Polluted Troposphere - Ionisation as a precursor to aerosol formation

The Polluted Troposphere Programme is a 5-year NERC thematic research programme which is centred upon the study of polluted boundary layer air and its transport to the free troposphere. The programme focusses on the regional scale, defined as intermediate between urban and hemispheric.

The Polluted Troposphere programme started in 2001 and will end in 2006. It has run a single round of awards, through which six projects have been funded.

• Tropospheric ORganic CHemistry experiment (TORCH).
• CLOud Processing of regional Air Pollution advecting over land and sea. (CLOPAP)
• Transport and mixing in fronts.
• Ionisation as a precursor to aerosol formation.
• Advanced GC-MS technology for observing OVOCs and NMHCS in the polluted troposphere.
• Aircraft Measurement of Chemical Processing and Export fluxes of Pollutants over the UK (AMPEP).

Ionisation as a precursor to aerosol formation is a NERC Polluted Troposphere Research Programme project (Round 1 - NER/T/S/2002/00150 - Duration 2002 - 2005) and is led by Dr RG Harrison, University of Reading.

Formation of ultrafine particles from molecular cluster ions in the atmosphere has recently been shown to occur in urban air, from both experimental findings and theoretical considerations. Ion-induced (or mediated) aerosol formation is currently neglected, despite the considerable variability known in atmospheric ions. Ionisation in the atmosphere is ubiquitous, arising from cosmic rays and natural radioactivity, with a further contribution from nuclear reprocessing. The efficiency of ion to particle conversion is sensitive to gas composition and condensable vapour supply. The work will measure ion- induced ultrafine particle production in surface air, combining ion and aerosol data. Existing ion-aerosol theory will be extended to include particle production from ions, to assess the significance for clouds of additional condensation nuclei.

These data are now publicly accessible via the BADC website and FTP server.

Surface level measurements of background ion production rates and small ion concentrations were made at the Weybourne Atmospheric Observatory on the Norfolk coast during the TORCH 2 campaign of May/June 2004 and at the University of Reading meteorological field site, where measurements of ion properties are continuing. Weybourne is an excellent site for ion-aerosol studies, as it experiences a wide range of aerosol and ion production rates, as the wind direction and air masses change. Continental air masses are exposed to greater ion production rates and a greater abundance of pollutant aerosol compared with marine air. The influence of aerosol concentration on ion removal, as determined experimentally, has been compared with ion-aerosol theory: the experimental data also shows changes in the ion properties that appear to be linked to the aerosol concentration.

The photograph shows the experimental arrangement at Weybourne with, a) Four PIMS instruments (sampling tubes vertical on the left of the mast) for measuring bipolar ion concentrations and two Geiger counters (one further Geiger counter was mounted remotely) to measure ion production rate and 16 channel laptop logger box. Close-ups of the Geiger counters and the PIMS instruments deployed at the University of Reading meteorological field site are shown in b) and c) respectively.

a)

b) c)

Data collected for this project can be found in the Polluted Troposphere data directory. In accordance with the Polluted Troposphere Data Protocol, which aims at encouraging rapid dissemination of scientific results while simultaneously protecting the rights of individual scientists, this data is now publicly available.

The data are stored in NetCDF and NASA-Ames formats. Filenames follow the BADC filename convention.

Users are requested to contact the project PI prior to publishing any work based on or using this data.

• Polluted troposphere six project descriptions
• The Data Management Plan is available in PDF or Word formats.
• Polluted Troposphere Data Protocol (also available in PDF and Word formats.)
• NASA-Ames data and metadata format
• NetCDF format and CF metadata conventions.

• An online workspace has been created for the Polluted Troposphere participants in order to ease cross-project coordination and exchange of views, information and preliminary data. The workspace is only accessible to the programme participants who have been invited. If you are a Polluted Troposphere scientist and have not been invited to access the workspace, please contact the BADC helpdesk.

• The programme science and implementation plans, project summaries, news, announcements of opportunities, as well as meeting reports and presentations are available from the Polluted Troposphere Web site at NERC.
• The Universities Facility for Atmospheric Measurement (UFAM) Web site.
• The Facility for Airborne Atmospheric Measurements (FAAM) Web site.

• Details of publications arising from this project can be found on the PT publications page.

Natural Environment Research Council, [Harrison, R.G.; Wilding, R.]. Polluted Troposphere - Ionisation as a precursor to aerosol formation, [Internet]. NCAS British Atmospheric Data Centre, 2007-, Date of citation. Available from http://badc.nerc.ac.uk/view/badc.nerc.ac.uk__ATOM__dataent_11738870972217350

• If you have queries about these pages or about obtaining Polluted Troposphere data from the BADC then you should contact BADC Support. Your query should be answered within one working day. When follow-up work is required, the BADC support will carry out the work as quickly and efficiently as possible, and in any case, the user will be kept informed of progress.
• The Programme Superintending Officer is Dr. Ruth Kelman (NERC, Swindon).
• The chairman of the Programme Steering Committee is Prof Gerard Jennings (Galway, Ireland).