Air pollution in the city is an increasingly global issue, with people travelling or even relocating ever further afield.  If you are planning a trip, or a move, you'll want to take account of what levels of pollutants like particulate matter (PM) ozone are like in your destination city – especially if you suffer from asthma or another health problem that is exacerbated by exposure to pollution. 

For instance, California may sound like a dream destination but, in fact, an area in the Central Valley has just recorded the worst US air quality for several years.  Apparently, dry stagnant air in recent weeks has caused levels of ozone and PM to soar between the towns of Modesto and Bakersfield, breaking federal standards on most days. 

So it was no surprise to learn from the American Lung Association's 2011 State of Air report that Bakersfield is America's pollution hot spot,

There are so many different kinds of air purifiers and air cleaners on the market, that it’s hard to know where to start if you want to buy an air purifier for your home. Let’s start by listing the main types of air purifiers, and how they can help you. In other words, what’s in the box, and how does it work? I can’t tell you which air purifier to buy, because different models and brands have different strengths - but let’s imagine your primary concern is particle pollution in form of house dust mite allergens (whose allergen particles range from 0.1 to 10 microns in diameter).

HEPA Air Purifiers

The US Environmental Protection Agency recommends HEPA (high efficiency particulate air) filters, saying they are the most effective of the mechanical air cleaners. The HEPA is a specialized filter consisting of a folded mat of fibres. It has three different modes of action, each of

Throughout the crisis around Japan’s Fukushima nuclear power plant, we got asked a lot if air purifiers can help filter out radioactive air pollution. The high efficiency particulate air (HEPA) filter is well established in its ability to trap radioactive particles. The HEPA filter system was developed by the United States Army Chemical Corps and the United States Atomic Energy Commission during the Manhattan Project (development of the atom bomb) to protect against the spread of radioactive dust. The first HEPA filters were rigid and unwieldy machines, quite unlike their modern counterparts. They contained asbestos imported from Africa or Bolivia. Concern over the health impact of asbestos led to the development of alternative materials. There were also concerns about leaks and defects in the filter so, again, research was needed into a better filter material.

The HEPA filter was by no means the first air purifier. People have always been concerned about the quality of the

It makes sense to clean up the air in your home with a HEPA (high efficiency particle arresting) filter, and there are many scientific studies backing up their use. Some of the studies have been larger and for longer then others. With a quick search, I found ten trials on the impact of HEPA filters, but the largest one involved only 45 people. Two of the studies involved children, which is a helpful because, we get often asked about HEPA filters by parents who want to improve their children's asthma symptoms. We do know, from previous research, that HEPA filters can reduce levels of airborne particles and of nicotine. A new study shows how HEPA filters can help children with asthma who are exposed to secondhand smoke. Not only does secondhand smoke make asthma worse, it is of course also associated with many other health risks.

A group of 225 children took part in the 'Cincinnati Asthma Prevention Study'.

Research carried out by Dr. Bill Wolverton at NASA's Stennis Space Center has investigated how plants are able to remove pollutants from indoor air. The goal of Dr. Wolverton's decade long research was to find out how plants can help humans spend long periods of time in outer space. Dr. Wolverton was especially interested in preventing the inhabitants of the Skylab space station from getting sick due to off-gasing of chemicals from building materials. Formaldehyde, benzene, and trichloroethylene are just some of the potential carcinogens and irritants that building materials produce as by product. These irritants can quickly accumulate and create a toxic indoor environment, leading people to suffer from what is called "Sick Building Syndrome".

Dr. Wolverton's research showed that some plants emit water vapour that pull contaminated air towards their roots. Leaves, roots and bacteria in the potting compost

A HEPA air purifier is a powerful weapon in your fight against mold because it will effectively capture mould spores in the air. But it is also important to tackle the main cause of mold, which is damp conditions and, if mold has built up, to remove it - either with a bleach-based cleaner, a non toxic anit-allergen spray such as ADS from Allersearch, or if it is really bad, with professional help.

Mould is the name given to small, multi-celled fungi. Mushrooms are also fungi, as are yeasts, which are single-celled fungi. Moulds include the black mould Stachybotrys chartarum which is often mistaken for ordinary household dirt and the dark-coloured Alternaria mould which often lurks in bathrooms and can trigger severe asthma attacks. A recent paper in the journal Thorax reveals that the presence of mould and dampness in the home can lead to a deterioration in lung function.

What can you expect from an air purifier? That of cause depends which brand and model of air purifier you buy. We do not recommend buying an air purifier from a company that reverse engineered their product - even if that company has a household name and produces excellent other products, such as tvs, cars or even duct tape. By reverse engineering I mean to say that the company started out by asking the wrong questions, such as: How much should the air purifier cost? How much shelf space can it occupy at the local retail store? What new and exciting sounding technologies does it combine? Who is going to do the R&D for us and how much are we willing to pay for it?

The right questions to ask are: What is the average room size? How many air changes per hour does an air purifier need to achieve in such a room? What is the best possible filtration efficiency achievable? How can we guarantee the air purifier's reliable