the UHI effect (Xu et al, 2013). The influence of water vapor on downward longwave radiation also raises the question of the accuracy of previous research on the relationship between UHIs and air pollution (Li et al, 2020). Therefore, the normalized difference vegetation index (NDVI) and modified normalized difference water index (MNDWI) were chosen to represent the distribution of vegetation and water bodies, respectively, as two indices to distinguish biophysical gradients.…”

Synergy between the Urban Heat Island and the Urban Pollution Island in Mexico City during the Dry Season

“…Most of the studies reviewed are from cities in Europe, The United States of America and Asia (Ulpiani, 2021). Recently, three studies focus on the relation UPI and UHI in Berlin (Li et al, 2018), Beijing (Li et al, 2020), and Seoul (Ngarambe et al, 2021). During the summer in Berlin, a positive correlation has been found between the spatial distributions of the UPI defined from ground-based pollution data and the UHI measured with Land Surface Temperature from satellites.…”