Data Bulletin May 2021 – Traffic and Air Quality report for Barlow Hall Primary School, Darley Avenue

Traffic and Air Quality report for Barlow Hall Primary School, Darley Avenue

May 2021


Cars on Darley Avenue Headline information

With Barlow Moor Road being reopened after its resurfacing during April, we have seen a noticeable drop in the number of vehicles on Darley Avenue. 


The total number of cars on Darley Avenue this month was 22952, which is down 56% from last month.


The busiest day for cars was Tuesday 18 May with 1087 cars recorded.


The quietest day for cars was Monday 3 May with 445 cars recorded.


The average morning peak hour for cars was 08:00-09:00. The average afternoon peak hour was 15:00-16:00.

Air Quality & Pollution Readings – Headline information


Pollution levels throughout May were Low


19 days registered Level 2 on the Air Quality Index, with 12 registering Level 3.


There were 5 more days on Level 3 than in April


Source: **please note that all figures are indicative only and may vary up to 10%. Figures for pedestrians do not distinguish between individuals and groups – i.e a group of 3 people walking together will be counted as 1. For a more detailed break down visit or


Air Quality Index Table 

Source: The index is made up of readings taken from an EarthSense Zephr air quality monitor installed on Darley Avenue. The index is worked out by measuring Nitrogen Monoxide (NO), Nitrogen Dioxide (NO2), Ozone (O3) and Particulate Matters (PM1, PM2.5 & PM10). We then used DEFRA’s Daily Air Quality Index to determine the result.

Four Banks:

Air Quality Index scale



On Tuesday 18 May 2021 we recorded the most number of cars on Darley Avenue with peaks at 8-9am and 4-5pm.

If we look at pollution levels for this time, we can see spikes in pollutants at this time. We also see an increase in ozone (O3) and a drop in nitrogen dioxide (NO2) during the daytime. This is most likely due to natural sunlight breaking nitrogen down into ozone.

About Air Quality and Car Usage


It’s difficult to show a direct link between car usage and air quality because many factors come into play, including temperature, the weather and other environmental conditions. Cars are also not the only cause of such pollutants.


However, we are able to illustrate some short-term effects on a very localised level. The graph below shows pollution levels on Darley Avenue on 7 April 2021, which is when the first in-person traffic survey was carried out. 


At 7.30am you can see a spike in NO and NO2, and levels of Particulate Matter (PM). From being onsite, we were able to observe a car idling its engine on the roadside at this time. We can see similar spikes on Darley Avenue, particularly in the morning around 8-9am, which is also the average morning peak for car traffic at this time.

However, it is worth noting that we do not always see the same spikes in the afternoon peak and are recording overnight peaks too. Again, this could be due to a number of environmental or behavioural factors, such as different vehicle types or home heating, weather conditions etc.


Glossary and other useful information


AQIAir quality index. This tells you levels of air pollution and can provide recommendations about actions and health advice. There are various indexes available but in the UK the most common used is the Defra Daily Air Quality Index. 

The index is based on concentrations of various pollutants, which are broken down into various index levels, like in the table below. Different averaging periods are given depending on the pollutant. The overall index given is whichever is highest level.


µm – micrometre. Measurements for the various air pollutants are given in micrometres (µm). 

1µm = 0.001mm.


NO – Nitrogen Monoxide or Nitric Oxide. A colourless gas, Is not considered hazardous to health at ambient temperature.


NO2 – Nitrogen Dioxide – a reddish, brown gas, considered a primary air pollutant. In sunny, dry conditions, NO2 can break down and release an oxygen ion and cause an increase in ozone (O3).


O3 – Ozone – considers a secondary pollutant. At ground level, ozone can contribute to respiratory problems.


Particulate Matter (PM) – describes the mixture of liquid and solids found in the air, such as dust or ash. PM measurements are given based on the diameter or width of the particle.


PM1 – means the mass per cubic metre of air with particles of a diameter less that 1 micrometres (µm)


PM2.5 – means the mass per cubic metre of air with particles of a diameter less than 2.5 micrometres (µm)


PM10 – means the mass per cubic metre of air with particles of a diameter less than 10. micrometres (µm)