Fog Events Research Articles

Impact of the Changbai Mountains’ topography on spring fog over the Bohai Sea

Fog is a highly complex weather phenomenon influenced by numerous factors. This study investigated the impact of the Changbai Mountains’ topography on the formation and development of spring fog in the Bohai Sea. From 12 to 14 May 2021, the Bohai region experienced a sea fog event. Utilizing Himawari-8 satellite data, ERA5 reanalysis dataset, land and sea station observations, the WRF model, a topography sensitivity experiment, and backward trajectory tracking, the influence of the Changbai Mountains’ topography on the evolution of this sea fog event was assessed. Results indicated that the Changbai Mountains’ topography significantly impacted the propagation and concentration of the sea fog through dual effects—namely, the Venturi Effect and Foehn Clearance Effect. Comparative simulations incorporating and excluding the Changbai Mountains revealed that its topography favored weak convergence (Venturi Effect) of low-level airflow over the Bohai Sea induced by a high-pressure system, promoting westward fog expansion. Additionally, the backward trajectory analysis further indicated that the Foehn Clearance Effect of the Changbai Mountains extended its influence far beyond the immediate lee side, contributing to significant changes in atmospheric conditions such as reductions in relative humidity and increases in potential temperature. The dry, warm foehn contributed to a reduction in the liquid water content, ultimately leading to the weakening or even dissipation of the sea fog in the region close to the Changbai Mountains. This study emphasizes the crucial role of the Changbai Mountains’ topography in the development and evolution of fog, providing valuable insights for forecasting fog in regions with complex terrain.

Implementation of WRF‐Urban Asymmetric Convective Model (UACM) for Simulating Urban Fog Over Delhi, India

AbstractAccurate fog prediction in densely urbanized cities poses a challenge due to the complex influence of urban morphology on meteorological conditions in the urban roughness sublayer. This study implemented a coupled WRF‐Urban Asymmetric Convective Model (WRF‐UACM) for Delhi, India, integrating explicit urban physics with Sentinel‐updated USGS land‐use and urban morphological parameters derived from the UT‐GLOBUS dataset. When evaluated against the baseline Asymmetric Convective Model (WRF‐BACM) using Winter Fog Experiment (WiFEX) data, WRF‐UACM significantly improved urban meteorological variables such as diurnal variations in 10‐m wind speed, 2‐m air temperature (T2), and 2‐m relative humidity (RH2) during a fog event. UACM also demonstrates improved accuracy in simulating temperature and significantly reducing biases for wind speed and daytime RH2 under clear sky conditions. UACM reproduced the nighttime urban heat island effect within the city, showing realistic diurnal heating and cooling patterns that are important for accurate fog onset and duration. UACM effectively predicts the onset, evolution, and dissipation of fog, aligning well with observed data and satellite imagery. Compared to WRF‐BACM, WRF‐UACM reduces the cold bias soon after sunset, thus improving the fog onset error by ∼3 hr. This study highlights the UACM's potential to improve fog prediction and its application in operational settings. With further investigation into different fog types, the UACM can provide crucial insights for preventive measures and reducing disruptions in urban areas.

Role of meteorology and air pollution on fog conditions over Delhi during the peak winter 2024

Severe air pollution and foggy conditions during winter are persistent challenges, pose significant health hazards, and disrupt daily routines worldwide. In this study, we have investigated the conditions favoring the prolonged fog events in Delhi during January 2024 using observations, back trajectories, and reanalysis datasets. Analysis of visibility observations reveals that foggy (54, 121, 139, and 372 half-hours of very dense, dense, moderate, and shallow fog, respectively) conditions persisted in Delhi for 46 % of the time during the study period. The existence of 3–4 days of cold wave to severe cold wave conditions and the lack of passage of strong western disturbances across north and northwest India have also favored the prolonged fog formation. In addition, high relative humidity (>80 %), shallow boundary layer (216 m), stable weather conditions such as the absence of significant surface winds, the existence of cold wave to severe cold wave, temperature inversion (up to 4 °C), poor ventilation, and presence of high particulate matter (PM10: 298 μg/m3 and PM2.5: 182 μg/m3) facilitated the fog formation. Further, analyses reveal a spurt in daily particulate matter (PM10: 603 μg/m3 and PM2.5: 420 μg/m3; 13.4 and 28 times, respectively, exceeded the WHO air quality guideline levels) along with 4.5 h of zero visibility on 14th January. The analysis of particulate matter reveals the dominance of fine particles from nearby regions, which could have originated from the large-scale anthropogenic open biomass burning used for heating activities. The results derived from this study indicate the need for an accurate representation of the local anthropogenic emissions in the atmospheric models to improve the predictability of air quality and fog and provide insights into the need for their control, particularly during such extreme events.

