scholarly journals Ozone variability induced by synoptic weather patterns in warm seasons of 2014–2018 over the Yangtze River Delta region, China

2021 ◽  
Vol 21 (8) ◽  
pp. 5847-5864
Author(s):  
Da Gao ◽  
Min Xie ◽  
Jane Liu ◽  
Tijian Wang ◽  
Chaoqun Ma ◽  
...  
Keyword(s):  
Time Series ◽  
North China ◽  
Meteorological Factors ◽  
Yangtze River Delta ◽  
Aleutian Low ◽  
Weather Patterns ◽  
The North ◽  
Synoptic Weather ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Ozone (O3) pollution is of great concern in the Yangtze River Delta (YRD) region of China, and the regional O3 pollution is closely associated with dominant weather systems. With a focus on the warm seasons (April–September) from 2014 to 2018, we quantitatively analyze the characteristics of O3 variations over the YRD, the impacts of large-scale and synoptic-scale circulations on the O3 variations and the associated meteorological controlling factors, based on observed ground-level O3 and meteorological data. Our analysis suggests an increasing trend of the regional mean O3 concentration in the YRD at 1.8 ppb per year over 2014–2018. Spatially, the empirical orthogonal function analysis suggests the dominant mode accounting for 65.7 % variation in O3, implying that an increase in O3 is the dominant tendency in the entire YRD region. Meteorology is estimated to increase the regional mean O3 concentration by 3.1 ppb at most from 2014 to 2018. In particular, relative humidity (RH) plays the most important role in modulating the inter-annual O3 variation, followed by solar radiation (SR) and low cloud cover (LCC). As atmospheric circulations can affect local meteorological factors and O3 levels, we identify five dominant synoptic weather patterns (SWPs) in the warm seasons in the YRD using the t-mode principal component analysis classification. The typical weather systems of SWPs include the western Pacific Subtropical High (WPSH) under SWP1, a continental high and the Aleutian low under SWP2, an extratropical cyclone under SWP3, a southern low pressure and WPSH under SWP4 and the north China anticyclone under SWP5. The variations of the five SWPs are all favorable to the increase in O3 concentrations over 2014–2018. However, crucial meteorological factors leading to increases in O3 concentrations are different under different SWPs. These factors are identified as significant decreases in RH and increases in SR under SWP1, 4 and 5, significant decreases in RH, increases in SR and air temperature (T2) under SWP2 and significant decreases in RH under SWP3. Under SWP1, 4 and 5, significant decreases in RH and increases in SR are predominantly caused by the WPSH weakening under SWP1, the southern low pressure weakening under SWP4 and the north China anticyclone weakening under SWP5. Under SWP2, significant decreases in RH, increases in SR and T2 are mainly produced by the Aleutian low extending southward and a continental high weakening. Under SWP3, significant decreases in RH are mainly induced by an extratropical cyclone strengthening. These changes in atmospheric circulations prevent the water vapor in the southern and northern sea from being transported to the YRD and result in RH significantly decreasing under each SWP. In addition, strengthened descending motions (behind the strengthening trough and in front of the strengthening ridge) lead to decreases in LCC and significant increases in SR under SWP1, 2, 4 and 5. The significant increases in T2 would be due to weakening cold flow introduced by a weakening continental high. Most importantly, the changes in the SWP intensity can make large variations in meteorological factors and contribute more to the O3 inter-annual variation than the changes in the SWP frequency. Finally, we reconstruct an empirical orthogonal function (EOF) mode 1 time series that is highly correlated with the original O3 time series, and the reconstructed time series performs well in defining the change in SWP intensity according to the unique feature under each of the SWPs.

scholarly journals Dynamic Processes Dominating Ozone Variability in Warm Seasons of 2014–2018 over the Yangtze River Delta Region, China

