Polluting the Internet

UK Air Pollution: March 2014

Will Morgan March 14, 2014

After the UK’s wettest winter since 1910, spring has sprung with several warm and clear days in March so far. High pressure has been the dominant meteorological situation, which has seen clear skies during the day and cold nights, with fog settling overnight and continuing into the morning. While the high pressure and much reduced rainfall has brought much needed respite to those affected by the severe flooding during the winter, it comes with a sting in the tail in terms of air quality.

Surface pressure analysis chart for midnight on the 14th March 2014. Source: Wetterzentrale.de and the Met Office.

This is illustrated on the graph below, which shows hourly aerosol mass concentrations from four sites in England from the beginning of February through until 0800 on the 14th March. Throughout February, the concentrations were relatively low at the four sites. Once we move into March, there are periods of increased aerosol concentrations lasting a few days at a time.

Aerosol mass concentration expressed as particulate matter with a diameter of less than 2.5µm from four air quality monitoring stations in England during February and March 2014. Data source: UK-Air.

The interesting thing about the past week has been that the concentrations have risen at all of the sites. While Manchester, London and Portsmouth are likely to have a large contribution from more local urban sources, such as cars, Harwell is in Oxfordshire and is less influenced by such sources. This suggests that the pollution event is also regionally driven. The meteorological situation recently has led to air from mainland Europe being blown across the UK and this air is likely contributing to the pollution situation.

This is typically a strong driver of regional pollution episodes in the UK, as easterly or southerly winds bring pollution from the continent to the UK, which exacerbates more local pollution problems. My PhD research focussed a lot on this very phenomenon; a couple of open access papers I wrote are available here and here. We found that such periods were often associated with enhanced concentrations of ammonium nitrate aerosol, which forms due to a combination of urban and agricultural emissions.

I suspect that this particular species of aerosol will be playing a role in the current pollution episode.

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Update: 17/03/14

A change in the weather over the weekend brought stronger winds over the UK, helping to disperse the build-up of pollution. This saw a large decrease in pollution levels over the UK, as seen in the updated graph below.

In terms of what next for the pollution, the answer is blowin’ in the wind.

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Air quality data acknowledgement

Fires in South East Asia

Will Morgan February 25, 2014

Smoke from a number of agricultural fires is currently blanketing Thailand and Cambodia. This is shown below in the satellite image from the MODIS instrument on the TERRA satellite. The red dots are classed as ‘thermal anomalies’ by the satellite instrument and are usually indicative of fires burning in these locations.

The majority of the fires are occurring in grass and cropland areas, which are the bale brown portions of the land surface in the image. This is indicative of agricultural burning, where farmers clear land and use the fires to recycle nutrients ahead of the growing season. In South-East Asia, the fire season usually runs from January to April/May.

Image of fires in South East Asia and the associated smoke haze from 24th February 2014 from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the TERRA satellite. Image courtesy of the NASA Earth Observatory. Click on the image for a larger view.

While the burning is beneficial to farmers, it isn’t too good for air quality in the region. The smoke generated by the fires has built up over Cambodia and Thailand (contrast the clearness of the image in the top-left over Myanmar with the haze to the east). The MODIS instrument on the satellite can also measure the amount of pollution in the atmosphere. This is known as the aerosol optical depth, which is well above 0.5 across the region. For context, a fairly polluted day in North-Western Europe might seen an aerosol optical depth of around 0.2.

This build up of pollution is harmful to health and can also cool or warm the atmosphere depending on the properties of the smoke. The side affects of such changes are uncertain but they could for instance alter atmospheric circulation patterns and rainfall.

Fires are a frequent occurrence across the globe and their impact can have long lasting consequences on our health and climate.

A continent on fire

Will Morgan December 4, 2013

While preparing my poster for the upcoming AGU Fall Meeting, I downloaded some data on fire activity in South America for background on why we are interested in biomass burning in the region. I wanted to quickly check I had the data in the correct format, so I just plotted the coordinates of the fire counts without an outline of South America.

