Foggy Conditions Research Articles

Temporal Variations of PM2.5, PM10, and Gaseous Precursors during the 1995 Integrated Monitoring Study in Central California

ABSTRACT The spatial and temporal distributions of particle mass and its chemical constituents are essential for understanding the source-receptor relationships as well as the chemical, physical, and meteorological processes that result in elevated particulate concentrations in California’s San Joaquin Valley (SJV). Fine particulate matter (PM2.5), coarse particulate matter (PM10), and aerosol precursor gases were sampled on a 3-hr time base at two urban (Bakersfield and Fresno) and two non-urban (Kern Wildlife Refuge and Chowchilla) core sites in the SJV during the winter of 1995–1996. Day-to-day variations of PM2.5 and PM10 and their chemical constituents were influenced by the synoptic-scale meteorology and were coherent among the four core sites. Under non-rainy conditions, similar diurnal variations of PM2.5 and coarse aerosol were found at the two urban sites, with concentrations peaking during the nighttime hours. Conversely, PM2.5 and coarse aerosol peaked during the morning and afternoon hours at the two non-urban sites. Under rainy and foggy conditions, these diurnal patterns were absent or greatly suppressed. In the urban areas, elevated concentrations of primary pollutants (e.g., organic and elemental carbons) during the late afternoon and nighttime hours reflected the impact from residential wood combustion and motor vehicle exhaust. During the daytime, these concentrations decreased as the mixed layer deepened. Increases of secondary nitrate and sulfate concentrations were found during the daylight hours as a result of photochemical reactions. At the non-urban sites, the same increases in secondary aerosol concentrations occurred during the daylight hours but with a discernable lag time. Concentrations of the primary pollutants also increased at the non-urban sites during the daytime. These observations are attributed to mixing aloft of primary aerosols and secondary precursor gases in urban areas followed by rapid transport aloft to non-urban areas coupled with photochemical conversion.

A method for identifying sulfuric acid in single cloud and fog droplets

We describe herein a novel method for identifying sulfuric acid in single droplets of mist, fog or cloud. The method is based on a microchemical reaction displayed by the droplets upon a shiny cleavage plane [ 1 0 1 1 ̄ ] of Iceland spar – the rhombohedral variety of calcite. Thus, single droplets containing sulfuric acid respond by a typical microchemical reaction wherein they create prismatic, hemi-bipyramidal or lenticular twinned gypsum crystals on the calcite surface. For acid identification, droplets were collected on the four stages of a cascade impactor. The method was tested both in the laboratory and in the field in cloudy and foggy conditions. The sulfur mass in single droplets varied between 10 −12 and 10 −13 g and the pH ranged from 2.0 to 4.0.

Mis(t) information

Drivers in foggy conditions are frequently involved in accidents and are often `blamed' for driving too fast for the weather conditions. But are these accidents solely caused by the recklessness of the drivers or are there other reasons? Clearly, when attempting to judge one's speed during reduced visibility one is less likely to look away from the road to the speedometer as this might cause an accident in itself. This places an additional burden on the perceptual systems that can also provide clues to speed. Snowden et al., 1998[1xSpeed perception fogs up as visibility drops. Snowden, R.J., Stimpson, N., and Ruddle, R.A. Nature. 1998; 392: 450Crossref | PubMed | Scopus (82)See all References][1]have recently examined the ability of drivers to adjust their speed in a virtual environment that simulated the view from a car moving along a road. In one experiment they showed subjects two driving scenes, one with clear weather, the other with either clear or reduced visibility and calculated the speed at which the subjects reported that the two scenes appeared to be moving at the same speed. The results indicated that drivers perceived the foggy scene to be moving more slowly than the clear scene. In a second experiment the subjects were asked to try to match their speed to a target speed in a variety of weather conditions in a more realistic driving simulator involving a winding road, a steering wheel, and brake and accelerator pedals. Again, as the weather condition deteriorated the subjects drove faster. These results raise the question of the role of our perceptual systems in driver irresponsibility under poor visibility and may provide a test-bed for novel approaches to this problem.