Hygroscopic growth and activation changed submicron aerosol composition and properties in the North China Plain

Abstract. Aerosol hygroscopic growth and activation under high-relative-humidity (RH) conditions significantly influence the physicochemical properties of submicron aerosols (PM1). However, this process remains poorly characterized due to limited measurements. To address this gap, we deployed an advanced aerosol–fog sampling system that automatically switched between PM1, PM2.5 and total suspended particulate (TSP) inlets at a rural site in the North China Plain in the cold season. The results revealed that aerosol swelling due to water vapor uptake influenced aerosol sampling under high-RH conditions by shifting the cut-off size of impactors. At subsaturated high RH (> 90 %), over 25 % of aerosol mass with dry diameters below 1 µm resided in supermicron ranges, while in supersaturated foggy conditions, more than 70 % of submicron aerosol migrated to supermicron ranges. Hygroscopic growth and activation particularly affected highly hydrophilic inorganic salts, shifting a significant number of submicron sulfate and nitrate particles to supermicron ranges, with 27 %–33 % at 95 % ≤ RH ≤ 99 % and more than 78 % under supersaturated foggy conditions. Moreover, more than 10 % of submicron biomass burning organic aerosols grew beyond 2.5 µm during fog events, while fossil-fuel-related organic aerosol (FFOA) remained dominantly in submicron ranges, suggesting inefficient aqueous conversion of FFOA. The two secondary organic aerosol (SOA) factors (OOA1 and OOA2) behaved differently under supersaturated conditions, with OOA2 exhibiting a higher activated fraction despite a lower oxygen / carbon ratio. A substantial increase in organic nitrate and organosulfur mass concentrations in activated droplets during fog events suggested aqueous conversions and formations of brown carbon with potential radiative impacts. Overall, our study highlights remarkably different cloud and fog processing behaviors between primary and secondary aerosols, which would benefit a better understanding of aerosol–cloud interactions under distinct atmospheric conditions.

Immunocytochemical evaluation of aquaporins and cell wall components and their influence on foliar water uptake in Andean Melastomataceae.

Andean ecosystems are characterized by high humidity, mainly from rain and fog events. Because of differences in altitude two Andean ecosystems - sub-Andean forest and Páramo -face different environmental pressures that affect leaf anatomy and cell wall composition and, consequently, species foliar water uptake (FWU) capacity. Here, FWU capacity of eight species in the Melastomataceae was evaluated and found to be related to proportions of cell wall components and aquaporins in the two ecosystems. Cellulose was labelled with Calcofluor white, and aquaporin and pectins were labelled with monoclonal antibodies. There were differences in plant FWU capacity in both ecosystems, with higher FWU capacity in sub-Andean forest species than in Páramo forest species. Cell wall components were positively related to FWU, with increased FWU related to pectin and aquaporin content of the plasma membrane. Differences in water availability in the two analysed environments led to differences in FWU capacity that are associated with leaf anatomical traits and cell wall composition. In these two environments, plants with similar traits are selected to respond to given environmental pressures. Traits that favour FWU in sub-Andean forest species may lead to further advances of these species in this environments.

Nighttime agglomerate fog event detection considering car light glare based on video

Agglomerate fog event poses more serious threat than normal foggy weather to expressway traffic safety, due to its localized nature and suddenly uneven formation. However, vision-based fog detection methods typically estimate visibility for individual images and ignore the difference in the characteristics of even and uneven fog, lacking use of temporal information to differentiate between normal foggy weather and agglomerate fog events. Meanwhile, detection of fog at night faces strong interference from car lights that is always overlooked. This study proposes a nighttime agglomerate fog event detection method for videos, taking into account car light interference. Depth disparity feature is constructed based on the information entropy of depth estimation result, and in order to build a metric for uneven characteristics in the field of view, we creatively introduce the Moran’s index to establish uneven feature, generating two-dimensional feature time series for each video. By extracting interpretable features from the two-dimensional feature time series after removing car light interference frames, a classification model based on XGBoost is built to differentiate agglomerate fog, normal fog, and no fog videos. Experiments are carried out utilizing real monitoring data from roadside surveillance cameras to validate the effectiveness of features and model. Furthermore, a fog event detection dataset containing over 1500 videos is established, making up data scarcity for vision-based agglomerate fog event detection and providing support for future research.

