Real-time secondary aerosol formation during a fog event in London
1National Centre for Atmospheric Science Division of Environmental Health and Risk Management School of Geography, Earth and Environmental Sciences University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
2National Centre for Atmospheric Science School of Earth, Atmospheric and Environmental Sciences The University of Manchester, Simon Building Oxford Road, Manchester M13 9PL, UK
*now at: Centre for Climate and Air Pollution Studies, Environmental Change Institute, National University of Ireland, Galway, Ireland
Abstract. A fog event was monitored with state-of-the art real-time aerosol mass spectrometers in an urban background location in London (England) during the REPARTEE-I experiment. Specific particle types rich in hydroxymethanesulphonate (HMS) were found only during the fog event. Formation of inorganic and organic secondary aerosol was observed as soon as fog was detected and two different mechanisms are suggested to be responsible for the production of two different types of aerosol. Nitrate aerosol is produced in the liquid phase within the droplet. Contrary to previous studies, the formation of HULIS was observed on interstitial particles rather than evaporated fog droplets, suggesting heterogeneous formation mechanisms depending on parameters other than the water content and not fully understood. Not only are secondary aerosol constituents produced during the fog event, but the primary aerosol is observed to be processed by the fog event, dramatically changing its chemical properties.