Superimposed effects of typical local circulations driven by mountainous topography and aerosol-radiation interaction on heavy haze in the Beijing-Tianjin-Hebei central and southern plains in winter
Abstract. Although China’s air quality has substantially improved in recent years due to the vigorous emission reduction, the Beijing-Tianjin-Hebei (BTH) region, especially its central and southern plains at the eastern foot of the Taihang Mountains, has been the most polluted area in China with persistent and severe haze in winter. Combining meteorology-chemistry coupled model simulations and multiple observations, this study explored the causes of several heavy haze events in this area in January 2017, focusing on local circulations related to mountain terrain. The study results showed that on weather scale, the configuration of the upper, middle, and lower atmosphere provided favorable weather and water vapor transport conditions for the development of haze pollution. Under the weak weather-scale systems, local circulation played a dominant role in the regional distribution and extreme values of PM2.5. Influenced by the Taihang and Yanshan Mountains, vertical circulations and wind convergence zone were formed between the plain and mountain slopes. The vertical distribution of pollutants strongly depended on the intensity and location of the circulation. Strong and low circulation was more unfavorable to the vertical diffusion and horizontal transport of near-surface pollutants. More importantly, we found that aerosol-radiation interaction (ARI) significantly amplified the impacts of local vertical circulations on heavy haze by two mechanisms. First, ARI strengthened the vertical circulations at the lower levels, with the zonal wind speeds increasing by 0.2–0.8 m s-1. Meanwhile, ARI could cause a substantial downward shift of the vertical circulations (~100 m). Second, ARI weakened the horizontal transport of pollutants by reducing the westerly winds below 300 m and enhancing the wind convergence below 1000 m. Under these two mechanisms, pollutants could only recirculate in a limited space. This superposition of typical local circulation and ARI eventually contributed to the accumulation of pollutants and the consequent deterioration of haze pollution in the region.
Yue Peng et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2022-780', I. Pérez, 03 Jan 2023
- AC2: 'Reply on RC1', Yue Peng, 09 Mar 2023
RC2: 'Comment on egusphere-2022-780', Anonymous Referee #2, 03 Jan 2023
- AC1: 'Reply on RC2', Yue Peng, 09 Mar 2023
Yue Peng et al.
Yue Peng et al.
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The current paper is focused on the air pollution by PM2.5 at the Beijing-Tianjin-Hebei region in China. The subject merits to be investigated due to the noticeable impact on the affected population. The period investigated is around January 2017, although only three days are selected. Measurements are considered together with modelling analysis. Observations are provided by the National Environmental Monitoring Center, 149 stations, and the Hebei Meteorological service, 210 stations. Moreover, two kind of modelling calculations are used, one of them with the aerosol-radiation interaction, and the second calculation without this interaction. The synoptic pattern is presented at varied pressure surfaces, and vertical cross-sections with the airflow and concentration are also shown. Although the subject and procedure are suitable for a publication, some restrictions of this research indicate that this paper could be accepted in a journal with low impact, but not in Atmospheric Chemistry and Physics.
The main inconvenience lies on the extremely low number of situations where the study is made, only three days, 6th, 17th, and 24th. Although the analysis is detailed, the readers should know if these days are representative enough for the pollution days at this site. Moreover, the readers should know if these conditions could be reproduced at different sites.
Since the pollution levels are affected by factors such as the emissions and the meteorological variables, some information about the patterns of both factors could be useful to focus the pollution problem at the site.
Figure 2 presents the concentration evolution. The authors should comment the reason to discard the first days of the month when the concentrations are even higher than those selected for the analysis.
Some statistics to contrast the measured and calculated concentrations should be introduced. If the correlation is made with the Pearson correlation coefficient, the authors should consider that a good value of this estimator could not indicate a good agreement between measured and calculated values. A better statistic for this calculation could be the index of agreement.
The names of mountain ranges and sea should be introduced in Fig. 1a (indicated in the text, l. 51), not in Fig. 1b.