Impact of Assimilating Uncrewed Aircraft System Observations on River Valley Fog Prediction

Abstract The impact of assimilating targeted Uncrewed Aircraft System (UAS) observations on the prediction of radiation and river-valley fog is assessed using Observing System Experiments (OSEs). Multi-rotor UAS were deployed during FOGMAP (Frequent in situ Observations Above Ground for Modeling and Advanced Prediction of fog) which took place during the summer of 2022 in northern Kentucky. Targeted UAS missions were flown to sample the spatio-temporal variability of temperature and moisture in the vicinity of the Cincinnati/Northern Kentucky International Airport. During each mission the UAS performed near-continuous profiling at two locations between the surface to 120 m AGL throughout the night. Data denial experiments were performed using the Ensemble Kalman Adjustment Filter available in NSF NCAR’s Data Assimilation Research Testbed (DART) to determine the impact of assimilating UAS observations on the skill of analyses and forecasts issued during potential fog events. Simulations that only assimilated conventional observations tended to have a dry bias in the analyses and forecasts. The dry bias in the analyses was reduced in experiments that assimilated UAS observations leading to improved probabilistic predictions of fog. Sensitivity tests revealed that the ensemble mean analyses were improved when assimilating UAS observations of specific humidity rather than relative humidity (RH) due to the existence of a cold bias near the surface and the negative covariance between RH and temperature. It was also found that either the assumed observation error variance of (1 g kg−1)2 or the ensemble spread of the background specific humidity was too large since their sum tended to overestimate the Root Mean Squared Error (RMSE) of the predicted ensemble mean values.

Multi-process atmospheric particle number size distribution over the Bohai Sea: Insights from cruise and onboard unmanned aerial vehicle observations

A better understanding of the particle number size distribution aids to better assess the direct and indirect effects of particles on air quality and climate. In this study, particle number concentrations (PNCs) and size distribution along with chemical components, gaseous pollutants, and meteorological parameters were measured during a cruise campaign over the Bohai Sea. Four distinct periods were identified, showing significant impacts from continental outflows and ocean emissions on the particle number size distributions. Under the strong terrestrial pollution transport period, an obvious increase of PNCs below 1 μm was observed. The significant correlation between black carbon (BC) and PNCs in the size range of 0.35–1.0 μm suggested aging of aerosols during the long-range transport. An invaded dust pollution significantly reduced PNCs below 0.5 μm, while tripled the number concentration of particles larger than 0.5 μm. The ocean moisture facilitated the mixing between dust and secondary aerosols. An intense sea fog event observed during the cruise slightly increased PNCs smaller than 1 μm while decreasing larger ones. The correlations between PNCs below 0.5 μm and BC as well as SO2 demonstrated the impact of shipping activities on the formation of fresh particles. Aerosol vertical profiles in the marine boundary layer were measured by an unmanned aerial vehicle platform. The vertical patterns of particle number size distribution were largely governed by the origins of transported air masses and profiles of wind fields. Observations showed that the particle distribution in the lower marine boundary layer was typically inhomogeneous and rapidly evolving with time, highlighting the importance of strengthening the vertical observations of atmospheric parameters over the ocean.

THE ROLE OF AIR TEMPERATURE AND DEW POINT DURING FOG RECURRENCES ON THE ABSHERON PENINSULA (AZERBAIJAN)

The article focuses on the characteristics of air temperature and dew point changes observed during repeated fog events in the Absheron Peninsula in 2000...2022. For this purpose, continuous observation data of Heydar Aliyev International Airport was used. Here is an analysis of all types of fog by month of occurrence. The limits of total fog, Meteorological Optical Range ≤ 500 m. and 501...1000 m. are considered in the analysis. Repeating such criteria, attention was paid to the recorded air temperature and dew point indicators for I...III, IV...VI and X...XII months of the year. The analyzes show that the fogs observed in the peninsula are mostly recorded at a temperature of 6...8 0C. The most commonly observed dew point temperature ranges of 0,0...0,3 0C and 1,0...1,2 0C at all ranges of MOR in fog repeats. The results of the research are of particular importance for the planning of the work of all transport areas and the forecast of fogs.

