Air quality

Air quality reports

The main pollutants of concern in Chorley are Nitrogen Dioxide (NO2) and Particulate Matter (PM). Air quality is monitored by Environmental Health, using a network of passive diffusion tubes at strategic locations across the borough. We are also trialling continuous particulate monitors to improve the monitoring programme.

The good news is that the monitoring and modelling data shows that air quality across Chorley complies with the current National Air Quality Objectives.

The legislative framework for meeting our Air Quality objectives was laid down under Part IV of the Environment Act 1995, and updated by The Environment Act 2021, which includes new responsibilities for local authorities. The National Objectives are the standards by which we monitor and assess air quality data. The data we rely on is required to meet a rigorous independent testing framework with stringent quality assurance and quality control procedures.

Annual Status Reports

Each year we produce an Annual Status Report (ASR) which is submitted to DEFRA for approval and commenting. It gives a update on our air quality and trends in Chorley, and shows the progress of measures implemented to improve air quality by Chorley Council, local partners and other agencies. They are normally publicly available by the August following the end of the previous calendar year.

You can read the most recent reports below:

Particulate Matter Report

This report is additional to the ASR and looks at the data collected from our network of particulate monitors. The first report covers data collected in 2022.

2022 Particulate Matter Report

For queries on Air Quality or to request a Word document version of the ASR please contact Environmental Health by email to contact@chorley.gov.uk.

Understanding the numbers - why do air quality figures sometimes differ dependant on what source you use?

There are many avenues to gain air quality data for specific areas.

Some people use mobile apps, others collect their own data from their own air quality monitors while others seek our data from our portal

Chorley Air Quality Monitor Data

We have a specific way in which we collect, process and publish our air quality data. This makes the figures we publish as accurate as possible.

When our air quality data is collected by our 42 diffusion tubes and 3 real time monitors across the borough, we process the raw data to collect an average figure over time, and then also apply a correction factor.

There are many things which can affect the readings of an air quality monitor. For example, the real time air quality monitors use sensitive lasers to measure the particulate pollution in the surrounding air and can be affected by external changes. An example of this could be a person or persons passing under a monitor smoking a cigarette. Our correction factor allows for these changes then takes an overall average of the levels of particulate and nitrogen pollution in the air.

Often, other sources which publish air quality data use only the raw data, with no correction factors, meaning it may not be a true reflection of the overall levels of air pollution from particulates and nitrogen oxides.

Our data is collected, processed and published in line with national guidelines.