2020 ◽  
Author(s):  
Da Gao ◽  
Min Xie ◽  
Jane Liu ◽  
Tijian Wang ◽  
Chaoqun Ma ◽  
...  
Keyword(s):  
Time Series ◽  
Yangtze River ◽  
North China ◽  
Western Pacific Subtropical High ◽  
Yangtze River Delta ◽  
Western Pacific ◽  
The Yangtze River ◽  
The North ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Ozone (O3) pollution is of great concern in the Yangtze River Delta (YRD) region of China, and the regional O3 pollution is closely associated with dominant weather systems. With a focus on the warm seasons (April–September) from 2014 to 2018, we quantitatively analyze the characteristics of O3 variations over the YRD, the impacts of large-scale and synoptic-scale circulations on the variations and the associated meteorological controlling factors, based on observed ground-level O3 and meteorological data. Our analysis suggests an increasing trend of the regional mean O3 concentration in the YRD at 1.81 ppb per year over 2014–2018. Spatially, the empirical orthogonal function (EOF) analysis suggests the dominant mode accounting for 65.70 % variation in O3, implying that an increase in O3 is the dominant tendency in the entire YRD. Meteorology is estimated to increase the regional mean O3 concentration by 2.81 ppb at most from 2014 to 2018. Relative humidity is found to be the most influential meteorological factor impacting O3 concentration. As the atmospheric circulation can affect local meteorological factors and O3 levels, we identify five dominant synoptic weather patterns (SWPs) in the warm seasons in the YRD using the t-mode principal component analysis (PTT) classification. The typical weather systems of SWPs include western Pacific Subtropical High (WPSH) under SWP1, a continental high under SWP2, an extratropical cyclone under SWP3, a southern low pressure and WPSH under SWP4 and the north China anticyclone under SWP5. The annual variations of all five SWPs are favorable to the increase in O3 concentrations over 2014–2018. Moreover, the change in SWP intensity contributes more to the O3 inter-annual variation than the SWP frequency change. The SWP intensity change includes the weakening and northward-extending of the western Pacific subtropical high (WPSH) under SWP1, the weakening of the continental high under SWP2, an extratropical cyclone strengthening under SWP3, the southern low pressure weakening and WPSH weakening under SWP4, and the north China anticyclone weakening under SWP5. All these changes prevent the water vapor in the southern sea from being transported to the YRD, and increase air temperature in the YRD. In addition, the descending motions strengthen in the YRD located behind the trough and in front of the ridge due to the strengthening of the ridge and trough in the westerlies. Then, the strengthened descending motion leads to less cloud cover and strong solar radiation, which are favorable to O3 formation and accumulation. Finally, we reconstruct an EOF mode 1 time series that shows high correlation with the original O3 time series, and the reconstructed time series performs well in defining the change in SWP intensity according to the unique feature under each of the SWPs.

scholarly journals Modeling the Effects of Climate Change on Surface Ozone during Summer in the Yangtze River Delta Region, China

2019 ◽  
Vol 16 (9) ◽  
pp. 1528 ◽  
Author(s):  
Da Gao ◽  
Min Xie ◽  
Xing Chen ◽  
Tijian Wang ◽  
Chenchao Zhan ◽  
...  
Keyword(s):  
Yangtze River ◽  
Meteorological Factors ◽  
Yangtze River Delta ◽  
The Yangtze River ◽  
The South ◽  
Southerly Wind ◽  
The North ◽  
The Yrd ◽  
Surface O3 ◽  
The Yangtze River Delta

Future climate change can impact ozone concentrations by changing regional meteorological factors related to ozone (O3) pollution. To better understand the variations of meteorological factors and their effects on O3 formation processes under future climate conditions, we model the present and the future meteorology and air quality in summer over the Yangtze River Delta (YRD) region by using the Weather Research and Forecasting Model with Chemistry module (WRF/Chem), which is driven by the outputs of Community Climate System Model version 4 (CCSM4). The simulations predict that solar radiation, 2-m air temperature, and wind speed increase in the daytime over most of the YRD region. Absolute humidity and precipitation increase in the north and decrease in the south, while the planetary boundary layer height (PBLH) has an opposite change pattern displaying a decrease in the north and an increase in the south. The southerly wind will be strengthened in the daytime. At night, the change patterns of the meteorological factors are similar to the daytime but with small variations. Meanwhile, O3 and its precursors all increase in the north and decrease in the south. The increases of NOx, volatile organic compounds (VOC), and CO are related with the decreases of PBLH and the input effect of stronger southerly wind, while the decreases are attributed to the output effect of the stronger southerly wind. During the daytime, the increase of surface O3 in the north is dominated by the chemical processes related with the increases of solar radiation, air temperature, and O3 precursors. The decrease of surface O3 in the south is mainly caused by the transport process changing with the strengthened southerly wind. At night, the surface O3 changing the amplitude is less than the daytime. The less O3 variations at night can be attributed to an O3 titration reaction with NO, the changes in NOx concentrations, and the increases of nocturnal PBLH. With the aid of H2O2/HNO3, O3 formation in the YRD region is found to be easily affected by NOx in the future. The findings can help to understand the changing trend of O3 in the YRD region and can propose reasonable pollution control policies.

