Weather forecast – changeable!

Weather forecast – changeable!

We all know that when you are downwind of an odour you will smell it, whereas upwind you may smell nothing, but how does weather affect your environment and the impact on pollutants?


We have all experienced the impact that hot weather can have on odours and dust, but there are other types of weather that can also have a surprising effect on air quality.  Odour control solutions and dust suppression strategies need to consider these impacts to prevent unwanted problems.

For example, in winter a combination of low air temperatures, slow wind speeds and intense cloud cover can cause odours to build up in the atmosphere.

The impact of weather on the level of pollutants around the source of emissions is indisputable.  Differing weather conditions can affect the magnitude of air pollution by up to 70%.  Additionally, weather can significantly affect the dispersion and suppression of air pollution.

Wind will carry the air pollution away from the source, while its direction is mainly determined by the local topography. Wind direction changes with height, along with wind speed varying hourly. The greater the wind speed the more efficient the mixing with fresh air.  Low wind speeds in combination with high-pressure result in accumulation of dust in the atmosphere. The increase in the wind speed reduces the possibility of detachment of contaminants from the earth’s surface, which leads to the increase of the range and surface area of the spread of pollutants. Literature provides evidence for the intercontinental atmospheric transport of bioaerosols and dust, while odour was found to disperse at local scale (100 m – 10 km). When new installations are undergoing environmental permitting they must consider prevalent wind direction and location of the nearest downwind sensitive receptors in order to reduce potential exposure to pollution and odour nuisance.

Changes in air temperature can lead to formation of atmospheric turbulence which further enhances dispersion of air pollutants. However, elevated air temperatures combined with increased insulation may in fact trigger and accelerate photochemical reactions among airborne particles, resulting in (among others) ozone and smog production.

A low-pressure in conjunction with increased relative humidity enable aggregation of dust particles which speeds up the deposition process. The same weather conditions stimulate condensation of aromatic hydrocarbons in the atmosphere. Precipitation and snowing usually is considered as a favourable factor which purifies the air from pollutants; such as particulate matter and dust particles by washing them out. The wet deposition is particularly relevant for bioaerosols (e.g. grass, ragweed pollen), which often can be found as a serious cause of allergic reactions and asthma outbreaks. In contrast, increase in humidity can also facilitate release of fungal spores, particularly from the group of Ascomycetes, where changes in relative humidity influence spore release mechanism (“squirt gun”). In relation to other air pollutants, i.e., SOx and NOx in reaction with water, result in acid formation, commonly known as “acid rains” that cause irreversible damage to the environment.

In terms of air pollution, the worst weather scenarios occur during the winter season, at low air temperatures, slow wind speeds and intense cloud cover as air pollutants accumulate near the emission sources and remain stagnant for a substantial amount of time. Long periods without any precipitations can aggravate the local air quality further due to slow pollutant deposition process which then entirely depends on the gravitation force.

For advice on any odour or dust related problems, call Spectrum Environmental Support on 01905 362100 or email

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