霧中を伝搬するレーザ送信ビームの広がりの伝達関数の測定とその伝達関数を用いたビーム伝搬解析

In a past study, we developed a laser radar system for estimating slant visibility, which is the visibility along the glide path of an airplane and proposed the new laser radar equation, considering the divergence of the transmitting laser beam in bad weather conditions, like rain, fog and snow, in order to obtain the exact slant visibility in various weather conditions. This equation corresponds well to practical data and estimated visibilities coincide well with actual ones in various weather conditions.In the present study, to confirm the appropriateness of the new laser radar equation, the scattering angle characteristics of a laser beam propagating through fog is measured by using an optical Fourier transform system and an artificial fog generator. As a result of this experiment, the spatial spread functions of broadening of the forward beam caused by the fog scattering are derived from the obtained data as angle distribution.Using these spread functions, the analysis of broadening of a laser beam propagating through fog in laser radar operation using a computer. This computer analysis reveals the alternation of the pattern of the transmitting laser beam through fog. As a result, broadening and scattering characteristics of the transmitting beam in foggy condition were found and the spreads of transmitting beam derived from the calculated results well explain the concept of the new equation.The analyzed results compared well with practical data for laser radar. And the slant visibilities derived from the analyses well coincided the actual ones.

愛媛県大洲に発生する盆地霧の気候学的な特徴

The Ohzu Basin is located in the north western part of Shikoku Island as is shown in Fig. 1. As in other basins in Japan, basin fog appears frequently from autumn to winter. In order to make clear the climatological characteristics of basin fog at the Ohzu Basin, Ehime prefecture, and understand its role as an element of agro-climatological resources, observations were carried out from Sep. 8, 1995 to Feb. 5, 1996. The sites were located at bottom of the basin and on mountainside faced to the center of the basin. The latter site was situated above the upper surface of the fog layer which appears typically in the Ohzu Basin. Spatial distribution of the fog were also analyzed using the LANDSAT images provided on Dec. 5, 1985 and Dec. 13, 1988.The results obtained in this study were summarized as follows:(1) The total number of fog day reached 46 days during the present observation period mentioned above. In the most frequent period, fog occurred at the ratio of one day to two day in October and November.(2) Dispersion time of the fog changed seasonally accordance with a shift of time of sunrise, and the fog has lasted 4 hours or more after the sunrise under dominant foggy conditions.(3) The meteorological characteristics of foggy day were shown as follow, attenuated of solar radiation in the morning, decreased of radiative cooling in nighttime, and low temperature until fog dissipate.(4) Several % of monthly total solar radiation was shaded by fog layer at the basin bottom site. Total time of saturation condition indicated by R.H.=100% on foggy days became 21 hours at the site of mountain slope. At the basin bottom site, it reached 493 hours during the period of the observation.(5) Upper surface of the fog layer was limited to a height about 300m above the sea level, and distributed horizontally along lower part of the Hiji River. The maximum height was affected by the surrounding topography.(6) In the Ohzu Basin, hamlets on the mountain slope distributed zonally above the fog layer. This indicates that the fog has a remarkable influence on human life of mountainous region. On the other hand, the chinese cabbage-producing district was formed in the foggy area. Utilizing this foggy climate of the basin, high quality chinese cabbage with soft leave are produced in the basin bottom.

Fog droplets—an atmospheric source of secondary biological aerosol particles

The occurrence of airborne biological particles (bacteria, yeasts and moulds) in fog water and the influence of temperature and fog chemical composition and acidity on their concentration are described in this paper. Our results show that the concentration of airborne bacteria and yeasts is enriched in foggy conditions up to two orders of magnitude compared to clear air conditions, while concentration of moulds is not influenced by the presence of fog. These results support the hypothesis that fog droplets act as culture media for airborne biological particles, i.e. they represent an atmospheric source of secondary biological particles.

Environmental genotoxicity and cancer risk in humans

It is well documented that environmental pollution from industrial activity, sewage farms, hazardous waste sites, incinerators, etc, contributes to the overall cancer risk and that this contribution can be considerable under certain circumstances. It is important, therefore, to identify the level of genotoxic activity in the environment and to relate it to biomarkers of cancer risk in humans. After reviewing a range of cytogenetic assays, we have selected the Tradescantia micronucleus assay (TRAD-MCN) developed by Ma et al to be used in indoor and field evaluations. The meiotic pollen mother cells of T clone 4430 are particularly sensitive to chemical pollutants; the buds are exposed for 6-8 h. We describe assays made down wind from a coal-fired power station and from the vicinity of two waste sites. Statistically significant results were obtained at 200 m and 600 m down wind from the power station; higher levels of micronucleus frequencies (MN) were found in foggy rather than dry conditions. Similarly, in the vicinity of two waste sites the MN frequencies were significantly increased in both dry and foggy conditions up to 1.5 km down wind; this was despite previous efforts to rehabilitate the sites. The TRAD-MCN assay is sensitive, reproducible, easy to perform, well standardized, inexpensive and undemanding in equipment. We propose that it be the primary test for genotoxicity evaluation and mapping followed, in suspicious areas, by human biomarker assays.