scholarly journals Regional severe particle pollution and its association with synoptic weather patterns in the Yangtze River Delta region, China

2017 ◽  
Vol 17 (21) ◽  
pp. 12871-12891 ◽  
Author(s):  
Lei Shu ◽  
Min Xie ◽  
Da Gao ◽  
Tijian Wang ◽  
Dexian Fang ◽  
...  
Keyword(s):  
Yangtze River Delta ◽  
Mean Value ◽  
Air Masses ◽  
Weather Patterns ◽  
Synoptic Weather ◽  
Particle Pollution ◽  
Pm2.5 And Pm10 ◽  
Marine Air ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Regional air pollution is significantly associated with dominant weather systems. In this study, the relationship between the particle pollution over the Yangtze River Delta (YRD) region and weather patterns is investigated. First, the pollution characteristics of particles in the YRD are studied using in situ monitoring data (PM2.5 and PM10) in 16 cities and Terra/MODIS AOD (aerosol optical depth) products collected from December 2013 to November 2014. The results show that the regional mean value of AOD is high in the YRD, with an annual mean value of 0.71±0.57. The annual mean particle concentrations in the cities of Jiangsu Province all exceed the national air quality standard. The pollution level is higher in inland areas, and the highest concentrations of PM2.5 and PM10 are 79 and 130 µg m−3, respectively, in Nanjing. The PM2.5  :  PM10 ratios are typically high, thus indicating that PM2.5 is the overwhelmingly dominant particle pollutant in the YRD. The wintertime peak of particle concentrations is tightly linked to the increased emissions during the heating season as well as adverse meteorological conditions. Second, based on NCEP (National Center for Environmental Prediction) reanalysis data, synoptic weather classification is conducted and five typical synoptic patterns are objectively identified. Finally, the synthetic analysis of meteorological fields and backward trajectories are applied to further clarify how these patterns impact particle concentrations. It is demonstrated that air pollution is more or less influenced by high-pressure systems. The relative position of the YRD to the anti-cyclonic circulation exerts significant effects on the air quality of the YRD. The YRD is largely influenced by polluted air masses from the northern and the southern inland areas when it is located at the rear of the East Asian major trough. The significant downward motion of air masses results in stable weather conditions, thereby hindering the diffusion of air pollutants. Thus, this pattern is quite favorable for the accumulation of pollutants in the YRD, resulting in higher regional mean PM10 (116.5 ± 66.9 µg m−3), PM2.5 (75.9 ± 49.9 µg m−3), and AOD (0.74) values. Moreover, this pattern is also responsible for the occurrence of most large-scale regional PM2.5 (70.4 %) and PM10 (78.3 %) pollution episodes. High wind speed and clean marine air masses may also play important roles in the mitigation of pollution in the YRD. Especially when the clean marine air masses account for a large proportion of all trajectories (i.e., when the YRD is affected by the cyclonic system or oceanic circulation), the air in the YRD has a lesser chance of being polluted. The observed correlation between weather patterns and particle pollution can provide valuable insight into making decisions about pollution control and mitigation strategies.

scholarly journals INVESTIGATING ALOFT AEROSOLS OVER CENTRAL-EASTERN CHINA USING CALIPSO MEASUREMENTS

2018 ◽  
Vol XLII-3/W5 ◽  
pp. 83-88
Author(s):  
J. Zou ◽  
K. Qin ◽  
J. Xu ◽  
X. Han
Keyword(s):  
North China ◽  
Rapid Development ◽  
Eastern China ◽  
Yangtze River Delta ◽  
Anthropogenic Source ◽  
Anthropogenic Aerosols ◽  
The North ◽  
Haze Pollution ◽  
Central Eastern ◽  
The Yrd

