Fog Droplet Size Distribution and the Interaction between Fog Droplets and Fine Particles during Dense Fog in Tianjin, China

Abstract

From November 2016 to January 2017, there were large-scale dense fog processes in Tianjin area on the west coast of Bohai Bay, China, even strong dense fog with visibility less than 50 m occurred. Based on the observation data of fog droplet spectrum monitor, visibility sensor, environmental particle monitoring equipment and meteorological automatic station, the characteristics of fog droplet size distribution and the interaction between the fog droplets and fine particles during dense fog events were analyzed. The results show following characteristics: (1) The average concentration of fog droplets (Na), the average liquid water content (La) and the maximum liquid water content (Lmax) in the strong dense fog process are larger than those in the dense fog. The average spectrum of fog droplet size distribution conforms to Junge distribution, and they are all broad-spectrum fog with a spectrum width of about 45 μm. The average spectrum is similar to the dense fog of heavily industrialized inland in the world. (2) The maximum of fog droplet diameter during the formation stage have a good indication for the outbreak of strong dense fog. (3) The mass concentration of PM2.5 (CPM2.5) is ranged from 121–375 μg/m3, and the interaction between fog droplets and fine particles is analyzed. During the formation, development and maturity stages, fog process can scavenge atmospheric fine particles, and the scavenging efficiency of PM2.5 is more remarkable than PM10. When CPM2.5 does not exceed 350 μg/m3, the increase in the concentration of fine particles is conducive to the rapid growth of fog droplets and the sharp drop of visibility. However, when CPM2.5 exceeds the critical value, the increase has a negative feedback effect on the development of the fog process. More investigations and cases are necessary to fully assess the mechanisms related to the dense fog events in Tianjin area and further analysis will be done.

The Microphysical Properties of a Sea-Fog Event along the West Coast of the Yellow Sea in Spring

“…The mean value of the LWC was 0.057 g m −3 , the mean value of the radius was 4.0 µm, and the mean value of the NUM was 64.4 cm −3 during these two fog events. The mean value of LWC is comparable with that observed (0.041 g m −3 ) in Tianjin [20], but the mean value of NUM is only 10.8% with that observed (596 cm −3 ) in Tianjin. With a lot of condensation nuclei in an industrial city (Tianjin), water vapor condenses on condensation nuclei, producing a large number of small droplets [1].…”

“…Using visibility as the criterion, the fogging process can be divided into three stages: the formation stage (when the visibility drops from 1000 m to its lowest level), the development stage (after the visibility drops to its lowest level and remains basically constant for more than 30 min), and the dissipation stage (when the visibility increases noticeably from the lowest value to 1000 m) [20]. Figure 5 shows the size distribution characteristics of fog droplets at each stage during the two fog periods.…”

“…where r and n(r) are droplet radii and the number of droplets, respectively, and N 0 , λ, and μ are the intercept, slope, and shape parameters, respectively [14]. Based on Equation (7), Liu (1992Liu ( , 1993 [8,22] proposed a simple statistical method to identify the statistical distribution pattern, which was used to investigate if the statistical pattern of the fog DSD follows the Gamma distribution, skewness (S k ) and kurtosis (K u ) are defined as: Using visibility as the criterion, the fogging process can be divided into three stages: the formation stage (when the visibility drops from 1000 m to its lowest level), the development stage (after the visibility drops to its lowest level and remains basically constant for more than 30 min), and the dissipation stage (when the visibility increases noticeably from the lowest value to 1000 m) [20]. Figure 5 shows the size distribution characteristics of fog droplets at each stage during the two fog periods.…”

Observation, Simulation and Predictability of Fog: Review and Perspectives

“…Fog formation involves a myriad of interactions between physical processes, generating fog variability in time and space. Once a fog layer has been formed, the number of fog droplets and their size distribution can have a large impact on the development of the fog layer due to their feedback on gravitational settling and radiative cooling at the fog top, which are key processes for fog [6][7][8][9]. In the past 30 years, more and more attention has been paid to the study of the microphysical characteristics of fog, and continuous progress had been made in the development of observation instruments of fog microphysical parameters [6].…”

Experimental study on the evolution of droplets size distribution during the fog life cycle

“…Both N d and D ef f have a particularly large impact on the development of the fog layer due to their feedback on gravitational settling, LWC and radiative cooling at the fog top (Stolaki et al, 2015;Maalick et al, 2016;Boutle et al, 2018;Schwenkel and Maronga, 2018;Kutty et al, 2021). In situ measurements of fog microphysics have shown a large variability of these parameters: LWC, N d and D ef f are commonly in the range 0.01-0.5 g.m −3 , 10-500 cm −3 and 10-20 µm in diameter, respectively (Pilié et al, 1975;Choularton et al, 1981;Gerber, 1991;Wendisch et al, 1998;Liu et al, 2011;Lu et al, 2013;Niu et al, 2010;Price, 2011;Zhao et al, 2013;Gultepe et al, 2019;Liu et al, 2020). Large spatial and temporal variabilities have also been noticed during individual fog events, and even at different heights of fog layers (Okita, 1962;Pilié et al, 1975;Goodman, 1977;Pinnick et al, 1978;Garcıa-Garcıa et al, 2002).…”