Natural Air Polluters: The Unseen Danger

Natural sources of air pollution include wind-blown dust, dust storms, wildfires, and volcanic eruptions. These natural sources emit pollution into the air, which can be transported over short or long distances by the wind. While natural sources of air pollution can be significant, they typically do not create persistent air pollution issues compared to other sources, such as industrial activities or vehicle emissions. Nevertheless, natural sources contribute to particulate matter (PM) pollution, which includes airborne substances that are not gases, such as microscopic solid particles or droplets suspended in a gas.

Wildfires

PM from wildfire smoke can be divided into two main categories: coarse particles (PM10-2.5) and fine particles (PM2.5). Coarse particles are those with diameters larger than 2.5 micrometres (µm) but smaller than or equal to 10 µm. While coarse particles are primarily generated by mechanical operations like construction and agriculture, they are also present in wildfire smoke. On the other hand, fine particles are those with diameters of 2.5 µm or smaller, and they make up about 90% of the total particle mass in wildfire smoke. These fine particles are of greater concern to public health as they can travel deep into the lungs, and the smallest, ultrafine particles, with diameters less than 0.1 µm, can even enter the bloodstream.

The health effects of wildfire smoke are well documented. Individuals at greater risk of adverse health outcomes from exposure to wildfire smoke include those with pre-existing cardiovascular or respiratory disease, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status. The particles in wildfire smoke can aggravate existing health problems and increase the risk of heart attack or stroke. Additionally, the smoke can cause haze, reducing visibility and impacting air quality.

To protect public health during wildfire events, it is crucial to monitor air quality and take appropriate measures to reduce exposure to smoke. When air quality deteriorates due to wildfire smoke, staying indoors with windows and doors closed is the most effective way to minimize smoke inhalation. In areas with central-ducted air conditioning and heating systems, setting the system to "on" ensures constant air filtration. Installing high-efficiency filters and using air cleaners can also help reduce indoor particle levels. During evacuation, it is important to keep vehicle windows closed and run the air conditioner in recirculation mode to prevent smoke inhalation while travelling to areas with better air quality.

Volcanic eruptions

Volcanic ash clouds can disperse widely, spreading harmful particles through the Earth's atmosphere. The size of the ash particles plays a crucial role in determining the extent of the ash cloud; smaller particles allow the cloud to extend further and disperse more broadly. Wind speed and direction also influence the movement and reach of the ash cloud.

Volcanoes emit various gases, including carbon dioxide, sulphur dioxide, and sulphuric acid. Carbon dioxide, due to its lightweight nature, is easily expelled and dispersed during volcanic eruptions. It accumulates in high concentrations near the Earth's surface, trapped under a layer of heavier air. This gas is harmful to humans and animals, causing unconsciousness and even death at high levels of exposure. Sulphur dioxide, another common volcanic emission, can lead to the formation of sulphuric acid rain, which negatively affects terrestrial ecosystems and human populations. The United States Geological Survey has warned of the health risks associated with sulphuric acid exposure, with potential irritation occurring in the nose, throat, eyes, and skin at certain concentrations.

The impact of volcanic eruptions on air quality can be significant, as evidenced by the 1980 eruption of Mount St. Helens, which resulted in an international pollution event. The eruption released a massive amount of sulphur dioxide into the atmosphere, and the resulting ash cloud migrated across the United States in just three days, eventually reaching worldwide in 15 days. Another notable example is the 1986 eruption of Mt. Kilauea in Hawaii, which also had widespread international effects. The United States Geological Survey highlighted the persistent health problems caused by acid rain and air pollution downwind from the volcano during its active phase.

Dust storms

The sky may turn brown, yellow, orange, red, or grey during a dust storm, and visibility may be impacted. Dust storms can vary in duration, lasting from a few hours to several days, depending on factors such as wind speed, the amount of dust available, and local terrain conditions. Climate change contributes to the increasing frequency, duration, and intensity of dust storms by exacerbating desertification.

To protect yourself during a dust storm, it is recommended to stay indoors and, if necessary to go outside, to wear a KN95/FFP2 mask. Running a high-performance air purifier can help filter particles, gases, and other pollutants from the air.

Wind-blown dust

The health effects of wind-blown dust are well-documented in hundreds of studies. The particulate matter carried by wind-blown dust can be associated with respiratory diseases such as asthma and bronchitis, as well as cardiovascular disease. Additionally, wind-blown dust can transport pathogens and toxic substances, posing various hazards. For example, the Western Hemisphere faces the unique challenge of coccidioidomycosis, or Valley fever, which is caused by exposure to a soil-dwelling fungus endemic to the Americas. While most cases are mild, some can be disabling or even fatal for both humans and animals.

To address the issue of wind-blown dust and its impact on air quality and public health, various dust control methods are employed in different regions. In California, for instance, dust control strategies are tailored to the local soil properties, topography, and meteorology. Similarly, in Benton County, the Columbia Plateau Project has been working to minimize wind-blown dust and address PM-10 National Ambient Air Quality (NAAQS) violations caused by natural events, with a focus on protecting public health and informing the public about unhealthy air quality.

Sea spray

The composition of sea spray depends on the composition of the water from which it is produced. It primarily consists of a mixture of salts and organic matter, including dissolved organic carbon (DOC) and even microbes such as bacteria and viruses. During the winter months, stormy and windy conditions contribute to increased air inundation into the sea, leading to higher sea spray production. In contrast, calmer summer months result in lower sea spray formation. However, during peak primary productivity in the summer, increased organic matter in the surface ocean drives subsequent increases in sea spray.

The formation of sea spray droplets is influenced by local conditions and spatial patterns. These droplets exhibit the same properties as the ocean surface but rapidly adapt to the surrounding air. Some sea spray droplets reabsorb into the sea, while others evaporate and contribute salt particles like dimethyl sulfide (DMS) to the atmosphere. DMS plays a role in cloud formation and interacts with solar radiation, impacting climate patterns. Additionally, sea spray can contribute to the global sulfur cycle.

While sea spray can contribute to air pollution, it also has a cleansing effect on the atmosphere. The large sea salt nuclei in polluted clouds over the oceans can initiate rainfall by collecting small cloud droplets formed on pollution particles, thereby purifying the air. Furthermore, coarse sea spray has been found to inhibit lightning development in storm clouds.

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