scholarly journals Summertime fine particulate nitrate pollution in the North China Plain: Increasing trends, formation mechanisms, and implications for control policy

2018 ◽  
Author(s):  
Liang Wen ◽  
Likun Xue ◽  
Xinfeng Wang ◽  
Caihong Xu ◽  
Tianshu Chen ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Fine Particles ◽  
Nitrate Pollution ◽  
Effective Control ◽  
Formation Mechanisms ◽  
The North ◽  
The North China Plain ◽  
Holistic Understanding ◽  
Nitrate Aerosol

Abstract. Nitrate aerosol composes a significant fraction of fine particles and plays a key role in regional air quality and climate. To obtain a holistic understanding of the nitrate pollution and its formation mechanisms over the North China Plain (NCP) – the most industrialized and polluted region in northern China, intensive field observations were conducted at three sites during summertime in 2014–2015. The measurement sites include the downtown and downwind of Ji'nan, the capital city of Shandong Province, as well as the peak of NCP – Mt. Tai (1534 m a.s.l.), and hence cover representative urban, rural and remote areas of the region. Elevated nitrate concentrations were observed at all three sites despite distinct temporal and spatial variations. The nitrate / PM2.5 and nitrate / sulfate ratios have significantly increased in Ji'nan (2005–2015) and at Mt. Tai (from 2007 to 2014), indicating the worsening situation of regional nitrate pollution. A multi-phase chemical box model (RACM/CAPRAM) was deployed and constrained by observations to elucidate the nitrate formation mechanisms. The principal formation route is the partitioning of gaseous HNO3 to aerosol phase at daytime, whilst the nocturnal nitrate formation is dominated by the heterogeneous hydrolysis of N2O5. The daytime nitrate production in the NCP region is mainly limited by the availability of NO2 and to a lesser extent O3 and NH3, and the nighttime formation is controlled by both NO2 and O3. NH3 prompts significantly the nitrate formation at daytime but plays a slightly negative role in the nighttime. Our analyses suggest that controlling NOx and O3 is an efficient way at the moment to mitigate nitrate pollution in the NCP region, where NH3 is usually in excess in summer. This study provides observational evidence of rising trend of nitrate aerosol as well as scientific support for formulating effective control strategies for regional haze in China.

scholarly journals Summertime fine particulate nitrate pollution in the North China Plain: increasing trends, formation mechanisms and implications for control policy

2018 ◽  
Vol 18 (15) ◽  
pp. 11261-11275 ◽  
Author(s):  
Liang Wen ◽  
Likun Xue ◽  
Xinfeng Wang ◽  
Caihong Xu ◽  
Tianshu Chen ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Nitrate Pollution ◽  
Rural Site ◽  
Effective Control ◽  
Urban Site ◽  
Formation Mechanisms ◽  
The North ◽  
The North China Plain ◽  
Nitrate Aerosol

Abstract. Nitrate aerosol makes up a significant fraction of fine particles and plays a key role in regional air quality and climate. The North China Plain (NCP) is one of the most industrialized and polluted regions in China. To obtain a holistic understanding of the nitrate pollution and its formation mechanisms over the NCP region, intensive field observations were conducted at three sites during summertime in 2014–2015. The measurement sites include an urban site in downtown Jinan – the capital city of Shandong Province –, a rural site downwind of Jinan city, and a remote mountain site at Mt. Tai (1534 m a.s.l.). Elevated nitrate concentrations were observed at all three sites despite distinct temporal and spatial variations. Using historical observations, the nitrate ∕ PM2.5 and nitrate ∕ sulfate ratios have statistically significantly increased in Jinan (2005–2015) and at Mt. Tai (from 2007 to 2014), indicating the worsening situation of regional nitrate pollution. A multiphase chemical box model (RACM–CAPRAM) was deployed and constrained by observations to elucidate the nitrate formation mechanisms. The principal formation route is the partitioning of gaseous HNO3 to the aerosol phase during the day, whilst the nocturnal nitrate formation is dominated by the heterogeneous hydrolysis of N2O5. The daytime nitrate production in the NCP region is mainly limited by the availability of NO2 and to a lesser extent by O3 and NH3. In comparison, the nighttime formation is controlled by both NO2 and O3. The presence of NH3 contributes to the formation of nitrate aerosol during the day, while there is slightly decreasing nitrate formation at night. Our analyses suggest that controlling NOx and O3 is an efficient way, at the moment, to mitigate nitrate pollution in the NCP region, where NH3 is usually in excess in summer. This study provides observational evidence of a rising trend of nitrate aerosol as well as scientific support for formulating effective control strategies for regional haze in China.

