Interpretation of particle number size distributions measured across an urban area during the FASTER campaign
<p>Particle number size distributions have been measured simultaneously by scanning mobility particle sizers (SMPSs) at five sites in central London for a 1 month campaign in January–February 2017. These measurements were accompanied by condensation particle counters (CPCs) to measure total pa...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/39/2019/acp-19-39-2019.pdf |
| Summary: | <p>Particle number size distributions have been measured simultaneously by
scanning mobility particle sizers (SMPSs) at five sites in central London for
a 1 month campaign in January–February 2017. These measurements were
accompanied by condensation particle counters (CPCs) 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
street canyon with heavy traffic, one site (Westminster University) was on a
rooftop adjacent to the Marylebone Road sampler, and 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 160 m above ground level on the
BT tower and a fifth sampler was located 4 km 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
0.04 nm s<span class="inline-formula"><sup>−1</sup></span> 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. While the SMPS total count and black carbon showed
typical traffic-dominated diurnal profiles, the CPC count data typically
peaked during night-time as did <span class="inline-formula">CPC∕SMPS</span> and <span class="inline-formula">CPC∕BC</span> ratios. This is thought to
be due to the presence of high concentrations of small particles (2.5–15 nm
diameter) probably arising from condensational growth from traffic emissions
during the cooler night-time 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
night-time, 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 22 km
from the central London sites.</p> |
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| ISSN: | 1680-7316 1680-7324 |