# The Aerosol Radiative Effect on a Severe Haze Episode in the Yangtze River Delta

• Corresponding author: Hongnian LIU, liuhn@nju.edu.cn
• Funds:

Supported by the National Key Research and Development (973) Program (2014CB441203), National Natural Science Foundation of China (41575141 and 41305006), and Collaborative Innovation Center of Climate Change in Jiangsu Province

• doi: 10.1007/s13351-017-7007-4
• Due to increased aerosol emissions and unfavorable weather conditions, severe haze events have occurred frequently in China in the last 10 years. In addition, the interaction between the boundary layer and the aerosol radiative effect may be another important factor in haze formation. To better understand the effect of this interaction, the aerosol radiative effect on a severe haze episode that took place in December 2013 was investigated by using two WRF-Chem model simulations with different aerosol configurations. The results showed that the maximal reduction of regional average surface shortwave radiation, latent heat, and sensible heat during this event were 88, 12, and 37 W m–2, respectively. The planetary boundary layer height, daytime temperature, and wind speed dropped by 276 m, 1°C, and 0.33 m s–1, respectively. The ventilation coefficient dropped by 8%–24% for in the central and northwestern Yangtze River Delta (YRD). The upper level of the atmosphere was warmed and the lower level was cooled, which stabilized the stratification. In a word, the dispersion ability of the atmosphere was weakened due to the aerosol radiative feedback. Additional results showed that the PM2.5 concentration in the central and northwestern YRD increased by 6–18 μg m–3, which is less than 15% of the average PM2.5 concentration during the severely polluted period in this area. The vertical profile showed that the PM2.5 and PM10 concentrations increased below 950 hPa, with a maximum increase of 7 and 8 μg m–3, respectively. Concentrations reduced between 950 and 800 hPa, however, with a maximum reduction of 3.5 and 4.5 μg m–3, respectively. Generally, the aerosol radiative effect aggravated the level of pollution, but the effect was limited, and this haze event was mainly caused by the stagnant meteorological conditions. The interaction between the boundary layer and the aerosol radiative effect may have been less important than the large-scale static weather conditions for the formation of this haze episode.
• Fig. 1.  Simulated average surface PM2.5 concentration (μg m–3) during the severely polluted period.

Fig. 2.  Influence of the aerosol radiative effect on average meteorological factors (Case-2 minus Case-1): (a) downward shortwave radiation at the surface (W m–2); (b) upward sensible heat flux (W m–2); (c) latent heat flux (W m–2); (d) PBL height (m); (e) 2-m nighttime temperature (°C); (f) 2-m daytime temperature (°C); (g) 2-m relative humidity (%); and (h) 10-m wind speed (m s–1).

Fig. 3.  (a) PM2.5 concentration of Case-1. (b–d) Regional average variations (Case-2 minus Case-1) of meteorological factors caused by the aerosol radiative effect: (b) downward shortwave radiation and latent heat; (c) daytime 2-m temperature and sensible heat; (d) PBL height and 10-m wind speed. The land area to the north of 29.5°N in D03 was selected for the calculations.

Fig. 4.  Rate of change (i.e., $\frac{{{\rm{Case}}\text{-}2 - {\rm Case}\text{-}1}}{{{\rm{Case}}\text{-}1}} \times 100\%$) in the average ventilation coefficient (VC) during Phase 2 due to the aerosol radiative effect.

Fig. 5.  Average temperature profile with (dashed line) and without (solid line) the aerosol radiative effect in Nanjing.

Fig. 6.  Change (Case-2 minus Case-1) in the average PM2.5 concentration (μg m–3) caused by the aerosol radiative effect during Phase 2.

Fig. 7.  Changes in the average concentration (μg m–3) profiles at Nanjing due to the aerosol radiative effect: (a) PM2.5, (b) PM10, and (c) O3.

###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## The Aerosol Radiative Effect on a Severe Haze Episode in the Yangtze River Delta

###### Corresponding author: Hongnian LIU, liuhn@nju.edu.cn;
• 1. School of Atmospheric Sciences, Nanjing University, Nanjing 210023
• 2. Key Laboratory of Climate–Environment for East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
Funds: Supported by the National Key Research and Development (973) Program (2014CB441203), National Natural Science Foundation of China (41575141 and 41305006), and Collaborative Innovation Center of Climate Change in Jiangsu Province

Abstract: Due to increased aerosol emissions and unfavorable weather conditions, severe haze events have occurred frequently in China in the last 10 years. In addition, the interaction between the boundary layer and the aerosol radiative effect may be another important factor in haze formation. To better understand the effect of this interaction, the aerosol radiative effect on a severe haze episode that took place in December 2013 was investigated by using two WRF-Chem model simulations with different aerosol configurations. The results showed that the maximal reduction of regional average surface shortwave radiation, latent heat, and sensible heat during this event were 88, 12, and 37 W m–2, respectively. The planetary boundary layer height, daytime temperature, and wind speed dropped by 276 m, 1°C, and 0.33 m s–1, respectively. The ventilation coefficient dropped by 8%–24% for in the central and northwestern Yangtze River Delta (YRD). The upper level of the atmosphere was warmed and the lower level was cooled, which stabilized the stratification. In a word, the dispersion ability of the atmosphere was weakened due to the aerosol radiative feedback. Additional results showed that the PM2.5 concentration in the central and northwestern YRD increased by 6–18 μg m–3, which is less than 15% of the average PM2.5 concentration during the severely polluted period in this area. The vertical profile showed that the PM2.5 and PM10 concentrations increased below 950 hPa, with a maximum increase of 7 and 8 μg m–3, respectively. Concentrations reduced between 950 and 800 hPa, however, with a maximum reduction of 3.5 and 4.5 μg m–3, respectively. Generally, the aerosol radiative effect aggravated the level of pollution, but the effect was limited, and this haze event was mainly caused by the stagnant meteorological conditions. The interaction between the boundary layer and the aerosol radiative effect may have been less important than the large-scale static weather conditions for the formation of this haze episode.

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