On the difference of aerosol hygroscopicity between high and low RH environment in the North China Plain

2021 ◽  
Author(s):  
Jingnan Shi ◽  
Juan Hong ◽  
Nan Ma ◽  
Qingwei Luo ◽  
Hanbing Xu ◽  
...  
Keyword(s):  
Chemical Composition ◽  
North China Plain ◽  
North China ◽  
Experimental Period ◽  
Formation Mechanisms ◽  
Large Contribution ◽  
The North ◽  
The North China Plain ◽  
The Difference ◽  
Aerosol Hygroscopicity

<p>Simultaneous measurements of aerosol hygroscopicity and chemical composition were performed at a suburban site in the North China Plain in winter 2018 using a self-assembled hygroscopic tandem differential mobility analyzer (H-TDMA) and a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM), respectively. During the experimental period, aerosol particles usually show an external mixture in terms of hygroscopicity, with a less hygroscopic particles mode (LH) and a more hygroscopic mode (MH). The average ensemble mean hygroscopicity parameter (κ<sub>mean</sub>) are 0.16, 0.18, 0.16, and 0.15 for 60, 100, 150, and 200 nm particles, respectively. Two episodes with different RH/T conditions and secondary aerosol formations are distinguished. Higher aerosol hygroscopicity is observed for all measured sizes in the high RH episode (HRH) than in the low RH episode (LRH). In LRH, κ decreases as the particle size increases, which may be explained by the large contribution of non- or less-hygroscopic primary compounds in large particles due to the enhanced domestic heating emissions at low temperature. The number fraction of LH mode at 200 nm even exceeds 50%. Closure analysis is carried out between the HTDMA-measured κ and the ACSM-derived hygroscopicity using different approximations for the hygroscopic parameters of organic compounds (κ<sub>org</sub>). The results indicate that κ<sub>org</sub> is less sensitive towards the variation of its oxidation level under HRH conditions but has a stronger O: C-dependency under LRH conditions. The difference in the chemical composition and their corresponding physical properties under different RH/T conditions reflects potentially different formation mechanisms of secondary organic aerosols at those two distinct episodes.</p>

scholarly journals Contribution of hydroxymethanesulfonate (HMS) to severe winter haze in the North China Plain

2020 ◽  
Author(s):  
Tao Ma ◽  
Hiroshi Furutani ◽  
Fengkui Duan ◽  
Takashi Kimoto ◽  
Jingkun Jiang ◽  
...  
Keyword(s):  
Ion Chromatography ◽  
North China Plain ◽  
North China ◽  
Molar Ratio ◽  
Formation Mechanisms ◽  
Aerosol Formation ◽  
Severe Winter ◽  
The North ◽  
The North China Plain ◽  
High Concentrations

Abstract. Severe winter hazes accompanied by high concentrations of fine particulate matter (PM2.5) occur frequently in the North China Plain and threaten public health. Organic matter (OM) and sulfate are recognized as major components of PM2.5, while atmospheric models often fail to predict their high concentrations during severe winter hazes due to incomplete understanding of secondary aerosol formation mechanisms. By using a novel combination of single particle mass spectrometer and optimized ion chromatography measurement, here we show that hydroxymethanesulfonate (HMS), formed by the reaction between formaldehyde (HCHO) and dissolved SO2 in aerosol water, is ubiquitous in Beijing winter. The HMS concentration and the molar ratio of HMS to sulfate increased with the deterioration of winter haze. High concentrations of precursors (SO2 and HCHO) coupled with low oxidant levels, low temperature, high relative humidity, and moderately acid pH facilitate the heterogeneous formation of HMS, which could account for up to 15 % of OM in winter haze and lead to 36 % overestimates of sulfate when using traditional ion chromatography measurements. Despite the clean air actions have substantially reduced SO2 emissions, HMS concentration and molar ratio of HMS to sulfate during severe winter hazes increased from 2015 to 2016 with the growth of HCHO concentration. Our findings illustrate the significant contribution of heterogeneous HMS chemistry to severe winter hazes in Beijing, which help to improve the prediction of OM and sulfate, and suggest that the reduction in HCHO can help to mitigate haze pollution.

scholarly journals The distribution and trends of fog and haze in the North China Plain over the past 30 years