Tether corrections for tethered balloon wind measurements

When the deflection of a tethered spherical balloon from the vertical is used to measure the strength and direction of a light low-level wind, the gravity and wind drag forces on the tether may have a significant influence, producing a curvature in the tether and changing the direction of its pull on the balloon. A technique has been developed for accurately calculating the effect of these forces. The measurements required for the technique are the free lift of the balloon, the length, diameter, and weight of the tether, and either the orientation of the balloon from the ground tether point (the generally preferred method), or the orientation of the tether near the ground (appropriate in foggy conditions). Some examples are given which indicate the conditions under which the forces on the tether are important, and some measurements are set out which show that the technique gives good results.

Modification of the aerosol content and chemical effects induced by vegetation under high electric field condition

The paper deals with results from a measuring campaign in the nature and from a laboratory study. It was observed that high electric fields occur not only during thunderstorms and foggy conditions but sometimes also by fair weather. In electrical terms, it means that gaseous corona discharges can be produced in all these cases at the top of pointed trees with the high-pressure low-temperature plasmas characteristics, i.e. in particular with the production of gaseous O 3 , NO 2 − , NO 3 − , SO 4 2− and particules in the submicronic range due to gaz-to-particule conversion, but also with the emission of larger droplets containing vegetal components, such as solvated Cl − , NO 3 − and oxidized organic species, as observed in the laboratory study. So, it seems that both the chemical composition and the aerosol content can be influenced by the electrodynamical characteristics of the lower atmosphere.

An Expert System Approach for Prediction of Maritime Visibility Obscuration

Abstract An Expert system for Shipboard Obscuration Prediction (AESOP), an artificial intelligence approach to forecasting maritime visibility obscurations, has been designed, developed, and tested. The problem-solving model for AESOP, running within an IBM-PC environment, is rule-based, uses backward chaining, and has meta-rules; a user, in a consultation session, answers questions about certain atmospheric parameters. The current version, AESOP 2.0, has 232 rules and has been designed in terms of nowcasts (0–1 h) and forecasts (1–6 h). An extensive explanation feature allows the user to understand the reasoning process behind a particular forecast. AESOP has been evaluated against 83 test cases, in which clear, hazy, or foggy conditions are predicted. The overall performance of AESOP is 75% correct. This value indicates considerable forecast skill when compared to 47% for persistence and 41% for random chance. When the distinction between clear and haze is ignored, the expert system correctly forecasts ...

Acid Fog: Effects on Respiratory Function and Symptoms in Healthy and Asthmatic Volunteers

Acidic air pollutants generally are dissolved in water droplets. Mean droplet diameter may range from more than 10 microns in dense fog to less than 1 micron at low relative humidity. Droplet size influences the deposition of inhaled acid within the respiratory tract and thus may influence toxicity. To help assess health risks from acid pollution, we performed controlled exposures of normal and asthmatic volunteers to sulfuric acid aerosols at nominal concentrations of 0 (control), 500, 1000, and 2000 micrograms/m3. Exposures lasted 1 hr with intermittent heavy exercise. Response was assessed by lung function tests and symptom questionnaires. Under foggy conditions (mean droplet size 10 microns, temperature 50 degrees F), no marked effects on lung function were found. However, both normal and asthmatic subjects showed statistically significant dose-related increases in respiratory symptoms. In a separate study, normal subjects exposed at 70 degrees F with mean droplet size 0.9 microns showed no marked effect on function or symptoms. Asthmatics showed dose-related decrements in forced expiratory performance and increases in symptoms, most obvious at 1000 and 2000 micrograms/m3. The different results of the two studies probably reflect an influence of droplet size, but further investigation is needed to confirm this. The aggregate results suggest that only mild, if any, short-term respiratory irritant effects are likely at acid concentrations attained in ambient pollution.

Acid fog: effects on respiratory function and symptoms in healthy and asthmatic volunteers.