<p><strong>Abstract.</strong> The rapid development of China in the last decade has brought about serious environmental problems, among which the air quality has attracted much attention. Especially in the winter, haze events with PM<sub>2.5</sub> as the primary pollutant frequently occur, which has a huge strike on people's health. Such cumulative anthropogenic aerosols at surface over haze pollution regions could be lifted upwards by vertical turbulent mixing forming elevated haze layers that subsequent transport to distant regions. This paper attempts to analyze layer top altitude, ratio of anthropogenic source and optical properties by counting events occurring in aloft aerosols layer. CALIPSO satellite instruments are used for statistical analysis by screening layer data over central-eastern China from 2007 to 2016. In the most economically active and polluted areas of China, the North China Plain (NCP) and the Yangtze River Delta (YRD) are compared to analyze trend variations over ten years. Results shows that the frequency of occurrence of aloft layer in South China are higher than in North China, indicating that heat has a strong lifting effect on the planetary boundary layer (PBL). Further, the NCP has a unique high frequency value at 2.5<span class="thinspace"></span>km, while the YRD has two peaks, 3.5<span class="thinspace"></span>km and 2 km respectively. Moreover, in the past five years in the NCP (2011&amp;ndash;2016) and YRD (2012&amp;ndash;2016) regions, the anthropogenic source of pollutants dominated by smoke showed a downward trend year by year. In addition, monthly proportion of smoke and polluted dust are analyzed in NCP and YRD winter. Finally, the volume depolarization ratio is almost distributed within 0.2, indicating that the shape of the particles is irregular. The particulate color ratio has a sharp peak near 0.4&amp;ndash;0.7 suggesting that smaller particles dominate the size distribution during the winter months.</p>

scholarly journals Regional severe particle pollution and its association with synoptic weather patterns in the Yangtze River Delta region, China

2017 ◽  
Author(s):  
Lei Shu ◽  
Min Xie ◽  
Da Gao ◽  
Tijian Wang ◽  
Dexian Fang ◽  
...  
Keyword(s):  
Yangtze River ◽  
East Asian ◽  
Yangtze River Delta ◽  
Air Masses ◽  
East Asian Trough ◽  
Weather Patterns ◽  
Synoptic Weather ◽  
Particle Pollution ◽  
Pm2.5 And Pm10 ◽  
The Yangtze River Delta

Abstract. Regional air pollution is significantly associated with the dominant weather systems. In this study, the relationship between the particle pollution over the Yangtze River Delta (YRD) region and the weather patterns is investigated. Firstly, the pollution characteristics of particles (PM2.5 and PM10) in YRD are studied by using the in situ monitoring data in 16 cities from December 2013 to November 2014. The results show that the annual average concentrations in the cities of Jiangsu Province all exceed the national air quality standard. The pollution level is higher in the inland areas. Highest values can be found in Nanjing, with the concentrations of PM2.5 and PM10 being 79 μg · m−3 and 130  μg · m−3, respectively. The PM2.5/PM10 ratios are usually high in YRD, indicating that PM2.5 is the overwhelmingly dominant particle pollutant. The wintertime peak of particle concentrations is tightly linked to the increased emissions in the heating season and the poor meteorological condition. Secondly, based on NCEP reanalysis data, synoptic weather classification is conducted to reveal that the weather patterns are easy to cause heavy pollution in YRD. Five typical synoptic patterns are objectively identified, including the East Asian trough rear pattern, the depression inverted trough pattern, the transversal trough pattern, the high-pressure controlled pattern, and the northeast cold vortex pattern. Finally, synthetic analysis of meteorological fields and backward trajectory calculation are used to further clarify how these patterns impact particle concentrations. It is clarified that YRD is largely influenced by polluted air masses from the northern and the southern inland areas when it is at the rear of the East Asian major trough. In this case, the strong northwest wind hinders the vertical outward transport of pollutants. Thus, the East Asian trough rear pattern is quite favorable for the accumulation of pollutants in YRD, and respectively contributes 70.4 % and 78.3 % to the occurrence of large-scale regional PM2.5 and PM10 pollution episodes. While under the weather systems for other patterns, the clean marine air masses may play great roles in the mitigation of particle pollution in YRD. The correlation between weather patterns and particle pollution can provide valuable views in the decision-making on pollution control and mitigation strategies.

scholarly journals Cold fronts – a potential air quality threat over the Yangtze River Delta, China

