Today, the eight million residents of London were warned of a 'public health emergency' as, for the second time in less than six months, a toxic air alert was issued for the city.

London breached its legal limit of toxic air for 2017 in the first week of January, after levels of nitrogen dioxide were continually recorded above the WHO limit (200 μg/m3) and this morning the Mayor of London's office issued a toxic air warning that is expected to last at least three days.

Around 9,000 deaths a year in London are related to poor air quality as well as an increasing number of people diagnosed with asthma and reduced lung capacity in children.

The increasing urban air pollution is a result of a factors, with population density in many cities growing at an astounding rate, more vehicles in cities and a reduction in green spaces mean that residents are exposed to more common pollutants than ever before.

This alert means that London joins a growing trend of European cities where air pollution has been determined toxic, Paris, Madrid, Sofia, Warsaw and Rome have all issued pollution warnings in the last 6 months, many banning traffic in the city centre to reduce harmful gases in the air.

"London's dirty air is a public health emergency," London mayor Sadiq Khan commented this morning. "We will continue to use all the technology at our disposal to inform Londoners about levels of air pollution in their neighbourhoods."

The environmental monitoring technology ecosystem has expanded rapidly over the last 2 years, new sensor technologies mean that over the coming years, coverage of air quality will improve dramatically, with cities being able to measure pollutant levels through hyperlocal monitoring nodes working in conjunction with handheld, mobile sensors attached to cars and bicycles to measure air pollution on much larger scale.

The market for environmental sensors, which we predict will be worth more than $3 billion by 2027 has already begun to show new products with many coming to market in 2017, a huge range of air quality monitors and purifiers utilising this new technology on display recently at CES in early January. Many of these products will be used by citizens to make decisions on when is best to exercise, travel and relax outdoors.

The new IDTechEx report Environmental Gas Sensors: Technologies, Manufacturers, Forecasts covers the broad range of technologies that make up the gas sensor ecosystem. The report takes a historical look at gas sensing and assesses the new wave of miniaturization, predicting the impact it will have on consumer electronics and the future of smart cities. All the key players are profiled and the market is analysed by application and by sensing technology.

Advancements in the way we monitor gases in urban areas combined with progress in air purification technologies will help to prevent dangerous levels of toxic pollutants in the future.

Top image: London, photo by D. Pugh, IDTechEx