I was surprised to see that the fire locations for August-October 2012 did a great job of outlining South America on their own!

Map of fire locations during August-October 2012 in South America from MODIS data from the Terra and Aqua satellites provided by NASA’s Earth Observing System Data and Information System (EOSDIS).

The data is from the MODIS instrument on NASA’s Terra and Aqua satellites. The data reports fire locations based on measuring the emission of infrared radiation by the land surface from space (like the infrared cameras on your favourite police chase tv show). Any 1km pixel with a fire detected within it is then included in the data – there could be more than one fire within the pixel but the instrument can’t distinguish these. You can find out more information about the technique here.

The widespread nature of the burning across South America is striking. Huge areas of the continent have fires detected within them. This is an annual endeavour with many of the fires started by people for land use change and agriculture. The main “season” runs from August to October, with the peak usually in September. These fires have been occurring for several decades now and they have transformed vast swathes of South America.

The burning produces large amounts of smoke, which can build up and pollute our atmosphere. This has important consequences for regional and global climate, air quality and also ecosystem development. I’m part of a project called SAMBBA, which as well as being a great acronym, is attempting to address some of the aspects of biomass burning that we don’t understand (which is a long list). I’ve written about the project and my part in it here and here previously.

As the map above illustrates, it is quite a big deal in the region. Stay tuned for future updates on the project.

Spoiling the view

Will Morgan November 21, 2013

Probably the most obvious manifestation of air pollution comes when looking out of the window and scanning the horizon – does the landscape go on for miles or is the view reduced? The build-up of air pollution can often dramatically reduce visibility via a shroud of haze.

On a recent trip to the Turkish Mediterranean coast near Antalya, the impact of air pollution on visibility was abundantly apparent. Below are two photographs I took of the view.

View of the Beydağları Mountains in Antalya Province, Turkey. The top image is from the morning of 11th November 2013, while the bottom image is at sunset on the 12th November 2013. Photographs by Will Morgan (me).

The photographs look out to the west from the hotel I was staying in. In the top picture, there is little to see aside from a few tall buildings just observable beyond the trees in the foreground. In the bottom image though, the Beydağları Mountains can be seen, although the view is still hazy. The mountains were approximately 20 miles (32 km) away, so to not be able to see the mountains at all in the top picture requires a large amount of haze. During the ten day trip, views like the top image were far more common.

Antalya province is surrounded by the Taurus Mountains, with the Mediterranean sea to the south, so it forms a bowl-like basin where air pollution can build. It is also very sunny, which gives atmospheric chemistry an extra kick to form air pollution. This cocktail is similar to other pollution hotspots such as Mexico City and Los Angeles.

The other key feature is that temperature inversions are common in Antalya. Typically, the temperature cools in the lowest part of the atmosphere with height but these inversions see a reversal of this trend within the first few hundred metres, which prevents air rising and mixing efficiently. You end up with a basin with a lid on it, so when pollutants are emitted into this, they find it difficult to disperse. This is like mixing a squash or cordial with water and only filling the glass half way with water – the amount of cordial (pollutant emissions) remains fixed but the reduced water level (temperature inversion) sees the concentration rise. Below is a video of a demonstration of temperature inversions, which actually refers to air pollution in Denver.

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The apparent major source of air pollution in Antalya is the burning of low-quality coal and domestic wood burning, which is particularly prevalent during the winter. I also noticed small fires from agricultural and trash burning during my stay. Summer temperatures typically exceed 30°C, so air conditioning is common rather than central heating systems. Evening and overnight temperatures during the winter drop below 10°C, so some form of heating is required.

The impact of air pollution on visibility is clear in the region and the health implications are also known, with Doctors warning about the risk from air pollution. Just this week, there were news reports warning that Antalya would experience poor air quality this winter.

Tackling the challenge is not easy though, especially given that the geographical and meteorological conditions in the region can’t be controlled. Antalya illustrates the interplay between these natural factors and our own role in pollutant emissions, which presents particular difficulties when trying to improve air quality. This interplay is prevalent across the globe.