Evaluating Particulate Matter in the Air - Chromatography Investigates

Air quality and pollution is a topic that always seems to be in the news. And with good reason as it is estimated that poor air quality contributes to almost 500.000 premature deaths across Europe each year. There are several different categories of air pollutants, in fact, the US Environmental Protection Agency (EPA) lists six different common air pollutants under the Clean Air Act.

One of those criteria air pollutants is known as particulate matter or PM. PM is itself composed of different compounds that are linked to different sources and different toxicity. It is important that we can identify the compounds in a particular PM to understand its source and possible hazards associated with it. This is the rationale behind research recently published by the University of Ruse in Bulgaria who used gas chromatography-mass spectromentry to analyse and identify PM components.

Particulates in the air

The US EPA lists six groups of air pollutants; ground-level ozone, particulate matter, carbon monoxide, lead, sulphur dioxide and nitrogen dioxide. All of these pollutants are hazardous in their own way. Particulate matter contains microscopic solids or liquid drops that are so small they can be inhaled and get deep into the lungs and the bloodstream. Particulate matter is divided into two categories: PM₁₀ contains particles smaller than 10 micrometres in diameter and PM_2.5 contains particles less than 2.5 micrometres in diameter - these finer particles pose the most significant risk to health.

What’s in the particles?

In recent years researchers have focussed on trying to identify the chemical composition of the particles. Knowing what the composition of the particles are would allow regulators to target the source of the particles and also know what the specific hazards are associated with the particles. Several compounds have been identified including aldehydes, ketones, dioxins, benzene and PAHs.

PAHs (polycyclic aromatic hydrocarbons) are a group of hundreds of chemical compounds that are associated with incomplete combustion of organic matter. They are known to have carcinogenic and mutagenic properties. The European Union uses a PAH known as benzo[a]pyrene as a marker for the carcinogenic risk associated with a PAH.

Chromatography analyses the PM

But PAHs occur at very low levels in PM making determination of PAHs difficult. The research team from the University of Ruse set out to develop an analytical method for the determination of PAHs in PM₁₀ and PM_2.5. The method they developed used gas chromatography-mass spectrometry - the latest developments in chromatography are discussed in the article, SFC/SFE 2019:  Pushing the Limits.

The method developed by the team was validated using a spiked sample containing 19 different PAHs and could be described as accurate and precise. The team then tried the method on actual samples and found that the method could detect levels of PAHs in PM from air samples. The majority of the samples had PAHs within current limits.