Black carbon — The dark side of radiative forcing

Paul Buckley is a Postgraduate Scholar in the Department of Chemistry and Environmental Research Institute at University College Cork. In 2015, Paul was awarded an Environmental Protection Agency Postgraduate Scholarship, allowing him to carry out his research project, entitled “Nature and Origin of Black Carbon in Ireland,” in the Centre for Research into Atmospheric Chemistry. His blog is part of our theme for the month of April, “Planes, Trains and Automobiles.”

One of the best aspects about researching the topic of air quality is that everyone you meet has an opinion, and you can have a conversation with most people about it. The questions I get asked most frequently are “What is black carbon?”, “Where does it come from?”, and of course “How does it affect me?” Hopefully I can answer these questions for you here.

Black carbon (BC) is another name for soot, something we are all very used to seeing in fire places or on car exhausts. However, each individual soot particle is extremely small, invisible to our eyes. Even though they are miniscule, the large numbers of these particles combine to produce some extreme effects.

Firstly, BC is a major positive radiative forcing agent in our atmosphere. This, despite what the name may suggest, is not a good thing. In fact, it means that BC contributes in a big way to global warming. Today, BC particles are now recognised as the second most important positive forcing agent, behind the much more famous carbon dioxide.

Secondly, BC particles can also have some serious health effects. Do you know anyone with asthma or other respiratory problems? Well, BC particles are small enough to penetrate deep into our lungs and can exacerbate conditions like asthma upon exposure. Some BC particles are even small enough to enter the blood stream and be transported around the body. Depending on where they are dropped off they can do serious damage ranging from heart disease to interfering with organ functions.

With this in mind, it is clear that reducing BC concentrations will be beneficial for climate, air quality and human health. My work is focused on identifying the sources of BC in Ireland, with the aim of informing policy and shaping regulations in the future. My research is tied to two Environmental Protection Agency (EPA) projects based on quantifying the contribution of domestic solid fuel burning to pollution in residential areas and also identifying seasonal variations in BC emissions.

These field measurements have shown that extremely high levels of BC occur in the evening during winter months in Irish towns outside of the smoky coal ban (Killarney, Enniscorthy, and Birr). Concentrations of up to 65 µg/m³ were observed for short periods, which are over 100 times the background level, observed on “unpolluted” days. In Enniscorthy, the daily average for black carbon in January was 3.99 µg/m³, twice the concentration observed in Paris during the same month. Importantly, our instruments show that the peaks in BC were due to burning of coal, peat and wood for home heating. Dublin shows higher background levels of BC due to traffic emissions, but a sizeable increase is observed in during winter months which is also attributed to solid fuel burning.

In conclusion, BC has a huge impact on the environment and on our health. My work shows that domestic solid fuel burning is the major source of this pollution and hopefully, the results will inform and help shape air quality legislation over the coming years.