A parameterization of low visibilities for hazy days in the North China Plain

Chen, J.; Zhao, Chunsheng; Ma, Nan; Liu, P. F.; Göbel, T.; Hallbauer, E.; Deng, Zhaoze; Ran, Liang; Xu, Wanyun; Liang, Ze; Liu, H. J.; Yan, Peng; Zhou, Xiuji; Wiedensohler, Alfred

doi:10.5194/acp-12-4935-2012

Cited by 138 publications

(117 citation statements)

References 68 publications

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“…Atmospheric humidity is a major factor affecting the particle properties, as aerosols can grow by the uptake of water. When relative humidity (RH) is larger than 95 %, the atmospheric visibility can be critically reduced (Chen et al, 2012). When RH is larger than 100 %, some of the hygroscopic aerosols can be activated and form fog droplets (Pruppacher and Klett, 1978).…”

Section: Introductionmentioning

confidence: 99%

Quantifying the relationship between PM2.5 concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

et al. 2018

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Abstract. Air quality and visibility are strongly influenced by aerosol loading, which is driven by meteorological conditions. The quantification of their relationships is critical to understanding the physical and chemical processes and forecasting of the polluted events. We investigated and quantified the relationship between PM 2.5 (particulate matter with aerodynamic diameter is 2.5 µm and less) mass concentration, visibility and planetary boundary layer (PBL) height in this study based on the data obtained from four long-lasting haze events and seven fog-haze mixed events from January 2014 to March 2015 in Beijing. The statistical results show that there was a negative exponential function between the visibility and the PM 2.5 mass concentration for both haze and fog-haze mixed events (with the same R 2 of 0.80). However, the fog-haze events caused a more obvious decrease of visibility than that for haze events due to the formation of fog droplets that could induce higher light extinction. The PM 2.5 concentration had an inversely linear correlation with PBL height for haze events and a negative exponential correlation for fog-haze mixed events, indicating that the PM 2.5 concentration is more sensitive to PBL height in fog-haze mixed events. The visibility had positively linear correlation with the PBL height with an R 2 of 0.35 in haze events and positive exponential correlation with an R 2 of 0.56 in foghaze mixed events. We also investigated the physical mechanism responsible for these relationships between visibility, PM 2.5 concentration and PBL height through typical haze and fog-haze mixed event and found that a double inversion layer formed in both typical events and played critical roles in maintaining and enhancing the long-lasting polluted events. The variations of the double inversion layers were closely associated with the processes of long-wave radiation cooling in the nighttime and short-wave solar radiation reduction in the daytime. The upper-level stable inversion layer was formed by the persistent warm and humid southwestern airflow, while the low-level inversion layer was initially produced by the surface long-wave radiation cooling in the nighttime and maintained by the reduction of surface solar radiation in the daytime. The obvious descending process of the upper-level inversion layer induced by the radiation process could be responsible for the enhancement of the lowlevel inversion layer and the lowering PBL height, as well as high aerosol loading for these polluted events. The reduction of surface solar radiation in the daytime could be around 35 % for the haze event and 94 % for the fog-haze mixed event. Therefore, the formation and subsequent descending processes of the upper-level inversion layer should be an important factor in maintaining and strengthening the longlasting severe polluted events, which has not been revealed in previous publications. The interactions and feedbacks between PM 2.5 concentration and PBL height linked by radiation process caused a more significant an...

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Section: Introductionmentioning

confidence: 99%

Quantifying the relationship between PM2.5 concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

et al. 2018

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“…Similarly, uncertainties in the scattering coefficient computed by Mie theory were evaluated at 20 %, and at 30 % for the absorption coefficient by Wex et al (2002), at 34 % for the extinction coefficient by Chen et al (2012), and at 50 % by .…”

Section: Computation Of the Particle Extinction Coefficientmentioning

confidence: 99%

“…Consequently, under conditions of relative humidity larger than 95 %, the aerosol radiative forcing can increase by 60 % (Adams et al, 1999), and atmospheric visibility can be critically reduced (e.g. Chen et al, 2012). At relative humidities larger than 100 %, water condenses on some aerosols which are activated, and form fog droplets (e.g.…”

Section: Introductionmentioning

confidence: 99%

Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Elías¹,

Dupont

Hammer

et al. 2015

Atmos. Chem. Phys.

