Air monitoring is the key to understanding how clean the air is in a particular area. In order to do this, each state must operate a network of monitoring stations.
Since July 1967, the Division for Air Quality (DAQ) has operated an air quality monitoring network in Kentucky. The 2014 network includes 34 monitoring stations in 26 counties; this total includes monitors operated by the Louisville Metro Air Pollution Control District (LMAPCD) and the National Park Service (NPS) at Mammoth Cave. In total, the network consists of 142 instruments including 16 meteorological stations.
According to federal regulation (40 CFR Part 58, Appendix D), the ambient air monitoring network must be designed to meet three basic air monitoring objectives:
- The network must provide air pollution data to the general public in a timely manner.
- The network must support compliance with national ambient air quality standards (NAAQS) and emissions strategy development.
- The network must support air pollution research studies.
Locations of ambient air monitoring stations are selected in accordance with EPA regulations (40 CFR 58, Appendix D). In general, monitors are placed in densely populated areas or near sources of pollution, whether it’s a busy highway or a stationary source with a smokestack. Each year, the site locations are reviewed to ensure that adequate coverage is being provided and regulatory requirements are met.
So, how does an air monitor work? It depends on the pollutant. Air samples may be collected in a canister, drawn through a filter, or continuously sampled and analyzed. Continuous air monitors operate 24/7, continuously analyzing the air for specific pollutants. Manual samplers require air samples and filters to be collected and analyzed in a lab.
Let’s take a closer look at how the division monitors one of those pollutants: particulate matter.
The Clean Air Act requires states to monitor for two kinds of particulate matter:
PM2.5 and PM10. PM2.5 is a mixture of solid particles and liquid droplets that are 2.5 microns or smaller in size, while PM10 is a mixture of solid particles and liquid droplets that are 10 microns or smaller in size. So if you think about it, PM2.5 is technically a component of PM10.
Sources of particulate matter include construction activities (fine dust), agricultural practices, power plants, wood burning, industrial processes, and fuel combustion. Fine particulates can also be formed in the atmosphere when gases are transformed through chemical reactions.
Most PM10 samplers are the intermittent type that operates for 24 hours, every sixth day. Some intermittent samplers may operate on a more frequent schedule in order to investigate localized concerns. Intermittent samplers operate by drawing a measured volume of air through a pre-weighed filter over a 24-hour period. Before reaching the filter, the air passes through an impaction chamber where larger particles fall out of the air stream while particles ten microns and smaller pass on to the sample filter where they are collected.
After completion of the sample run, the filter is removed from the sampler and reweighed to determine the mass of the particulates collected. Sample results are entered manually into a data storage system.
The network also includes continuously operating PM10 samplers that provide results daily. These samplers determine sample weights electronically, transmitting the results by telemetry into an automated system.
Next week we’ll explore how PM2.5 is monitored – and what science can tell us about its composition.