Organic aerosol volatility and viscosity in the North China Plain: contrast between summer and winter

Abstract. Volatility and viscosity have substantial impacts on gas–particle partitioning, formation and evolution of aerosol and hence the predictions of aerosol-related air quality and climate effects. Here aerosol volatility and viscosity at a rural site (Gucheng) and an urban site (Beijing) in the North China Plain (NCP) in summer and winter were investigated by using a thermodenuder coupled with a high-resolution aerosol mass spectrometer. The effective saturation concentration (C*) of organic aerosol (OA) in summer was smaller than that in winter (0.55 µg m−3 vs. 0.71–0.75 µg m−3), indicating that OA in winter in the NCP is more volatile due to enhanced primary emissions from coal combustion and biomass burning. The volatility distributions varied and were largely different among different OA factors. In particular, we found that hydrocarbon-like OA (HOA) contained more nonvolatile compounds compared to coal-combustion-related OA. The more oxidized oxygenated OA (MO-OOA) showed overall lower volatility than less oxidized OOA (LO-OOA) in both summer and winter, yet the volatility of MO-OOA was found to be relative humidity (RH) dependent showing more volatile properties at higher RH. Our results demonstrated the different composition and chemical formation pathways of MO-OOA under different RH levels. The glass transition temperature (Tg) and viscosity of OA in summer and winter are estimated using the recently developed parameterization formula. Our results showed that the Tg of OA in summer in Beijing (291.5 K) was higher than that in winter (289.7–290.0 K), while it varied greatly among different OA factors. The viscosity suggested that OA existed mainly as solid in winter in Beijing (RH = 29 ± 17 %), but as semisolids in Beijing in summer (RH = 48 ± 25 %) and Gucheng in winter (RH = 68 ± 24 %). These results have the important implication that kinetically limited gas–particle partitioning may need to be considered when simulating secondary OA formation in the NCP.

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Organic aerosol volatility and viscosity in North China Plain: Contrast between summer and winter

10.5194/acp-2020-1105 ◽

2020 ◽

Author(s):

Weiqi Xu ◽

Chun Chen ◽

Yanmei Qiu ◽

Ying Li ◽

Zhiqiang Zhang ◽

...

Keyword(s):

Coal Combustion ◽

North China Plain ◽

North China ◽

Organic Aerosol ◽

Rural Site ◽

Urban Site ◽

Aerosol Mass ◽

Effective Saturation ◽

Formation And Evolution ◽

Primary Emissions

Abstract. Volatility and viscosity have substantial impacts on gas-particle partitioning, formation and evolution of aerosol, and hence the predictions of aerosol related air quality and climate effects. Here aerosol volatility and viscosity at a rural site (Gucheng) and an urban site (Beijing) in North China Plain (NCP) in summer and winter were investigated by using a thermodenuder coupled with high resolution aerosol mass spectrometer. The effective saturation concentration (C*) of organic aerosol (OA) in summer was smaller than that in winter (0.55 μg m−3 vs. 0.71–0.75 μg m−3), indicating that OA in winter in NCP is more volatile due to enhanced primary emissions from coal combustion and biomass burning. The volatility distributions varied largely different among different OA factors. In particular, we found that hydrocarbon-like OA (HOA) contained more non-volatile compounds compared to coal combustion related OA. The more oxidized oxygenated OA (MO-OOA) showed overall lower volatility than less oxidized OOA (LO-OOA) in both summer and winter, yet the volatility of MO-OOA was found to be relative humidity (RH) dependent showing more volatile properties at higher RH. Our results demonstrated the different composition and chemical formation pathways of MO-OOA under different RH levels. The glass transition temperature (Tg) and viscosity of OA in summer and winter are estimated using the recently developed parameterization formula. Our results showed that the Tg of OA in summer in Beijing (291.5 K) was higher than that in winter (289.7–290.0 K), while it varied greatly among different OA factors. The viscosity suggested that OA existed mainly as solid in winter in Beijing, but as semi-solids in Beijing in summer and Gucheng in winter. These results have important implications that kinetically limited gas-particle partitioning may need to be considered when simulating secondary OA formation in NCP.

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Aerosol vertical mass flux measurements during heavy aerosol pollution episodes at a rural site and an urban site in the Beijing area of the North China Plain

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-12857-2019 ◽

2019 ◽

Vol 19 (20) ◽

pp. 12857-12874 ◽

Cited By ~ 1

Author(s):

Renmin Yuan ◽

Xiaoye Zhang ◽

Hao Liu ◽

Yu Gui ◽

Bohao Shao ◽

...

