Sentinel-5P data shows haze over UK pollution hotspots

8 August 2018

An early indication of the power of Europe’s new atmosphere monitoring satellite has come in the form of a nitrogen dioxide (NO2) map of the United Kingdom, built from Sentinel-5P data by Leicester-based air quality monitoring specialist EarthSense.

No surprise, the map – a series of daily views for the week of 25 June and claimed to be the first of its kind – shows high NO2 concentrations in the major urban conurbations of London, Birmingham and Liverpool/Manchester. But with Sentinel-5P providing 7km resolution, the result is about 10 times more information than has been available from previous satellites. The result, says Professor Roland Leigh, EarthSense technical director and an air quality researcher at the University of Leicester, is better understanding of key pollution sources and population exposures.

Leigh says EarthSense intends to follow up this initial exercise with two NO2 monthly maps using Sentinel-5P data. He’ll be looking to compare how well the satellite data reflect known sources of pollution across the UK, such as large industrial ports. The UK has some very good air quality modelling techniques and success here would give confidence to satellite-based products developed for use in parts of the world where pollution sources are not so well known or monitored, he says.

The Sentinel-5P-based NO2 mapping exercise follows MappAir, a product developed by the company last year combining data from satellites and its own air quality monitoring sensors with open source data, including traffic emissions, weather conditions and other information, to produce annual averages across the UK – initially at 100 metre resolution. And, just as better satellite data will enable more accurate pollution snap-shots and forecasts, increased ground sensor use can feed into ever higher resolution maps. EarthSense envisions a range of maps including an ultra-high resolution 1 metre dataset for detailed study areas, a 10 metre map for urban areas, an historic time series of maps showing how air pollution changes over the course of a day and on different days, and forecast maps giving an indication of fluctuations up to three days ahead.

Meanwhile, EarthSense is taking its own direct approach to pollution measurement by bringing its Zephyr air quality sensor into “mass production” to reduce unit costs and has targeted over 100 units in its first production run. Little bigger than a loaf of bread and designed to be installed in fixed locations or carried on moving platforms, Zephyr features a replaceable cartridge system to sample local air and measure pollutants including NO2 and ozone as well as background humidity and temperature. Zephyr can also measure particulate matter, sulphur dioxide (SO2), carbon monoxide (CO) and hydrogen sulphide (H2S).

EarthSense is also developing an app to guide users to the least polluted routes when walking, running or cycling. Funded by a European Space Agency kickstarter grant, CARAMEL – Clean Air Routing and Mobile Exposure Limitation – uses data from multiple sources to identify the cleanest air routes, report on weekly pollution levels and help planners develop clean air strategies.

The company, just 18 months old, aims “to be a global leader in accurate air quality monitoring, modelling and data for decision-making”.

Neighbourhood nose: EarthSense’s Zephyr air quality sensor is now in commercial production (EarthSense)

Launched in October 2017, Sentinel-5P is the newest satellite in Europe’s Copernicus Earth observation programme. Its key instrument is a Dutch-supplied spectrometer called Tropomi, designed to map pollutants such as NO2, methane, carbon monoxide and aerosols that affect health and climate. Speaking when the first imagery was returned following launch, European Space Agency director for Earth observation Joseph Aschbacher underscored the importance of monitoring air quality by noting that some 6.5m people worldwide, and 500,000 in Europe, are believed to die prematurely every year owing to air pollution.