Introduction

July and August has been an interesting month for Chippenham Air Quality. With London Road closed and one of our monitors at the centre of traffic diversion controversy it’s been an interesting time. The Wood Lane monitor readings were used as evidence to help add extra signage to prevent cars diverting through Wood Lane.

Wood Lane Air Quality July – August 2024

Wood Lane is an interesting case study here as road works on London Road by Wessex Water have resulted in a large quantity of vehicles diverting through Wood Lane during the closure. This seems to correspond with an increase in PM2.5 particulate pollution during the initial phase of the road works, decreasing on 4th August when new signage had been put in place and the problems received wide publicity on social media after which the Police also issued warnings about the No Right Turn at Wood Lane.

The Air Quality monitor is at the entrance of Wood Lane and the Avenue La Flèche junction.

Can we say this is cause and effect?

It’s difficult to say conclusively. Marshfield Road also received a slight increase above its higher background average at this point, though that could be a referred side effect. The Rowden Hill monitor was being repaired at this point. The Langley Road monitor showed no increases. So it is plausible that the increase in diverted traffic caused a decrease in air quality. The humidity and pressure records over the period don’t show changes over the same time scales.

Poor Air Quality 18th to 19th August

Interestingly Wood Lane, Rowden Hill, and Marshfield Road all show poor air quality between the 18th and 19th August. This is not reflected on Langley Road.

The monthly average for Wood Lane is 8.3 ug/m3 which is better than the previous measurement period, despite the peaks around the start of the road works.

Marshfield Road Air Quality July – August 2024

Marshfield Road showed the worst Air Quality this month and this is highly likely to be due to the continuous traffic seen at this location.

An increase is seen around the 30th to 31st July, which could be down to changing traffic patterns due to road works. The 18th and 19th August show the peak of pollutants also seen at Rowden Hill and Wood Lane.

Rowden Hill Air Quality August 2024

The Rowden Hill Air Quality monitor was down for repair for a couple of weeks (read later) so only a couple of weeks of August have been captured.

The peak around the 18th and 19th of August is seen as per Wood Lane and Marshfield Road.

Overall the average is significantly lower than the last measurement period, possibly due to school holidays reducing overall traffic.

Average 10.79ug/m3

Langley Road Air Quality July – August 2024

The Langley Road monitor has the lowest average readings, however there are unexplained peaks. The monitor is surrounded by more close proximity plants than the other monitors, so it could be related to pollen perhaps?

There is a known compromise in the software of these monitors that the inlet fan only runs for 5 seconds to preserve battery life. This could perhaps lead to erroneous spikes. It may be that an experiment with a longer fan duration could be tried.

Overall Air Quality

Marshfield Road 18.8ug/m3

Langley Road 11.72 ug/m3

Rowden Hill Average 10.79ug/m3

Wood Lane PM2.5 8.3ug/m3

This month all PM2.5 average readings were below 20ug/m3

Perhaps surprisingly Wood Lane had the lowest average, though this doesn’t reflect the peak seen for a week.

Changes made this month

All of the monitors are battery powered, and as luck would have it, all the batteries went flat after the first month. So a number of changes were made to extend the battery life…

• Higher power rechargeable batteries purchased
• Sample time changed from once every 15 minutes to once per hour
• Upload changed to once every 10 readings ie every 10 hours

The software used is open source and a newer software release was available to fix the bug that results in the disk filling up when wifi is lost. An attempt was made to update the Rowden Hill monitor to this new release, but unfortunately that resulted in an inability to connect to the monitor!. After long discussions with support the unit was sent back to Pimoroni and a replacement received.

The Dashboard links to the ‘live displays’ from our website would sometimes fail resulting in a blank screen. After discussions on the Adafruit.io forum their support gurus kindly bug fixed this and the dashboard links should now work.

There seems to be a slight peculiarity with the Wood Lane dashboard on some mobile screens that it will only show in landscape mode. ie rotate the phone. Despite my best efforts I have not yet fixed it.

The Langley Road monitor in particular is showing glitchy peak measurements that may be due to the close proximity to garden plants and pollen (we have a very wild front garden, as does Wood Lane, though the Wood Lane monitor is higher and not quite as close to the plants). The Langley Road monitor is also close to Wavin and the Cocklebury Lane gas fired power plant, though this is an observation only.

One fix could be to site the monitor a bit higher. The data sheet for the particulate sensor indicates the inlet fan should ideally be run for 20 seconds before taking a reading. Pimoroni have compromised on 5 seconds to extend battery life, but this could be leading to the spikes in the readings. So this may be a future tweak when the batteries next go flat.