Outdoor Air Pollution and Pollutants:
The major outdoor air pollution that allergy sufferers have to contend with are derived from burning fossil fuels – in particular sulphur dioxide, particulate matter (pm), nitrogen dioxide (NO), carbon monoxide (CO), acid aerosols, and ozone (O). Ozone is a secondary air pollutant, and it is created when sunlight reacts with vehicle exhaust products (NO) in the presence of hydrocarbons. Ozone is, therefore, termed a photochemical pollutant.
The levels of outdoor air pollution you are exposed to will depend on a number of factors, including local production, sunlight, and the prevailing winds. A high-pressure weather system, which is characterized by fine, hot weather with clear skies and little or no wind, will increase the likelihood of pollution-laden fog, or “smog”.
Outdoor pollutants and allergies
The ever-increasing number of people suffering with allergies inevitably introduces the suspicion that pollution is responsible for these diseases. While the incidence of allergy has increased, air pollution particularly that from sulphur-containing fossil fuels, has in fact decreased.
A study made after the reunification of Germany, reported that there were higher levels of SO, NO2, and particulate matter in Leipzig (old East Germany) compared with Munich (old West Germany). However, the much higher incidences of atopy and allergic disease in Munich suggest that exposure to these outdoor air pollution does not increase the risk of allergy. Respiratory infections are, however, certainly increased by exposure to high levels of these air pollutants, as are incidences of bronchitis.
At road level, the exposure to the pollutant NO; (nitrogen dioxide) directly relates to the density of vehicular traffic. Exposure to SO, NO, and ozone have all been shown to worsen asthma and rhinitis as well as contributing to conjunctive disease.
The worsening of asthma due to outdoor pollutants may occur for a number of reasons. For example, many of these pollutants are irritants, and so exposure to SO, and NO, may induce an acute narrowing of the airway. Associated with this is breathing difficulty, while exposure to ozone causes coughing and an inability to breathe deeply, which again leads to the sensation of breathlessness.
When you breathe through your nose, a process of absorption removes SO., and this helps to protect the lower airways. However in individuals with allergic rhinitis, a symptom of which is a blocked nose, this crucial protection is lost, and when you breathe through your mouth, the SO, goes straight to the lower airways where it worsens the asthmatic condition. Similarly, when taking physical exercise you tend to breathe more through the mouth than nose. This means that jogging or cycling in polluted air for example, will have a greater effect in worsening asthma than either the exercise or the pollution by itself.
Common external pollutants may also worsen any airway inflammation you already have, leading directly to a prolonged worsening of the asthma and a tendency to experience more severe attacks. This effect is most noticeable with ozone, where there is a 24-hour time delay between peak exposure and the worsening of your underlying condition.