2018 ◽  
Author(s):  
Hanqing Kang ◽  
Bin Zhu ◽  
Jinhui Gao ◽  
Yao He ◽  
Honglei Wang ◽  
...  
Keyword(s):  
Air Quality ◽  
Yangtze River ◽  
North China ◽  
Cold Front ◽  
Yangtze River Delta ◽  
Atmospheric Pollutants ◽  
Frontal Passage ◽  
Cold Fronts ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Cold frontal passages usually promote quick removal of atmospheric pollutants over North China (e.g. the Beijing–Tianjin–Hebei region). However, in the Yangtze River Delta (YRD), cold fronts pose a potential threat to air quality. In this study, a cold frontal passage and a subsequent stable weather event over YRD during 21–26 January 2015 was investigated with in-situ observations and Weather Research and Forecasting–Community Multiscale Air Quality Modeling System simulations. Observations showed a burst of PM2.5 pollution and an obvious southward motion of PM2.5 peaks on the afternoon of 21 January, suggesting a strong inflow of highly polluted airmasses to YRD by a cold frontal passage. Model simulations revealed an existing warm and polluted airmass over YRD, which climbed to the free troposphere along the frontal surface as the cold front passed, increasing the PM2.5 concentration at high altitudes. Strong north-westerly flow behind the cold front transported particles from the highly polluted North China Plain (NCP) to YRD. As the cold front intruded into the downstream of YRD, high pressure took control over the YRD, which resulted in a synoptic subsidence that brought particles from the free troposphere (1.0–2.0 km) to the surface. After the cold front's passage, weakened winds and a stable atmosphere stayed over the YRD and led to the accumulation of locally emitted PM2.5. Tagging of PM2.5 by geophysical regions showed that the PM2.5 contribution from the YRD itself was 35 % and the contribution from the NCP was 29 % during the cold frontal passage. However, under the subsequent stable weather conditions, the PM2.5 contribution from the YRD increased to 61.5 % and the contribution from the NCP decreased to 14.5 %. The results of this study indicate that cold fronts are potential bringers of atmospheric pollutants when there are strong air pollutant sources in upstream areas, which may deteriorate air quality in downstream regions.

scholarly journals Potential impacts of cold frontal passage on air quality over the Yangtze River Delta, China

2019 ◽  
Vol 19 (6) ◽  
pp. 3673-3685 ◽  
Author(s):  
Hanqing Kang ◽  
Bin Zhu ◽  
Jinhui Gao ◽  
Yao He ◽  
Honglei Wang ◽  
...  
Keyword(s):  
Air Quality ◽  
Yangtze River ◽  
North China ◽  
Frontal Zone ◽  
Yangtze River Delta ◽  
Atmospheric Pollutants ◽  
Frontal Passage ◽  
Cold Fronts ◽  
The Yrd ◽  
The Yangtze River Delta

Abstract. Cold frontal passages usually promote quick removal of atmospheric pollutants over North China (e.g. the Beijing–Tianjin–Hebei region). However, in the Yangtze River Delta (YRD), cold fronts may bring air pollutants from the polluted North China Plain (NCP), thereby deteriorating the air quality in the YRD. In this study, a cold frontal passage and a subsequent stable weather event over YRD during 21–26 January 2015 was investigated with in situ observations and Weather Research and Forecasting – Community Multiscale Air Quality Modeling System simulations. Observations showed a burst of PM2.5 pollution and an obvious southward motion of PM2.5 peaks on the afternoon of 21 January, suggesting a strong inflow of highly polluted air masses to YRD by a cold frontal passage. Model simulations revealed an existing warm and polluted air mass over YRD ahead of the frontal zone, which climbed to the free troposphere along the frontal surface as the cold front passed, increasing the PM2.5 concentration at high altitudes. Strong north-westerly frontal airflow transported particles from the highly polluted NCP to the YRD. As the frontal zone moved downstream of YRD, high pressure took control over the YRD, which resulted in a synoptic subsidence that trapped PM2.5 in the boundary layer. After the cold frontal episode, a uniform pressure field took control over the YRD. Locally emitted PM2.5 started to accumulate under the weak winds and stable atmosphere. Tagging of PM2.5 by geophysical regions showed that the PM2.5 contribution from the YRD itself was 35 % and the contribution from the NCP was 29 % during the cold frontal passage. However, under the subsequent stable weather conditions, the PM2.5 contribution from the YRD increased to 61.5 % and the contribution from the NCP decreased to 14.5 %. The results of this study indicate that cold fronts are potential carriers of atmospheric pollutants when there are strong air pollutant sources in upstream areas, which may deteriorate air quality in downstream regions.

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