Acidic air pollutants generally are dissolved in water droplets. Mean droplet diameter may range from more than 10 microns in dense fog to less than 1 micron at low relative humidity. Droplet size influences the deposition of inhaled acid within the respiratory tract and thus may influence toxicity. To help assess health risks from acid pollution, we performed controlled exposures of normal and asthmatic volunteers to sulfuric acid aerosols at nominal concentrations of 0 (control), 500, 1000, and 2000 micrograms/m3. Exposures lasted 1 hr with intermittent heavy exercise. Response was assessed by lung function tests and symptom questionnaires. Under foggy conditions (mean droplet size 10 microns, temperature 50 degrees F), no marked effects on lung function were found. However, both normal and asthmatic subjects showed statistically significant dose-related increases in respiratory symptoms. In a separate study, normal subjects exposed at 70 degrees F with mean droplet size 0.9 microns showed no marked effect on function or symptoms. Asthmatics showed dose-related decrements in forced expiratory performance and increases in symptoms, most obvious at 1000 and 2000 micrograms/m3. The different results of the two studies probably reflect an influence of droplet size, but further investigation is needed to confirm this. The aggregate results suggest that only mild, if any, short-term respiratory irritant effects are likely at acid concentrations attained in ambient pollution.

Potential Risks to Human Respiratory Health from "Acid Fog": Evidence from Experimental Studies of Volunteers

Observations of high acidity (pH as low as 1.7) in fogwater collected in polluted areas have provoked concern for public health. Effects of exposure to acidic pollutants have not been studied under foggy conditions; thus there is no directly relevant information from which to estimate the health risk. Indirectly relevant information is available from numerous studies of volunteers exposed to "acid fog precursors" under controlled conditions at less than 100% relative humidity. The effect of fog in modifying responses to inhaled acidic pollutants is difficult to predict: depending on circumstances, fog droplets might either increase or decrease the effective dose of pollutants to the lower respiratory tract. Fog inhalation per se may have unfavorable effects in some individuals. Sulfur dioxide is known to exacerbate airway constriction in exercising asthmatics, at exposure concentrations attainable in ambient air. Nitrogen dioxide has shown little untoward respiratory effect at ambient concentrations in most studies, although it has been suggested to increase bronchial reactivity. Sulfuric acid aerosol has shown no clear effects at concentrations within the ambient range. At somewhat higher levels, increased bronchial reactivity and change in mucociliary clearance have been suggested. Almost no information is available concerning nitric acid.

Potential risks to human respiratory health from "acid fog": evidence from experimental studies of volunteers.

Observations of high acidity (pH as low as 1.7) in fogwater collected in polluted areas have provoked concern for public health. Effects of exposure to acidic pollutants have not been studied under foggy conditions; thus there is no directly relevant information from which to estimate the health risk. Indirectly relevant information is available from numerous studies of volunteers exposed to "acid fog precursors" under controlled conditions at less than 100% relative humidity. The effect of fog in modifying responses to inhaled acidic pollutants is difficult to predict: depending on circumstances, fog droplets might either increase or decrease the effective dose of pollutants to the lower respiratory tract. Fog inhalation per se may have unfavorable effects in some individuals. Sulfur dioxide is known to exacerbate airway constriction in exercising asthmatics, at exposure concentrations attainable in ambient air. Nitrogen dioxide has shown little untoward respiratory effect at ambient concentrations in most studies, although it has been suggested to increase bronchial reactivity. Sulfuric acid aerosol has shown no clear effects at concentrations within the ambient range. At somewhat higher levels, increased bronchial reactivity and change in mucociliary clearance have been suggested. Almost no information is available concerning nitric acid.

Thermal vegetation canopy model studies

An iterative-type thermal model applicable to forest canopies was tested with data from two diverse forest types. The model framework consists of a system of steady-state energy budget equations describing the interactions of short- and long-wave radiation within three horizontally infinite canopy layers. A state-space formulation of the energy dynamics within the canopy is used which permits a factorization of canopy geometrical parameters from canopy optical and thermal coefficients as well as environmental driving variables. Two sets of data characterizing a coniferous (Douglas-fir) and deciduous (oak-hickory) canopy were collected to evaluate the thermal model. The results show that the model approximates measured mean canopy temperatures to within 2°C for relatively clear weather conditions and deviates by a maximum of 3°C for very hazy or foggy conditions.

Atmospheric levels of trace elements in Glasgow

Although the levels of atmospheric elements in Glasgow vary considerably throughout the year, the mean values are in general agreement with those recorded for similar environments throughout the world. Periods of fog and calm tend to increase levels, while rain clears the atmosphere. This has obvious implications for the setting of control standards for levels of elements in the atmosphere. Elemental levels are generally higher in winter with the exception of Se which reached a peak in summer. The trends for the other volatile element studied (Sb) were complicated by very high values recorded during foggy conditions. From a study of enrichment factors compared to soil or rock, it would appear that the major source of most of the elements present in the atmosphere is from the burning of fossil fuel with additional sources for Ag, Br, Sb, Se and Zn.