London Fog: A Century of Pollution and Mortality, 1866–1965

Abstract This study draws on London’s long experience with air pollution in order to improve our understanding of the overall effects of pollution exposure and how and why these effects evolve as locations develop. I compare uniquely detailed new mortality data covering 1866 to 1965 to the timing of London’s famous fog events, which trapped emissions in the city. I show that air pollution was a major contributor to mortality in London over this period and that it interacted strongly with specific infectious diseases. As a consequence of this interaction, reductions in the infectious disease burden substantially altered the health costs of pollution.

Short‐Term Sea Fog Area Forecast: A New Data Set and Deep Learning Approach

AbstractPrompt and precise forecast of sea fog regions ensures maritime navigational safety. This paper establishes a prompt and precise forecast of sea fog regions that ensure maritime navigational safety. This paper establishes a multivariable sea fog forecast (MV‐SFF) data set and proposes a deep learning‐based forecast method named rich‐element aggregated (REA) for short‐term forecasts. The MV‐SFF data set contains 122 sea fog events from 2010 to 2020. Each event in the MV‐SFF data set includes meteorological variables from reanalysis data and geostationary ocean color imager satellite images captured hourly on the day of the sea fog occurrence. This data set aims to comprehensively utilize meteorological elements and remote sensing observations to predict the spatial changes of sea fog areas in the next 7 hours. The proposed REA model can extract and integrate features from historical meteorological elements of different types, times, and spatial locations. In addition, REA utilizes a position‐aware edge detection mechanism to locate the exact position of sea fog. We perform a seven‐hour ahead forecast starting from 09:16 local time and show promising forecasting results, which demonstrate the fog area forecast ability of our model. Compared with existing advanced deep learning networks, the REA model is superior in performance and stability.

The role of topography on the local circulation and formation of fog at Perth Airport

Perth Airport is located on a coastal plain in the south-west of Australia, with the Indian Ocean to the west and the Darling Scarp running approximately parallel to the coast to the east. On average, there are approximately nine fog events per year at the airport, typically occurring during the cooler months in the early morning hours. Onshore winds bringing moisture from the Indian Ocean can combine with nocturnal cooling in stable atmospheres to encourage fog formation. A previous climatological study of fog at Perth Airport found that the majority of events had north to north-easterly 10-m winds at fog onset time. Two case studies are presented to gain a better understanding of the physical processes associated with the north to north-easterly near-surface flow and their influence on the development of fog. The hypothesis is that the escarpment is blocking the moist environmental flow, resulting in light northerly near-surface winds. This was tested through numerical experiments including altered terrain. The main finding from the case studies was that the northerly winds stem from a blocking of the airmass in the lower level of the atmosphere by the Darling Scarp in moderate wind situations. During calm or very light wind occasions, the winds below the surface inversion level can tend northerly regardless of topography. The trapped airmass and light winds in the near surface layer in combination with nocturnal surface cooling and moisture from the environmental flow, create conditions favourable for the development of fog at Perth Airport.

A mechanism for coastal fog genesis at evening transition

AbstractTransitional changes in the atmospheric boundary layer (ABL) are known to facilitate the onset of terrestrial fog, which is defined as a condition with near‐surface visibility <1 km due to airborne water droplets. In particular, the evening transition from a daytime convective ABL to a night‐time stable ABL provides favorable conditions for fog. This article describes a local fog event observed during the evening transition at a Canadian islet in the north Atlantic known as Sable Island during the “Fog and Turbulence Interactions in the Marine Atmosphere (Fatima)” field campaign. The comprehensive set of data collected using a myriad of instruments covering a wide range of scales allowed identification of a novel mechanism underlying this fog event. Therein an ocean–land discontinuity created a flow regime consisting of several stacked boundary layers, interplay of which produced a thin low‐level cloud that then diffused downward to the surface, causing visibility reduction. This mechanism offers useful insights on the role of boundary layers, stratification, and turbulence in fog genesis over oceanic islands.