2014 ◽  
Vol 14 (11) ◽  
pp. 16123-16149 ◽  
Author(s):  
G. Q. Fu ◽  
W. Y. Xu ◽  
R. F. Rong ◽  
J. B. Li ◽  
C. S. Zhao
Keyword(s):  
Wind Speed ◽  
North China Plain ◽  
North China ◽  
Formation Mechanisms ◽  
The Past ◽  
The North ◽  
The North China Plain ◽  
Low Visibility ◽  
Increasing Trends ◽  
Fog Days

Abstract. Frequent low visibility, haze and fog events were found in the North China Plain (NCP). Data throughout the NCP during the past 30 years were examined to determine the horizontal distribution and decadal trends of low visibility, haze and fog events. The impact of meteorological factors such as wind and RH on those events was investigated. Results reveal distinct distributions of haze and fog days, due to their different formation mechanisms. Low visibility, haze and fog days all display increasing trends of before 1995, a steady stage during 1995–2003 and a drastically drop thereafter. All three events occurred most frequently during the heating season. Benefiting from emission control measures, haze and fog both show decreasing trends in winter during the past 3 decades, while summertime haze displays continuous increasing trends. The distribution of wind speed and wind direction as well as the topography within the NCP has determinative impacts on the distribution of haze and fog. Weakened south-easterly winds in the southern part of the NCP has resulted in high pollutant concentrations and frequent haze events along the foot of the Taihang Mountains. The orographic wind convergence zone in the central band area of the southern NCP is responsible for the frequent fog events in this region. Wind speed has been decreasing throughout the entire southern NCP, resulting in more stable atmospheric conditions and weaker dispersion abilities, calling for harder efforts to control emissions to prevent haze events. Haze events are strongly influenced by the ambient RH. RH values associated with haze days are evidently increasing, suggesting that an increasing fraction of haze events are caused by the hygroscopic growth of aerosols, rather than simply by high aerosol loadings.

scholarly journals Role of ambient ammonia in particulate ammonium formation at a rural site in the North China Plain

2017 ◽  
Author(s):  
Zhaoyang Meng ◽  
Xiaobin Xu ◽  
Weili Lin ◽  
Yulin Xie ◽  
Bo Song ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Meteorological Conditions ◽  
Water Soluble ◽  
Precipitation Event ◽  
Rural Site ◽  
Formation Mechanisms ◽  
The North ◽  
The North China Plain ◽  
Particulate Ammonium

Abstract. The real-time measurements of NH3 and trace gases were conducted, in conjunction with semi-continuous measurements of water-soluble ions in PM2.5 at a rural site in the North China Plain (NCP) from May to September 2013 in order to better understand of chemical characteristics for ammonia, and of the impact on formation of secondary ammonium aerosols in the NCP. Extremely high NH3 and NH4+ concentrations were observed after a precipitation event within 7–10 days following urea application. Elevated NH3 levels coincided with elevated NH4+, suggesting that NH3 plays a vital role in enhancing particulate ammonium. For the sampling period, the average oxidation/conversion ratios for SO42− (SOR), NO3− (NOR) and NH4+ (NHR) were estimated to be 64 %, 24 % and 30 %, respectively. The increased NH3 concentrations mainly from agricultural activities, coincided with the prevailing meteorological conditions could promote the secondary transformation, resulting in higher hourly SOR, NOR and NHR. The concentrations of NH3, NH4+, and NHR had clear diurnal variations, which could be attributed to their sources, meteorological conditions, and formation mechanisms. The back trajectory analysis indicates that the transport of air masses from the North China Plain region contributed to the atmospheric NH3 variations, and both regional sources and long-distance transport from southeast played important roles in the observed ammonium aerosol at rural site in the NCP. The findings of this study are expected to facilitate developing future NH3 emission control policies for the North China Plain.

scholarly journals Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN): integrated analysis and intensive winter campaign 2018

2021 ◽  
Author(s):  
Guo Li ◽  
Hang Su ◽  
Nan Ma ◽  
Jiangchuan Tao ◽  
Ye Kuang ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Physicochemical Properties ◽  
North China Plain ◽  
North China ◽  
Fine Particles ◽  
Integrated Analysis ◽  
The North ◽  
Multiphase Reactions ◽  
The North China Plain ◽  
Chemistry Experiment

High-RH-favored multiphase reactions can significantly change the chemical composition of fine particles and thereby modify their physicochemical properties.

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