FEATURE One of the scientists working inside the aircraft. The smokeOdetectors Wildfires affect up to 20 million hectares of northern forests every year, and they don’t just cause damage on the ground – the plumes of gases they release are a major source of air pollution. Sarah Moller and colleagues spent part of last summer flying over Canada to learn more about them. n 13 July 2011, I was at Halifax airport in Nova Scotia, to meet the BAe-146 UK Atmospheric Research Aircraft (ARA). The ARA would fly through the plumes from Canadian forest fires, to measure and analyse the cocktail of gases and particles they release into the atmosphere. Our project studies the polluting effects of fires in boreal forests, which means the subarctic – north of 50°N. This type of fire is often called biomass burning. Locally the consequences are obvious; fires remove vegetation, endanger life and fill the air with thick black smoke. But the wider impact is harder to see. The smoke plumes contain important atmospheric pollutants – carbon monoxide (CO), nitrogen oxides (NOx), carbon dioxide (CO2), methane (CH4) and black carbon – which affect air quality and how much sunlight reaches the Earth’s surface. Prevailing winds carry pollutants from North American fires across the Atlantic Ocean to the UK and the rest of Europe, potentially affecting air quality there too. That’s where our project comes in. Our challenge is to understand how these chemicals interact as the plumes travel, and specifically how they might affect air quality in the UK. It’s not just a case of measuring the different pollutants 12 PLANET EARTH Spring 2012 Shaun Lowe/istockphoto.com