Sulfate Formation Driven by Wintertime Fog Processing and a Hydroxymethanesulfonate Complex With Iron: Observations From Single‐Particle Measurements in Hong Kong

AbstractFog processing has a significant impact on sulfur chemistry in the atmosphere. This study analyzed three winter fog events in Hong Kong using single‐particle aerosol mass spectrometry (SPAMS) and a Monitor for AeRosols and GAses in ambient air (MARGA). Black carbon (BC)‐related carbonaceous particles with substantial sulfate amounts comprised the largest particle number fraction (56.7%). Sulfate mass concentration decreased during fog due to the cloud's effective scavenging, but fog processing notably promoted sulfate formation at the single‐particle level (average peak area increases of 31.2%). Hydroxymethanesulfonate (HMS), an important S(IV) compound and fog tracer, was identified accounting for up to 12% by particle number fraction. Although pH showed a positive correlation (r = 0.53–0.69) with HMS particles in each fog scenario, a negative overall correlation (r = −0.51) was observed. Further analysis revealed that the higher aerosol acidity (pH 0.65–3.11), promoted Fe dissolution, leading to 49% of HMS particles being mixed with Fe, which potentially facilitated sulfate formation via the Fenton reaction. Additionally, around 40% of HMS‐Fe particles are mixed with oxalate, thereby warranting further attention for their potential to cause more intricate sulfur oxidation processes. This study reveals the initial identification of a high mixed‐state of HMS‐Fe, which could potentially serve as a crucial avenue for the formation of sulfate on individual particulate matter. Considering the persistent augmentation of aerosol acidity in the Asian region, this phenomenon necessitates further investigation and attention.

Dense Fog in the Netherlands: Composition of the Nuclei that Contribute Most to the Droplet Number Concentration

Dense fogs, with a visibility of less than 200 m, form a traffic hazard. Usually, models describing their formation use observations at the Cabauw super-site in the Netherlands for evaluation. A key parameter is the number of fog droplets and thus the number of aerosol particles on which the fog droplets form, the so-called fog nuclei (FN). No observational data are available for this key microphysical feature. An assumption is that this number scales with the concentration of the hygroscopic aerosol component sulfate. However, in the Netherlands nitrate and organics are the more important components of the total aerosol and thus possibly also of the FN. This short communication provides the first actual data via measurements with an aerosol mass spectrometer—AMS—for a period with dense fog events observed in November 2011. The aerosol in the relevant size range was composed of about half of the hygroscopic ammonium nitrate/sulfate. The other half consisted of organics; the low O/C ratio indicated that these compounds are rather hydrophobic; the hygroscopicity factor kappa of this mix was estimated at 0.3. This value implies that the activation diameter (the lowest diameter of the FN) was at least 150 nm. The mass distribution was converted into a number distribution which showed a sharp decrease as a function of size for diameters above this threshold. This result implies that the vast majority of the FN have diameters to the activation diameter. These smallest FN contained ammonium nitrate as the major hygroscopic compound. Currently, data for other dense fogs are evaluated to search for a possible generality of this finding.

An Observational Case Study of a Radiation Fog Event

A micrometeorological fog experiment was carried out in Budapest, Hungary during the winter half year of 2020–2021. The field observation involved (i) standard meteorological and radiosonde measurements; (ii) surface radiation balance and energy budget components, and (iii) ceilometer measurements. 23 fog events occurred during the whole campaign. Foggy events were categorized based on two different methods suggested by Tardif and Rasmussen (2007) and Lin et al. (2022). Using the Present Weather Detector and Visibility sensor (PWD12), duration of foggy periods are approximately shorter (~ 9%) compared to ceilometer measurements. The categorization of fog based on two different methods suggests that duration of radiation fogs is lower compared to that of cloud base lowering (CBL) fogs. The results of analysis of observed data about the longest fog event suggest that (i) it was a radiation fog that developed from the surface upwards with condition of a near neutral temperature profile. Near the surface the turbulent kinetic energy and turbulent momentum fluxes remained smaller than 0.4 m2 s–2 and 0.06 kg m–1 s–2, respectively. In the surface layer the vertical profile of the sensible heat flux was near constant (it changes with height ~ 10%), and during the evolution of the fog, its maximum value was smaller than 25 W m–2, (ii) the dissipation of the fog occurred due to increase of turbulence, (iii) longwave energy budget was close to zero during fog, and a significant increase of virtual potential temperature with height was observed before fog onset. The complete dataset gives an opportunity to quantify local effects, such as tracking the effect of strengthening of wind for modification of stability, surface layer profiles and visibility. Fog formation, development and dissipation are quantified based on the micrometeorological observations performed in suburb area of Budapest, providing a processing algorithm for investigating various fog events for synoptic analysis and for optimization of numerical model parameterizations.

