This then is the conundrum; we need air to circulate from outside to inside, but in areas with substantial external pollution that circulation continuously brings harmful outside pollution into our homes.

​Outside, Nature wages a powerful war of attrition against atmospheric pollution. ​

Wind disperses pollution, diluting its local effects. Natural chemical and photochemical interactions create an abundance of ‘hydroxyl radicals’ (called ‘Nature’s Detergent’ by scientists) which attack and neutralise a wide range of pollutants, and rain and snow wash pollution and its by-products out of the air. ​

Of course, in the urban environment, pollution can build up where it is created more quickly than nature can remove it.

Inside, the natural conditions which create hydroxyls are absent, and pollution, well, it hangs around for us to breathe it in!

​These days, the major threat to clean air is now posed by traffic emissions. Petrol and diesel powered vehicles emit a wide variety of harmful pollutants, principally carbon monoxide (CO), oxides of nitrogen (NOx), volatile organic compounds (VOCs) and particulate matter (PM2.5). Additionally, the photochemical reactions resulting from the action of sunlight on nitrogen dioxide (NO2) and VOCs create ozone. 

​CO (carbon monoxide) is a dangerous, colourless gas which reduces your blood’s ability to carry oxygen and can make you ill. 

The Committee on the Medical Effects of Air Pollution recently reviewed the evidence for the adverse health effects of NOx and concluded that:

• Short-term exposure to NO2 likely causes respiratory ill health, may cause an increase in hospital admissions for heart problems, and may cause an increase in overall mortality.
• Long-term exposure to NO2 may cause an increase in respiratory and cardiovascular mortality, children's respiratory symptoms, and decreased lung function.

​VOCs include a variety of chemicals, some of which can have short- and long-term adverse health effects.

​Ozone can trigger asthma attacks and cause shortness of breath, coughing, wheezing, headaches, nausea, and throat and lung irritation, even in healthy adults.

​Particulate matter, also called PM or soot, consists of microscopically small solid particles or liquid droplets suspended in the air.

Ultrafine particles (UFPs) are particulate matter of nanoscale size (less than 0.1 microns in diameter). UFPs are the main constituent of airborne particulate matter. Owing to their numerous quantity and ability to penetrate deep within the lung, UFPs are a major concern for respiratory exposure and health​

PM pollution can cause lung irritation, aggravates the severity of chronic lung diseases, causes inflammation of lung tissue, causes changes in blood chemistry and can increase susceptibility to viral and bacterial pathogens.

​Think about it this way: Sit an air cleaner, however effective, next to an open window, and it will be overwhelmed by new pollution to the point where it will have no effect. For an air cleaner to be effective, you have firstly to slow the flow of new air into a room to give it time to work.

So, reducing leakage is only the first step in mitigating the pollution problem. The second step is using an air cleaner that really works!

​Having reduced air leakage, let’s look at our options for removing or neutralising polluting gasses and particulates before we breathe them in:

These are sometimes suggested to remove these gasses from the air and can be implemented either as stand-alone filters or in combination with a HEPA filter to capture the larger particulates.

The ‘gold standard’ for particulate filters is the High Efficiency Particulate Air (HEPA) filter. Filters meeting the HEPA standard remove 99.97% of particles that have a size 0.3 microns or larger from the air passing through them.

However, 90% of particulates in the air, including the most harmful ones, are smaller than that, so most HEPA air purifiers only catch a fraction of all particulates, and none of the potentially most harmful ones. 
X Hepa Filters will only remove 10% of the particulates.

​​Correct. And air filters don't work well in the real world anyway! Not only are there no suitable and affordable filters for the purposes we require, the unfortunate fact is that portable air filtration devices, of whatever type, are not very effective at treating any kind of pollution. ​

All portable air filters share the same fundamental shortcoming; even if they do filter the air passing through them effectively, they only clean that limited amount of air that passes directly through them, not all of the air in the room. You can find out more here.

​Outside, Nature wages a powerful and successful war of attrition against atmospheric pollution by employing natural chemical and photochemical interactions to create an abundance of ‘hydroxyl radicals’ (known as ‘Nature’s Detergent’ by scientists) which attack and neutralise a wide range of pollutants.

