Fog is a visible aerosol of tiny water droplets or ice crystals suspended in the air near the Earth’s surface. It forms when water vapor condenses, often resembling a low-lying cloud. While fog itself is not inherently harmful, it can create environmental conditions that indirectly lead to health concerns, primarily by trapping airborne substances.
How Fog Influences Air Quality
Fog significantly affects air quality by trapping atmospheric pollutants. As a dense, moist layer, it prevents the vertical dispersion of harmful substances. This concentrates particulate matter (PM2.5 and PM10) and gases like sulfur dioxide and nitrogen oxides, typically emitted from vehicle exhausts, industrial activities, and residential heating.
This trapping effect can lead to “smog,” a term derived from “smoke” and “fog.” The Great Smog of London in December 1952, caused by cold, windless conditions and coal-burning emissions, resulted in a thick, toxic layer. This event led to an estimated 10,000 to 12,000 deaths and made many more ill.
Moisture within fog can also facilitate chemical reactions, transforming less harmful pollutants into more toxic compounds, further exacerbating air quality issues.
Direct Health Effects from Polluted Fog
Inhaling air contaminated by fog-enhanced pollution can lead to health problems, particularly affecting the respiratory and cardiovascular systems. Fine particulate matter (PM2.5) can penetrate deep into the lungs, causing inflammation and reducing lung function. This can worsen existing respiratory conditions like asthma, chronic obstructive pulmonary disease (COPD), and bronchitis, and increase susceptibility to infections.
These airborne pollutants also impact cardiovascular health. PM2.5 can enter the bloodstream through the lungs, contributing to systemic inflammation. Short-term exposure has been linked to an increased risk of heart attacks, strokes, and irregular heart rhythms (arrhythmias). Individuals with pre-existing heart or lung conditions, the elderly, and young children are particularly susceptible to these adverse effects.
Beyond Air Quality: Additional Health Factors
Aside from air quality, fog can impact health in other, less direct ways. Reduced visibility, a characteristic of dense fog, significantly increases accident risk, including vehicle collisions and pedestrian falls.
Damp and cold conditions associated with fog can affect physical comfort and exacerbate certain ailments. While fog itself does not cause viral illnesses like colds or flu, prolonged exposure to a cold, damp environment can make individuals feel unwell. Some people with arthritis report increased joint stiffness and pain during cold and humid weather, though research on this connection is varied. The gloomy weather accompanying fog can also influence mental well-being, potentially contributing to lower mood, lethargy, or exacerbating seasonal affective disorder due to reduced sunlight exposure.
Staying Safe and Healthy in Fog
Taking proactive steps can protect health during foggy conditions. Monitor local air quality reports, especially if you have respiratory sensitivities. Limit outdoor activities, particularly strenuous exercise, when dense fog and high pollution levels are present.
Indoors, keep windows closed to prevent polluted air from entering homes; air purifiers may help improve indoor air quality. When driving in fog, reduce speed, use low-beam headlights and fog lights, and maintain ample distance from other vehicles due to reduced visibility. If experiencing respiratory symptoms during foggy periods, consult a healthcare professional.