Effects of surface moisture flux on the formation and evolution of cold fog over complex terrain with large‐eddy simulation

AbstractThis study examines the effect of surface moisture flux on fog formation, as it is an essential factor of water vapor distribution that supports fog formation. A one‐way nested large‐eddy simulation embedded in the mesoscale community Weather Research and Forecasting model is used to examine the effect of surface moisture flux on a cold fog event over the Heber Valley on January 16, 2015. Results indicate that large‐eddy simulation successfully reproduces the fog over the mountainous valley, with turbulent mixing of the fog aloft in the valley downward. However, the simulated fog is too dense and has higher humidity, a larger mean surface moisture flux, more extensive liquid water content, and longer duration relative to the observations. The sensitivity of fog simulations to surface moisture flux is then examined. Results indicate that reduction of surface moisture flux leads to fog with a shorter duration and a lower height extension than the original simulation, as the decrease in surface moisture flux impairs water vapor transport from the surface. Consequently, the lower humidity combined with the cold air helps the model reproduce a realistic thin fog close to the observations. The outcomes of this study illustrate that a minor change in moisture flux can have a significant impact on the formation and evolution of fog events over complex terrain, even during the winter when moisture flux is typically very weak.

Electrical measurements during fog in the United Arab Emirates

Distinct differences in electrical characteristics of the atmosphere are observed during clear and foggy laden air. The presence of droplets in the air causes the removal of natural cluster ions and hence, a change in the electrical properties, which is useful for fog detection, and potentially fog forecasting. In this study, we report on some of the first electrical measurements conducted during fog in the United Arab Emirates (UAE).The analysis indicates that the Potential Gradient (PG) values observed during fog in the UAE were substantially higher than those previously reported in the literature (ranging from −1247 V/m to 1400 V/m). Furthermore, the PG during fog was often negative, with 93% of cases recording negative PG values (with median PG value of −397 V/m), particularly during wintertime fog events. A comparison with fog measurements conducted in the UK showed a stark contrast in PG behaviour between the two sites, with only positive PG values reported during fog in the UK (as is the case for the majority of PG fog studies reported in the literature), and higher PG variability in the UAE fogs. It is hypothesized that the unusual polarity of PG observed in UAE fog events may be attributed to the deposition of fog droplets, during which positive charges are transported from the top of the fog layer downwards towards the surface, thereby modifying PG. This deposition process is expected to be particularly active during the latter stages of the fog, when the droplet size distribution has fully evolved.

Different Mechanisms for the Northern and Southern Winter Fog Events over Eastern China

Northern and southern fog events are identified over eastern China across 40 winters from 1981 to 2021. By performing composite analysis on these events, this study reveals that the formation of fog events is controlled by both dynamic and thermodynamic processes. The fog events were induced by Rossby wave trains over the Eurasian continent, leading to the development of surface wind and pressure anomalies, which favor the formation of fog events. The Rossby wave trains in northern and southern fog events are characterized by their occurrence in northern and southern locations, respectively, with different strengths. The water vapor fluxes that contribute to the enhancement of the northern fog events originate from the Yellow Sea and the East China Sea, whereas the southern fog events are characterized by water vapor from the East China Sea and the South China Sea. In both northern and southern fog events, dew point depression and positive A and K index anomalies are found in northern and southern regions of eastern China, which are indicative of supersaturated air and the unstable atmospheric saturation from the low to the middle troposphere, thus providing favorable conditions for the establishment of fog events in northern and southern regions of eastern China.

Numerical prediction of fog: A novel parameterization for droplet formation

AbstractA novel aerosol activation scheme was developed and implemented into the WRF Thompson–Eidhammer Aerosol‐Aware microphysical module. While in most of the numerical weather prediction (NWP) models the activation is based on updraft velocity, even in the fog, the new parameterization considers the local rate of cooling and water vapor flux in the evaluation of the aerosol activation rate. In addition, diagnostic variables are added to evaluate the visibility reduction due to formation of haze droplets. The impact of changing the activation scheme is demonstrated by a case study of a well‐observed fog event. Data observed during the fog event campaign at Budapest and observed at standard meteorological stations are compared with the output of the numerical model. The results are summarized as follows: (i) the inhomogeneous spatial and temporal distribution of the number concentration of droplets is an inherent characteristic of the new parameterization scheme. (ii) Compared to the prior parameterization based on updraft velocity, the new parameterization scheme increases the number concentration of the droplets significantly, especially at the top of the fog. As a consequence, it reduces the downward short‐wave radiation flux prolonging the lifetime of the fog by about 30–60 min. (iii) Analyses reveal that earlier dissipation of the fog comparing to the observed data cannot be explained only by overestimation of the downward short‐wave radiation flux. (iv) The new method is able to evaluate the reduction of visibility due to haze.