This study investigated the impact of gaseous precursor emission reduction over key source regions on inorganic aerosols(IAs)and PM2.5 in Tianjin during a typical regional haze process with the NAQPMS(Nested Air Quality Prediction Modeling System).Based on high-precision simulations,the high IA concentration originating from the North China Plain(NCP)was transported to East China and subsequently returned to the NCP region in a clockwise pattern,resulting in two pollution periods in Tianjin.The online pollutant source-tagging method coupled with the NAQPMS was used to quantify the contribution of different source regions to IAs in Tianjin,and the NCP region was identified as the key source area,with a daily contribution of 57.6%-100%.Sensitivity experiments were performed to analyze the impact of reducing precursor emissions by 30%in the NCP region a day before a pollution event and during the pollution days in Tianjin.NH3 control notably reduced IA and PM2.5 concentrations in Tianjin by 30.8%and 13.3%,respectively,which were 16 and 26.6 times that of SO2 reduction and 7 and 6.4 times that of NOx reduction,respectively.SO2 reduction increased nitrate concentration by 3.5%in Tianjin because SO2 control increased gaseous NH3,and excessive NH3 in the atmosphere can neutralize HNO3 to nitrate production based on the thermodynamic effect.NOx reduction exhibited positive and negative effects on nitrate in different areas of the NCP,and transport of the two effects occurring in upstream areas caused the concentrations of nitrate,IAs,and PM2.5 in Tianjin to decrease first and then increase.This study highlights that transporting positive effects in key source areas can contribute to PM2.5 reduction while transporting negative effects harms the joint prevention and control of air pollution.
Hazardous/lethal compound temperature-humidity heatwaves with a wet bulb temperature(i.e.,≥33℃/35℃)can severely affect human health.The middle and lower reaches of the Yangtze River always experience high-frequency compound temperature-humidity heatwaves.This study investigates the population exposed to these heatwaves in the middle and lower reaches of the Yangtze River for the near-term(2021-2040),medium-term(2041-2060),and long-term(2081-2100)periods using the five-climate model outputs under seven SSPs(Shared Socioeconomic Pathways)—based scenarios(i.e.,SSP1-1.9,SSP1-2.6,SSP4-3.4,SSP2-4.5,SSP4-6.0,SSP3-7.0,and SSP5-8.5).These scenarios are obtained from the CMIP6(Coupled Model Intercomparison Project phase 6)in combination with the demographic characteristics under the Shared Socioeconomic Pathways(i.e.,SSP1-5).The results show that during the baseline period of 1995-2014,hazardous/lethal compound temperature-humidity heatwaves occurred at frequencies of approximately 6 d and 3 d in the middle and lower reaches of the Yangtze River,where the longest duration was approximately 10 d and 4 d,respectively.In the future,the frequency and duration of such heatwaves are projected to increase in the long-term period,where the frequency is expected to be approximately 12-39 d and 7-24 d,and the longest duration is as long as 30 d and 14 d,respectively.In the baseline period,the hazardous/lethal compound temperature-humidity heatwaves affected an area of approximately 74.8×104 and 22.3×104 km2 in the middle and lower reaches of the Yangtze River,exposing the populations of 170 million and 20 million people of the hazardous/lethal compound temperature-humidity heatwaves,respectively.The impact range and maximum exposed population in the 21st century were observed in the long-term period,accounting for approximately 83%-100%and 32%-98%of the study area,respectively.The exposed population was approximately 1.2-2.5 and 2.5-20.5 times higher than that during the base period in the middle and lower reaches of the Yangtze River,respectively.The population exposed to the lethal compound temperature-humidity heatwaves increased considerably by approximately 40 million-370 million.Spatially,the main areas affected by these heatwaves in the 21st century are Shanghai,northern Zhejiang,southern Jiangsu,southern Anhui,eastern Hunan,and eastern Jiangxi.Overall,forecasting,early warning,and risk prevention of lethal compound temperature-humidity heatwaves must be urgently improved.