Keyword(s):

Mass Flux ◽

North China Plain ◽

North China ◽

Rural Site ◽

Urban Site ◽

The North ◽

The North China Plain ◽

Aerosol Pollution ◽

The Mean ◽

Pollution Episodes

Abstract. Due to excessive anthropogenic emissions, heavy aerosol pollution episodes (HPEs) often occur during winter in the Beijing–Tianjin–Hebei (BTH) area of the North China Plain. Extensive observational studies have been carried out to understand the causes of HPEs; however, few measurements of vertical aerosol fluxes exist, despite them being the key to understanding vertical aerosol mixing, specifically during weak turbulence stages in HPEs. In the winter of 2016 and the spring of 2017 aerosol vertical mass fluxes were measured by combining large aperture scintillometer (LAS) observations, surface PM2.5 and PM10 mass concentrations, and meteorological observations, including temperature, relative humidity (RH), and visibility, at a rural site in Gucheng (GC), Hebei Province, and an urban site at the Chinese Academy of Meteorological Sciences (CAMS) in Beijing located 100 km to the northeast. These are based on the light propagation theory and surface-layer similarity theory. The near-ground aerosol mass flux was generally lower in winter than in spring and weaker in rural GC than in urban Beijing. This finding provides direct observational evidence for a weakened turbulence intensity and low vertical aerosol fluxes in winter and polluted areas such as GC. The HPEs included a transport stage (TS), an accumulative stage (AS), and a removal stage (RS). During the HPEs from 25 to 31 January 2017, in Beijing, the mean mass flux decreased by 51 % from 0.0049 mg m−2 s−1 in RSs to 0.0024 mg m−2 s−1 in the TSs. During the ASs, the mean mass flux decreased further to 0.00087 mg m−2 s−1, accounting for approximately one-third of the flux in the TSs. A similar reduction from the TSs to ASs was observed in the HPE from 16 to 22 December 2016 in GC. It can be seen that from the TS to the AS, the aerosol vertical turbulent flux decreased, but the aerosol particle concentration within the surface layer increased, and it is inferred that in addition to the contribution of regional transport from upwind areas during the TS, suppression of vertical turbulence mixing confining aerosols to a shallow boundary layer increased accumulation.

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Aerosol Vertical Mass Flux Measurements During Heavy Aerosol Pollution Episodes at a Rural Site and an Urban Site in the Beijing Area of the North China Plain

10.5194/acp-2018-1265 ◽

2019 ◽

Author(s):

Renmin Yuan ◽

Xiaoye Zhang ◽

Hao Liu ◽

Yu Gui ◽

Bohao Shao ◽

...

Keyword(s):

Mass Flux ◽

North China Plain ◽

North China ◽

Rural Site ◽

Urban Site ◽

The North ◽

The North China Plain ◽

Aerosol Pollution ◽

The Mean ◽

Pollution Episodes

Abstract. Due to excessive anthropogenic emissions, heavy aerosol pollution episodes (HPEs) often occur during winter in the Beijing-Tianjin-Hebei (BTH) area of the North China Plain. Extensive observational studies have been carried out to understand the causes of HPEs; however, few measurements of aerosol vertical fluxes exist, despite them being the key to understanding vertical aerosol mixing, specifically during weak turbulence stages in HPEs. In the winter of 2016 and the spring of 2017, based on the light propagation theory and surface-layer similarity theory, aerosol vertical mass fluxes were measured by combining large aperture scintillometer (LAS) observations, surface PM2.5 and PM10 mass concentrations, and meteorological observations, including temperature, relative humidity (RH), and visibility, at a rural site in Gucheng (GC), Hebei Province, and an urban site at the Chinese Academy of Meteorological Sciences (CAMS) in Beijing located 100 km to the northeast. The near-ground aerosol mass flux was generally lower in winter than in spring and weaker in rural GC than in urban Beijing. This finding provides direct observational evidence from the perspective of vertical aerosol fluxes for a weakened turbulence intensity in winter and in polluted areas such as GC. The HPEs included a transport stage (TS), an accumulative stage (AS), and a removal stage (RS). During the HPEs from January 25, 2017 to January 31, 2017, in Beijing, the mean mass flux decreased by 51 % from 0.0049 mg m−2 s−1 in RSs to 0.0024 mg m−2 s−1 in the TSs. During the ASs, the mean mass flux decreased further to 0.00087 mg m−2 s−1, accounting for approximately 1/3 of the flux in the TSs. A similar reduction from the TSs to ASs was observed in the HPE from December 16, 2016 to December 22, 2016 in GC. The weakened mass flux indicates that the already weak turbulence would be further weakened by aerosol pollution to a certain extent, which would further facilitate aerosol accumulation.

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Estimation of particulate organic nitrates from thermodenuder–aerosol mass spectrometer measurements in the North China Plain

Atmospheric Measurement Techniques ◽

10.5194/amt-14-3693-2021 ◽

2021 ◽

Vol 14 (5) ◽

pp. 3693-3705

Author(s):

Weiqi Xu ◽

Masayuki Takeuchi ◽

Chun Chen ◽

Yanmei Qiu ◽

Conghui Xie ◽

...