Some Stratus/Fog Statistics in Contrasting Coastal Plant Communities of California

Coast redwood (Sequoia sempervirens) distribution and foggy conditions are causally linked by some authors. Others suggest fog is of little importance to the distribution of coast redwood because stratus, not fog, is more typical of weather conditions in these areas. Limitedfog/stratus data from adjacent northern Californian areas with and without redwood are compared in this paper. Areas with redwood had more frequent early morning and early season stratus cover, but the frequency range within the redwood zone was substantial; fog was infrequent in both areas. This suggests that fog/stratus may not serve as a dominant factor for redwood distribution.

Lidar for routine meteorological observations

Lidar, using pulsed lasers as energy sources, applies the radar principle at wavelengths in and near the visual spectrum to probe the atmosphere. It can detect particulate matter of much smaller dimensions and sparser concentration than is possible with meteorological radar. Lidar may be used to measure cloud base heights although difficulties arise with diffuse clouds, especially in foggy conditions. Inhomogeneities in turbidity that occur at the heights of temperature inversions in the relatively clear atmosphere are also revealed by lidar. Examples of work in progress that show promise of providing a measurement of visibility are presented. It is concluded that lidar can already contribute usefully in routine meteorological service, but that its full potential in ceilometry and visibility measurement awaits further developments. For routine unattended use, high pulse-rate low peak-power lidars are advocated on grounds of safety.

Transport and oxidation of SO 2 in a stagnant foggy valley

The fate of SO 2 emitted in the San Joaquin Valley of California under stagnant foggy conditions was determined by the release of an inert tracer and the concurrent monitoring of SO 2 and SO 4 2− concentrations. At night, SO 2 was found to be trapped in a dense fog layer below a strong and persistent inversion based a few hundred meters above the valley floor. This lack of ventilation led to the accumulation of SO 2 and SO 4 2− over a major SO 2 source region in the valley. The rate of oxidation of SO 2 to SO 4 2− in fog was estimated at 3 ± 2% h −1. Production of acidity from the oxidation of SO 2 fully titrated the NH 3(g) present before the fog, and led to a progressive drop of the fogwater pH over the course of the night. In the afternoon, the valley was found to be efficiently ventilated by a buoyant upslope flow through the inversion. The tracer data indicated that about 40 % of the air transported upslope in the afternoon was returned to the valley in the night-time drainage flow. The fates of SO 2 and SO 4 2− in the valley during extended highinversion episodes appear to depend considerably on the presence of fog or stratus, and on the extent of daytime insolation.

Diurnal and Seasonal Patterns of Net Assimilation in Douglas‐Fir, Pseudotsuga Menziesii (Mirb). Franco, as Influenced by Environment

A 2—year study on net assimilation was carried out in a 38—year—old natural stand of Douglas—fir. Five trees in each of the dominant, co—dominant, and suppressed crown classes were studied using the cuvette method on intact branches and measuring the CO2 exchange with an infrared gas analyzer. Light intensity, air temperature, and relative humidity were monitored using selenium photocells, thermocouples, and a 2—mv, 24—line recorder. The net gain in photosynthesis in 1962 was found to be two to three times that in the drier year of 1961. Expressed per unit weight of dry foliage per hour, suppressed foliage possessed higher photosynthetic efficiency than co—dominants, which in turn were slightly more efficient than dominants. Douglas—fir could photosynthesize at low light intensities. The CO2 compensation point was commonly as low as 10 ft—c, and maximum rates of net assimilation were attained at 800 ft—c. Net assimilation could not be predicted from specific levels of air temperature, light intensity, or relative humidity, but not found to be directly related to light intensities below 750 ft—c and to air temperatures above 30°C. Apart from these extreme situations, net assimilation under natural conditions is apparently limited by the interaction of many internal and external factors. Diurnal patterns of net assimilation differed in trees of different crown class. The rates of photosynthesis and nocturnal respiration commonly fluctuated within each diurnal pattern despite apparently stable environmental conditions. The causes of midday depressions are complex as depressed patterns occurred under hot conditions in summer and under cool, foggy conditions in autumn. Bursts of CO2 evolution immediately after sundown, lasting up to 2 hours, were commonly observed in summer and autumn.