Comment on acp-2021-918

doi:10.5194/acp-2021-918-rc1

Abstract

The canonical view of the northeast Asian anomalous anticyclone (NAAA) is a crucial factor for determining poor air quality in the North China Plain (NCP) on the interannual timescale. However, there is considerable intraseasonal variability in the NAAA in early winter (November to January), and the corresponding mechanism of its impacts on air pollution in the NCP is not well understood. Here, we find that the intraseasonal NAAA usually establishes quickly on day −3 with a life span of eight days, and its evolution is closely tied to the Rossby wave from upstream (i.e., the North Atlantic). Moreover, we find that the NAAA with a westward tilt might be mainly related to the wavenumbers 3−4. Further results reveal that under this background, the probability of regional air pollution for at least three days in the NCP is as high as 69 % (80 % at least two days) in NDJ period 2000−2021. In particular, air quality in the NCP tends to deteriorate on day 2 prior to the peak day of the NAAA and reaches a peak on day −1 with a life cycle of four days. In the course of air pollution, a shallower atmospheric boundary layer and stronger surface southerly wind anomaly associated with the NAAA in the NCP appear 1 day earlier than poor air quality, which provides dynamic and thermal conditions for the accumulation of pollutants and finally occurrence of the air pollution on the following day. Furthermore, we show that the stagnant air leading to poor air quality is determined by the special structure of temperature in the vertical direction of the NAAA, while weak ventilation conditions might be related to a rapid buildup of the NAAA. The present results quantify the impact of the NAAA on air pollution in the NCP on the intraseasonal timescale.

Highlights

The North China Plain (NCP, 32–42oN, 110–120oE) has undergone a series of air pollution episodes, in late autumn and early winter (Wang et al, 2019; Yin et al, 2021), which is recognized as significant human health risk and economic activity (Geng et al, 2021a)
We find that the intraseasonal northeast Asian anomalous anticyclone (NAAA) usually establishes quickly on day −3 with a life span of eight days, and its evolution is closely tied to the Rossby wave from upstream
We show that the stagnant air leading to poor 25 air quality is determined by the special structure of temperature in the vertical direction of the NAAA, while weak ventilation conditions might be related to a rapid buildup of the NAAA

Summary

Introduction

The North China Plain (NCP, 32–42oN, 110–120oE) has undergone a series of air pollution episodes, in late autumn and early winter (Wang et al, 2019; Yin et al, 2021), which is recognized as significant human health risk and economic activity (Geng et al, 2021a). Specific to air pollution in the NCP, previous studies have found many influence factors, including sea surface temperature 40 (Chang et al, 2016; Jeong et al, 2018; Yu et al, 2020), Arctic sea-ice (Wang et al, 2015, Zou et al, 2020), Eurasian snow cover and soil (Zou et al, 2017; Yin et al, 2018) and climate internal variability including the Eurasian Teleconnection (Li et al, 2019) and subtropical westerly jet waveguide (An et al, 2020, 2021; Mei et al, 2021), and so on. The NAAA leads to higher temperature over East Asia by weakening East Asian trough (Song et al, 2016), and directly modulating stagnant and ventilated conditions for air pollution in the NCP (e.g., Chang et al, 2016; Zhong et al, 2019). The NAAA can’t be ignored when studying 50 meteorological causes of air pollution in the NCP

Methods

Results

Conclusion