The optical properties of black carbon

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An aerosol particle is so small that you could line up one hundred in the width of a human hair. It can float in the air almost undetected. These particles are important for human health: for example pollen causes hay fever. Asbestos, which was used in buildings built in the 1960s can generate an aerosol when disturbed that, if inhaled, can lead to lung cancer (in Britain around 3500 people die prematurely each year because of asbestos aerosols). Aerosols also play an important role in climate change. Most people are aware that global warming is due to gases such as carbon dioxide released into the atmosphere, but aerosols also play an important role. Aerosols present in the atmosphere tend to reflect sunlight back into space, causing cooling of the Earth's atmosphere. Yet some aerosols, for example from fires and old diesel cars, are made from carbon and actually absorb the Sun's light. This warms the atmosphere. Aerosols also have an indirect effect on the climate: for example each water droplet in a cloud is normally formed around an aerosol particle, so more aerosols in the atmosphere will also affect how clouds form. Despite all that is known about aerosols their overall effect on global warming is uncertain. It is unclear if they cool or heat the Earth. This is particularly true for the light absorbing carbon aerosols. This project measures the optical properties that determines how much warming black carbon aerosols contribute, and how this changes as the aerosol ages. Many countries (e.g., China) are experiencing extended periods of economic and industrial growth that is likely to continue in future decades. This growth is accompanied by large increases in emissions of trace gases and particles, with serious implications for regional air quality and global climate. The information we gain will allow the government to regulate aerosol air pollution, hence improving air quality and public health.