Exploring the effect of weather on air quality in Chorlton

As part out Our Streets Chorlton, ODM has been running monthly ‘Data Chats’, where we explore some of the data collected by the community.

In February we were joined by Blaise Kelly, an air quality expert and ex-Chorlton resident, who gave a talk on how the weather affects air pollution before giving some examples using data collected by our air quality monitors.

This is a short blog with some key takeaways from Blaise’s talk – watch the full video online here or at the bottom of this blog.

 

A bit about weather data

 

• There is a large amount of weather data freely available from sources such as the National Oceanic and Atmospheric Administration or the Environment Agency or the European Centre for Medium-Range Weather Forecasts – but you’ll need to know a bit of R to access it.
• You’ll also need to do a bit of data munging to consolidate the data with the AQ data. For example, weather data was taken from Manchester Airport, which has data with time stamps of 20 past and 10 to every hour (ie XX:20 and XX:50 where XX is the hour), whereas our AQ data is in minutes. Blaise had to do a bit of stitching and matching using R with the Dplyr package.
• Blaise has written some code and you can find it here.

 

Darley Avenue and NO2

 

Source: Blaise Kelly

When looking at Darley Avenue, there were high concentrations of PM2.5 registered when the wind blows from the road and houses. The highest concentrations were at 8-9pm, so the initial thinking was that it would household heating – such as wood burners. However, these highest concentrations occurred when the temperature was in the 11-15 degrees range – suggesting that these high concentrations were actually coming from the road in the evening, and not the houses.

NO2 is less influenced by wind and it breaks down quite quickly. For every metre or two away from the road NO2 drops off quite significantly. Whereas gas boilers are the second highest cause of NO2 pollution, they tend to be next to people’s houses and not on the roadside. As our AQ monitort on Darley Avenue was located on the roadside and away from any building, it is highly likely that any NO2 reading picked up is for cars.

This is backed up by the fact that there were high concentrations of NO2 the same time as high PM readings. Notable pleaks for both between 7-8am.

 

Source: Blaise Kelly

 

Data from our Four Banks location showing the boundary layer effect

 

The ‘atmospheric boundary layer’ is part of the Earth’s atmosphere that directly affects and is affect by the eath’s surface. It can range from a few metres high to a few kilomteres high, depending on the weather.

When the boundary layer is high, weather tends to be clear and sunny. Therefore there will be more ozone recorded, as sunshine contributes to the breaking down of NO2. When the boundary layer is low, there tends to be less sunshine, and therefore less ozone recorded. However, NO2 will be higher. Examples of this effect were demonstrated using the data from the air quality monitor data from Four Banks.

 

And mystery pollution at Sandy Lane in December

 

From August onwards, we relocated our Darley Avenue monitor to Sandy Lane. NO2 levels remained relatively low until December, when high concentrations were recorded, with the highest between 10am and 3pm. With such a spike in December, Blaise queried whether there was any construction machinery nearby, either on Sandy Lane itself or on Nell Lane – the weather was blowing from the south east, so could have been blowing in from this direction.

 

Source: Blaise Kelly

 

One suggestion was that this could have been from nearby construction machinery, as non-mobile road machinery doesn’t actually have to pass any emissions standards, and so could have been contributing to this sudden spike in readings, but a few residents local to the area couldn’t recall their being roadworks at this time.

 

If you have an idea of what may have cause this spike in NO2 in December, let us know either by email or on Twitter.

For a more in depth exploration into how weather affect air quality, and a deeper exploration of the Chorlton data, watch the full video below.

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