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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-902
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Sep 2018

Research article | 14 Sep 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Interpretation of Particle Number Size Distributions Measured across an Urban Area during the FASTER Campaign

Roy M. Harrison1,a, David C. S. Beddows1, Mohammed S. Alam1, Ajit Singh1, James Brean1, Ruixin Xu1, Simone Kotthaus2, and Sue Grimmond2 Roy M. Harrison et al.
  • 1Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
  • 2Department of Meteorology, University of Reading, Reading RG6 6BB, UK
  • aalso at: Department of Environmental Sciences/Center of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80203, Jeddah, 21589, Saudi Arabia

Abstract. Particle number size distributions have been measured simultaneously by Scanning Mobility Particle Sizers (SMPS) at five sites in Central London for a one month campaign in January–February 2017. These measurements were accompanied by condensation particle counters (CPC) to measure total particle number count at four of the sites and aethalometers measuring Black Carbon (BC) at five sites. The spatial distribution and inter-relationships of the particle size distribution and SMPS total number counts with CPC total number counts and Black Carbon measurements have been analysed in detail as well as variations in the size distributions. One site (Marylebone Road) was in a heavily-trafficked street canyon, one site (Westminster University) was on a rooftop adjacent to the Marylebone Road sampler, a further sampler was located at Regent's University within a major park to the north of Marylebone Road. A fourth sampler was located nearby at 160m above ground level on the BT tower and a fifth sampler was located 4km to the west of the main sampling region at North Kensington. Consistent with earlier studies it was found that the mode in the size distribution had shifted to smaller sizes at the Regent's University (park) site, the mean particle shrinkage rate being 0.04nms−1 with slightly lower values at low wind speeds and some larger values at higher wind speeds. There was evidence of complete evaporation of the semi-volatile nucleation mode under certain conditions at the elevated BT Tower site. Whereas SMPS total count and Black Carbon showed typical traffic-dominated diurnal profiles, the CPC count data typically peaked during nighttime as did CPC/SMPS and CPC/BC ratios. This is thought to be due to the presence of high concentrations of small particles (2.5–15nm diameter) probably arising from condensational growth from traffic emissions during the cooler nighttime conditions. Such behaviour was most marked at the Regent's University and Westminster University sites and less so at Marylebone Road, while at the elevated BT Tower site the ratio of particle number (CPC) to Black Carbon peaked during the morning rush hour and not at nighttime, unlike the other sites. An elevation in nucleation mode particles associated with winds from the West and WSW sector was concluded to result from emissions from London Heathrow Airport, despite a distance of 22km from the Central London sites.

Roy M. Harrison et al.
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Short summary
Particle number size distributions were measured simultaneously at 5 sites in London during a campaign. Observations are interpreted in terms of both evaporative shrinkage of traffic-generated particles, condensational growth probably of traffic-generated particles under cool nocturnal conditions as well as the influence of particles emitted from Heathrow Airport at a distance of about 22 kilometres. The work highlights the highly dynamic behaviour of nanoparticles within the urban atmosphere.
Particle number size distributions were measured simultaneously at 5 sites in London during a...
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