Fast spreading of surface ozone in both temporal and spatial scale in Pearl River Delta

Surface ozone(O_(3))is a major air pollutant and draw increasing attention in the Pearl River Delta(PRD),China.Here,we characterize the spatial-temporal variability of ozone based on a dataset obtained from 57 national monitoring sites during 2013-2019.Our results show that:(1)the seasonal difference of ozone distribution in the inland and coastal areas was significant,which was largely affected by the wind pattern reversals related to the East Asian monsoon,and local ozone production and destruction;(2)the daily maximum 8hr average(MDA8 O_(3))showed an overall upward trend by 1.11 ppbv/year.While the trends in the nine cities varied differently by ranging from-0.12 to 2.51 ppbv/year.The hot spots of ozone were spreading to southwestern areas from the central areas since 2016.And ozone is becoming a year-round air pollution problem with the pollution season extending to winter and spring in PRD region.(3)at the central and southwestern PRD cities,the percentage of exceedance days from the continuous type(defined as≥3 days)was increasing.Furthermore,the ozone concentration of continuous type was much higher than that of scattered exceedance type(<3 days).In addition,although the occurrence of continuous type starts to decline since2017,the total number of exceedance days during the continuous type is increasing.These results indicate that it is more difficult to eliminate the continuous exceedance than the scatter pollution days and highlight the great challenge in mitigation of O_(3)pollution in these cities.

Evaluation of the Trend Uncertainty in Summer Ozone Valley over the Tibetan Plateau in Three Reanalysis Datasets

Trend uncertainty in the ozone valley over the Tibetan Plateau（OVTP）and the South Asian high（SAH）during1979–2009 in ERA-Interim（interim reanalysis data from the ECMWF）,JRA-55（55-yr reanalysis data from the Japan Meteorological Agency）,and NCEP-CFSR（Climate Forecast System Reanalysis）datasets was evaluated.The results showed that the NCEP-CFSR OVTP became strong in the summers of 1979–2009,whereas it became weak according to ERA-Interim and JRA-55.Satellite data merged with TOMS（Total Ozone Mapping Spectrometer）and OMI（Ozone Monitoring Instrument）agreed with the OVTP trend of NCEP-CFSR.The OVTP strengthening in NCEP-CFSR may have been caused by SAH intensification,a rising tropopause,and increasing ozone over non-TP（non-Tibetan Plateau）areas（27°–37°N,〈75°E and〉105°E）.Analogously,the OVTP weakening in ERA-Interim and JRA-55 may have been affected by weakening SAH,descending tropopause,and decreasing non-TP ozone.

Study on Ozone Change over the Tibetan Plateau

This paper reviewed the main results with respect to the discovery of low center of total column ozone （TCO） over the Tibetan Plateau （TP） in summer, and its formation mechanism. Some important advances are summarized as follows： The fact is discovered that there is a TCO low center over the TP in summer, and the features of the background circulation over the TP are analyzed; it is confirmed that the TP is a pathway of mass exchange between the troposphere and stratosphere, and it influences the TCO low center over the TP in summer; models reproduce the TCO low center over the TP in summer, and the formation mecbanism is explored; in addition, the analyses and diagnoses of the observation data indicate that not only there is the TCO low center over the TP in summer, but also TCO decrease trend over the TP is one of the strong centers of TCO decrease trend in the same latitude; finally, the model predicts the future TCO change over the TP.