Keyword(s):

Mass Spectrometer ◽

North China Plain ◽

North China ◽

Rural Site ◽

Organic Nitrates ◽

Aerosol Mass Spectrometer ◽

The North ◽

Aerosol Mass ◽

Inorganic Nitrate ◽

The North China Plain

Abstract. Particulate organic nitrates (pON) are an important component of secondary organic aerosol in biogenic-emission-dominant environments and play a critical role in NOx cycles. However, estimation of pON has been a challenge in polluted environments, e.g., North China Plain, with high concentrations of inorganic nitrate and NOx. Here we developed a method for estimation of pON from the measurements of high-resolution aerosol mass spectrometer coupled with a thermodenuder based on the volatility differences between inorganic nitrate and pON. The results generally correlated well with those estimated from positive matrix factorization of combined organic and inorganic mass spectra and from the ratio of NO+ to NO2+ (NOx+ ratio), yet they had improvements in reducing negative values due to the influences of high concentration of inorganic nitrate and constant NOx+ ratio of organic nitrates (RON). By applying this approach to the measurements at an urban (Beijing) and a rural site (Gucheng) in summer and winter in the North China Plain, we estimated that the average mass concentrations of NO3,org (1.8 µg m−3 vs. 1.0 µg m−3) and pON to OA (27.5 % vs. 14.8 %) were higher in summer than in winter in Beijing, indicating more pON formation in biogenically and anthropogenically mixed environments. In addition, the average NO3,org loading in Gucheng was 1.9 µg m−3, and the pON at the rural site also showed higher contribution to OA than that in Beijing during wintertime due to higher primary emissions and gaseous precursors in Gucheng. In addition, RON was determined and showed considerable differences between day–night and clean–polluted periods, highlighting the complexity of pON compounds from different chemical pathways (e.g., OH and NO3 oxidation) and sources.

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Measurement report: On the difference of aerosol hygroscopicity between high and low RH conditions in the North China Plain

10.5194/acp-2021-1010 ◽

2022 ◽

Author(s):

Jingnan Shi ◽

Juan Hong ◽

Nan Ma ◽

Qingwei Luo ◽

Yao He ◽

...

Keyword(s):

Chemical Composition ◽

North China Plain ◽

North China ◽

Rural Site ◽

Formation Processes ◽

The North ◽

The North China Plain ◽

Secondary Formation ◽

Primary Emissions ◽

Aerosol Hygroscopicity

Abstract. Atmospheric processes, including both primary emissions and secondary formation, may exert complex effects on aerosol hygroscopicity, which is of significant importance in understanding and quantifying the effect of aerosols on climate and human health. In order to explore the influence of local emissions and secondary formation processes on aerosol hygroscopicity, we investigated the hygroscopic properties of submicron aerosol particles at a rural site in the North China Plain (NCP) in winter 2018. This was conducted by simultaneous measurements of aerosol hygroscopicity and chemical composition, using a self-assembled hygroscopic tandem differential mobility analyzer (HTDMA) and a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM). The hygroscopicity results showed that the particles during the entire campaign were mainly externally mixed, with a more hygroscopic (MH) mode and a less hygroscopic (LH) particles mode. The mean hygroscopicity parameter values (κmean) derived from hygroscopicity measurements for particles at 60, 100, 150, and 200 nm were 0.16, 0.18, 0.16, and 0.15, respectively. During this study, we classified two distinct episodes with different RH/T conditions, indicative of different primary emissions and secondary formation processes. It was observed that aerosols at all measured sizes were more hygroscopic under the high RH (HRH) episode than those under the low RH (LRH) episode. During the LRH, κ decreased with increasing particle size, which may be explained by the enhanced domestic heating at low temperature, causing large emissions of non- or less-hygroscopic primary aerosols. This is particularly obvious for 200 nm particles, with a dominant number fraction (> 50 %) of LH mode particles. Using O : C-dependent hygroscopic parameters of secondary organic compounds (κSOA), closure analysis between the HTDMA_measured κ and the ACSM_derived κ was carried out. The results showed that κSOA under the LRH episode was less sensitive to the changes in organic oxidation level, while κSOA under the HRH had a relatively stronger dependency on the organic O : C. This feature suggests that the different sources and aerosol evolution processes, partly resulting from the variation in atmospheric RH/T conditions, may lead to significant changes in aerosol chemical composition, which will further influence their corresponding physical properties.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-11261-2018 ◽

2018 ◽

Vol 18 (15) ◽

pp. 11261-11275 ◽

Cited By ~ 42

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.

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