Hao Wu1,2, Tijian Wang 2, Qin’geng Wang 1, Nicole Riemer3, Yang Cao4, Chong Liu2, Chaoqun Ma2, Xiaodong Xie2


School of Environment, Nanjing University, Nanjing 210023, China
School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China
Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Jiangsu Urban Planning and Design Institute, Nanjing 210024, China


Received: February 28, 2019 | Revised: September 19, 2019 | Accepted: October 15, 2019

Download Citation: ||https://doi.org/10.4209/aaqr.2019.02.0100 |


Highlights

  • PM2.5 levels of mega cities in YRD were reduced by 29.41%–48.36%.
  • The UHI intensity was impacted by up to 1 K during the day and night.
  • PM2.5 caused the change of UHI intensity by affecting radiation.

ABSTRACT

The National Air Pollution Control Plan implemented by China in 2013 reduced the concentrations of air pollutants, especially PM2.5 (aerosol particles with an aerodynamic diameter equal to or less than 2.5 µm), between 2014 and 2017. This reduction in PM2.5 potentially affected the intensity of urban heat islands (UHIs), as the presence of fine particles can influence the energy balance of the earth-atmosphere system. In this study, the effect of the pollution control plan on the UHI intensity in the Yangtze River Delta, China, was investigated via observational analysis and numerical modeling. According to the observational data, the PM2.5 concentrations in the megacities of the Yangtze River Delta, viz., Shanghai, Nanjing, Hangzhou and Hefei, in 2017 were ~35 µg m–3, showing decreases of approximately 48.36%, 28.25%, 29.41% and 32.5%, respectively, compared to 2014. Furthermore, these reductions in the PM2.5 concentration correlated well with the strengthened diurnal intensity (increasing by up to 1 K) and the weakened nocturnal intensity (decreasing by up to 1 K) of the UHIs. Numerical simulations confirmed that this “seesaw effect” on the UHI intensity was due to the decrease in PM2.5 and the consequent increase in the downward surface shortwave radiation and the outgoing top-of-the-atmosphere longwave radiation. Thus, the Air Pollution Control Plan noticeably affected the UHI intensity by reducing PM2.5—a factor which should be considered in future studies on urban climate and environmental planning.

Keywords: PM2.5; Urban heat island; WRF-Chem; Yangtze River Delta.


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