Through the measurement results of the Beijing Nanjiao radiosonde in January-October 2021 and measurement data of the automatic station of the Alpine Skiing Venue in Yanqing during the Winter Olympic Games,the accuracies of temperature and humidity profiles retrieved by a ground-based MicroWave Radiometer(MWR)were assessed.The results revealed that the MWR-retrieved temperature profile exhibited a good correlation with the observations from the radiosonde and the automatic station,with relatively small errors and good reliability.However,the MWR-retrieved humidity profile exhibited poor correlation with the observations from the radiosonde and the automatic station(correlation coefficient=0.81).Comparison of the results from the MWR and those of different automatic stations and the radiosonde revealed that at levels of 0.15-0.6 km,the MWR-retrieved temperature profile exhibited a good correlation with the observations from the radiosonde and the automatic station.Furthermore,the Root-Mean-Square Error(RMSE)and Average Deviation(AD)of the MWR-retrieved temperature profile concerning the observation from the automatic station increased with increasing height and nevertheless those of the MWR-retrieved temperature profile with respect to the observation from the radiosonde decreased with increasing height at levels of 0.15-0.6 km.The correlation,RMSE,and AD of the MWR-retrieved relative humidity profile with respect to the observation from the radiosonde and the automatic station increased with increasing height.Based on the comparison between the MWR and the radiosonde,the authors observed a significant positive correlation between the MWR-retrieved temperature and radiosonde observations over the entire sounding height,which is higher in the lower atmosphere than in the upper atmosphere.In contrast,the correlation of the MWR-retrieved humidity profile with the observation from the radiosonde was significantly lower than that of the temperature profile and exhibited a negative correlation at levels of 2.75-3.5 km.The Mean Error(ME)of the MWR-retrieved temperature profile at each sounding height,except at 10 km,was within 2℃.Meanwhile,the RMSE and AD of the MWR-retrieved temperature profile were about 3.4℃ and 2.5℃,respectively,at levels of＜3 km.Furthermore,the RMSE and AD values of all other levels increased with increasing height.The RMSE and AD of the MWR-retrieved humidity profile were expectedly higher than those of the temperature profile at all levels.Meanwhile,the ME of the MWR-retrieved humidity profile was large at most levels,with a maximum of 23.67%.Precipitation caused the error in the MWR-retrieved temperature profile to increase at the most levels for the duration of 0800 LST and 2000 LST,in which the RMSE and AD under precipitation were expectedly higher than those under the no-rain condition at levels＞0.5 km.However,the RMSE and AD of the MWR-retrieved humidity profile during 0800 LST and 2000 LST in rainy days(at most levels in the lower atmosphere)were expectedly lower than those during clear days,in which the RMSE and AD at 2000 LST degraded dramatically.
Based on the snow depth dataset over China and CN05-gridded precipitation data over China,the relationship between the snow depth in the Tibetan Plateau(TP)and summer precipitation in Yunnan is investigated through singular vector decomposition and correlation analysis.Results show that the positive snow depth anomalies in the central and western TP during winter and spring can enhance the summer precipitation in Yunnan,particularly in the Jinsha River basin and the southwest of Yunnan,and the correlations between the snow depth in the TP and the summer precipitation in Yunnan may be independent of the influence of the El Niño-Southern Oscillation.The possible impact mechanism has been investigated through diagnostic analyses using the fifth generation ECMWF reanalysis datasets(ERA5).The extreme snow depth in the key region of the TP leads to a low surface air temperature in the central and western parts of the TP and nearby areas in spring.This is conducive to the late onset of the South Asian summer monsoon and leads to a weak South Asian summer monsoon and the associated monsoon depression,along with the abnormal westerly wind to the south of the TP.Moreover,the cold surface temperature associated with the extreme snow depth in the TP can initiate the wave train at 200 hPa,which propagates from the western part of the TP through Mongolia to Northeast Asia along the westerly jet stream.Furthermore,an anomalous cyclonic circulation can be observed in Northeast Asia,which is conducive to the southward movement of cold air in the middle and high latitudes,leading to increased rainfall in Yunnan.Meanwhile,a wave train at 850 hPa,which spreads from the southwest side of the plateau to the South China Sea,can be observed,leading to an anomalous anticyclonic circulation in the South China Sea.An anomalous low-level shear over Yunnan develops due to the westerly wind on the southern side of the plateau and the southwesterly wind on the northwest side of the anticyclonic circulation in the South China Sea,which is favorable for increased precipitation in Yunnan.Meanwhile,cold air flows southward to Yunnan and converges with warm and humid air,which also contributes to the increased summer precipitation in Yunnan.
Based on the use of multiple linear regression models,the air quality of Jiyuan City,a typical industrial city,was analyzed at different stages from October 2021 to March 2022.The impact characteristics of the change of meteorological factors on PM2.5,PM2.5 pollution level,and the difference in the growth rate of pollutant concentration before and after the start of winter heating(15 Nov 2021)were studied to explore the characteristics of PM2.5 pollution in cities along Taihang Mountain in autumn and winter.Results reveal that in the first stage(1 Oct-14 Nov 2021),26.1%of PM2.5 hourly concentration change was determined using meteorological factors,and the correlation between any single factor and PM2.5 was＜36%.In the second stage(15 Nov-31 Dec 2021),72.4%of the hourly concentration change of PM2.5 was determined using meteorological factors.Wind direction,relative humidity,and visibility had considerable influences on PM2.5,and the correlation between PM2.5 and relative humidity and visibility was the highest(61.5%correlation with relative humidity and 73.1%correlation with visibility).In the third stage(1-31 Jan 2022),53.2%of hourly concentration change of PM2.5 was determined using meteorological factors,and the relative humidity and wind speed had no considerable effect on the hourly change of PM2.5,which is associated with the considerable effect of long-range migration and detention of pollution clusters in this stage.In the fourth stage(1 Feb-31 Mar 2022),32.2%of PM2.5 hourly concentration change was determined using meteorological factors.Wind speed had no considerable effect on PM2.5 hourly change because it was affected by sand and dust.During the pollution period in autumn and winter in Jiyuan City,the main components of particulate matter were NO3-,NH4+,OC,and SO42-,with the proportion of secondary inorganic ions(SO42-,NO3-,and NH4+)being＞65.7%,and the secondary pollution was severe.Thus,the growth rates of particle component concentrations show that,with the increase in pollution,the growth rates of NO3-,S,EC,and Cl-decrease while those of SO42-,OC,K+,and NH4+ exhibit a"slow-fast"trend.