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Abstract. The study assesses the contribution of aerosols to the extinction of visible radiation in the mist-fog-mist cycle. Relative humidity is large in the mist-fog-mist cycle, and aerosols most efficient in interacting with visible radiation are hydrated and compose the accumulation mode. Measurements of the microphysical and optical properties of these hydrated aerosols with diameters larger than 0.4 µm were carried out near Paris, during November 2011, under ambient conditions. Eleven mist-fog-mist cycles were observed, with a cumulated fog duration of 96 h, and a cumulated mist-fogmist cycle duration of 240 h.In mist, aerosols grew by taking up water at relative humidities larger than 93 %, causing a visibility decrease below 5 km. While visibility decreased down from 5 to a few kilometres, the mean size of the hydrated aerosols increased, and their number concentration (N ha ) increased from approximately 160 to approximately 600 cm −3 . When fog formed, droplets became the strongest contributors to visible radiation extinction, and liquid water content (LWC) increased beyond 7 mg m −3 . Hydrated aerosols of the accumulation mode co-existed with droplets, as interstitial non-activated aerosols. Their size continued to increase, and some aerosols achieved diameters larger than 2.5 µm. The mean transition diameter between the aerosol accumulation mode and the small droplet mode was 4.0 ± 1.1 µm. N ha also increased on average by 60 % after fog formation. Consequently, the mean contribution to extinction in fog was 20 ± 15 % from hydrated aerosols smaller than 2.5 µm and 6 ± 7 % from larger aerosols. The standard deviation was large because of the large variability of N ha in fog, which could be smaller than in mist or 3 times larger.The particle extinction coefficient in fog can be computed as the sum of a droplet component and an aerosol component, which can be approximated by 3.5 N ha (N ha in cm −3 and particle extinction coefficient in Mm −1 ). We observed an influence of the main formation process on N ha , but not on the contribution to fog extinction by aerosols. Indeed, in fogs formed by stratus lowering (STL), the mean N ha was 360 ± 140 cm −3 , close to the value observed in mist, while in fogs formed by nocturnal radiative cooling (RAD) under cloud-free sky, the mean N ha was 600 ± 350 cm −3 . But because visibility (extinction) in fog was also lower (larger) in RAD than in STL fogs, the contribution by aerosols to extinction depended little on the fog formation process. Similarly, the proportion of hydrated aerosols over all aerosols (dry and hydrated) did not depend on the fog formation process.Measurements showed that visibility in RAD fogs was smaller than in STL fogs due to three factors: (1) LWC was larger in RAD than in STL fogs, (2) droplets were smaller, (3) hydrated aerosols composing the accumulation mode were more numerous.

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“…In this way hygroscopic and optical properties can be understood to have a strong linkage. Supposing that non-light-absorbing material is uniformly mixed with water after hygroscopic growth, we can determine the changes in volume of both the real and imaginary parts of the particles, and then we can calculate the extinction coefficient of the particles (Chen et al, 2012). Therefore, we can calculate the extinction properties of the particles accurately at different levels of RH based on the Mie theory according to the three-component model, as long as we obtain the total volume concentration, the volume fraction of EC of the observed aerosols, the hygroscopic parameter (κ) of the observed aerosols, and the hypothesized mixed mode of the observed aerosols.…”

Section: Introductionmentioning

confidence: 99%

Analysis of extinction properties as a function of relative humidity using a κ-EC-Mie model in Nanjing

Zhang

Shen²,

et al. 2017

Atmos. Chem. Phys.

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Abstract. The relationship between relative humidity (RH) and extinction properties is of widespread concern. In this study, a hygroscopic parameter (κ) and the volume fraction of elemental carbon (EC) were used to characterize the chemical characteristics of particles, and a core-shell model was built based on these characteristics. The size distribution, chemical composition, and RH were measured in Nanjing from 15 October to 13 November 2013. The modelderived extinction coefficients of particles were fit with the program of coated spheres according to Bohren and Huffman (2008) (BHCOAT), and the modeled values correlated well with the measurement-derived extinction coefficients (r 2 = 0.81), which suggested that the core-shell model produced reasonable results. The results show that more than 81 % of the extinction coefficient in Nanjing was due to particles in the 0.2-1.0 µm size range. Under dry conditions, the higher mass fraction of particles in the 0.2-1.0 µm size range caused the higher extinction coefficient. An increase in RH led to a significant increase in the extinction coefficient, although the increases differed among the different size segments. For λ = 550 nm, the extinction coefficient from the 0.01-0.2, 0.2-0.5, and 1.0-2.0 µm size ranges increased significantly with the increase in RH, whereas the extinction contributions from the 0.5-1.0 and 2.0-10.0 µm size ranges to the extinction coefficient decreased slightly.

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A parameterization of low visibilities for hazy days in the North China Plain

Cited by 138 publications

References 68 publications

Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Analysis of extinction properties as a function of relative humidity using a <i>κ</i>-EC-Mie model in Nanjing

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A parameterization of low visibilities for hazy days in the North China Plain

Cited by 138 publications

References 68 publications

Quantifying the relationship between PM&lt;sub&gt;2.5&lt;/sub&gt; concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Quantifying the relationship between PM&lt;sub&gt;2.5&lt;/sub&gt; concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Analysis of extinction properties as a function of relative humidity using a &lt;i&gt;κ&lt;/i&gt;-EC-Mie model in Nanjing

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Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Analysis of extinction properties as a function of relative humidity using a <i>κ</i>-EC-Mie model in Nanjing