Find out more about how Airora breaks down harmful gasses and vaporises key ultra-fine particulates that are too small to be trapped by HEPA filters here.

​​​Hay fever is a type of allergic rhinitis caused by pollen or spores. Allergic rhinitis is a condition where an allergen (something that causes an allergic reaction) makes the inside of your nose inflamed (swollen).

People with hay fever can experience their symptoms at different times of the year, depending on which pollens or spores they are allergic to.

​Hay fever symptoms vary in severity and your symptoms may be worse some years than others, depending on the weather conditions and the pollen count (see below). Your symptoms may start at different times of the year depending on which types of pollen you are allergic to.
The symptoms of hay fever include:

• frequent sneezing
• runny or blocked nose
• itchy, red or watery eyes (also known as allergic conjunctivitis)
• an itchy throat, mouth, nose and ears

​Less commonly, you may experience:

• the loss of your sense of smell
• facial pain (caused by blocked sinuses)
• sweats
• headaches

​​Hay fever symptoms are caused by protein molecules in pollen grains. The immune system ‘over-reacts’ to these allergens, which it manifests in the form of an allergic reaction. Immune molecules known as Immunoglobulin E are produced and these cause the release of the inflammatory chemical called histamine from mast cells (a type of immune cell).

​It is histamine that produces the characteristic symptoms of an allergic reaction.

A non-allergic person’s immune system will not produce this reaction on exposure to allergens in pollen.

​Research shows that students’ academic performance may be affected during exams, given that the exam season usually coincides with the height of the pollen season. 

​Hay fever is a relatively new disease, first described in 1819. It took nine years to accumulate enough hay fever cases to present a paper on this new condition to a medical journal. Now hay fever is much more common, particularly in the UK, which has more cases than anywhere else in the world (followed closely by Ireland, New Zealand, Australia and Canada). Hay fever:

• ​is the most common allergic disease
• affects 10-25% of adults in the UK
• affects 10% of children (aged six-seven) and 15% of those (aged 13-14)
• is now being seen in children as young as three and four years old

​If you have asthma, your asthma symptoms may get worse when you have hay fever. Sometimes, asthma symptoms only occur when you have hay fever. These symptoms include:

• tight chest
• shortness of breath
• coughing
• wheezing

Hay fever symptoms are likely to be worse if the pollen count is high. The pollen count is the number of grains of pollen in one cubic metre of air.​

​​Air samples are collected in traps set on buildings two or three storeys high. Taking samples from this height gives a better indication of the pollen in the air from both local and distant sources. Traps on the ground would only collect pollen from nearby trees and plants.

The air is sucked into the trap and the grains of pollen are collected on either sticky tape or microscope slides (glass plates). The pollen is then counted. Samples are usually taken every two hours, and the results are averaged for a 24-hour period. ​

​Hay fever symptoms usually begin when the pollen count is over 50. The pollen count is usually given as part of the weather forecast during the spring and summer months.

​Spores that cause hay fever can come from:

• fungi, such as wild mushrooms, and
• mould, for example from compost heaps​

​​Different trees and plants produce their pollen at different times of the year.

During their pollen season, plants release pollen early in the morning. As the day gets warmer and more flowers open, pollen levels rise. On sunny days, the pollen count is highest in the early evening.

​It is very difficult to completely avoid pollen or spores. However, reducing your exposure to the substances that trigger your hay fever should ease the severity of your symptoms. Follow the advice below to avoid being exposed to excessive amounts of pollen and spores. 

When indoors:​

​Finally, check the pollen count regularly to know when your efforts need to be more concentrated. 

​While numerous manufacturers of ‘air cleaners’ / ‘air filters’ claim to be able to clear pollen from the air, they can only reduce, not eliminate, the problem, because:

• they can only clean the air that passes through them, and stratification, eddies and more means that some air in the room never passes through the filter
• they don’t clean surfaces at all and it only takes a small disturbance to put settled pollen back into the air