Interpretation of particle number size distributions measured across an urban area during the FASTER campaign

Abstract

Abstract. 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−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. 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 CPC∕SMPS and CPC∕BC 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.

Analysis of New Particle Formation (NPF) Events at Nearby Rural, Urban Background and Urban Roadside Sites

“…In this study the events of class Ia are only considered as being the most suitable for analysing case studies of NPF events. This analysis took account of the fact that nanoparticle emissions from Heathrow Airport affect size distributions at London sites (Harrison et al, 2018), and such primary emission influences were not included as NPF events.…”

Traffic-induced multicomponent ultrafine particle microphysics in the WRF v3.6.1 large eddy simulation model: General behaviour from idealised scenarios at the neighbourhood-scale

“…In this study, we introduce a BASE case scenario and the settings are as follows. The emission factor for total UFP number is 7.93×10 13 particles vehicle -1 km -1 , which is based on the value from Jones and Harrison (2006) with a correction factor for the year of 2017 derived from an analysis of measurement data (Harrison et al, 2019). The traffic activity is specified as 3740 vehicle hour -1 at a heavily trafficked street (Marylebone Road) for the 180º wind sector during the campaign in London (Harrison et al, 2019).…”

“…The traditional assumption of a one box model for a compartmentalised canyon would typically under-predict the UFP number concentration in the lower canyon compared with the proposed two-box model. The traffic-generated nanoparticles vented out from an urban street network, which may be simulated by a street canyon box model (Nikolova et al, 2016), could be evaporated to smaller particles while they are transported during neighbourhood scale dispersion (Dall'Osto et al, 2011;Harrison et al, 2019).…”

review Comment on acp-2020-1282

“…Previously, particle size distributions have been measured in different urban environments, such as London (Bousiotis et al, 2019;Harrison et al, 2019;Hofman et al, 2016), Stockholm (Mårtensson et al, 2006), Innsbruck (Deventer et al, 2018), Los Angeles (Zhu et al, 2002), Beijing (Zhou et al, 2020), Shanghai (Xiao et al, 2015), and Helsinki Ripamonti et al, 2013). In the Helsinki area, the focus of the research has been either on NPF (Hussein et al, 2008(Hussein et al, , 2009 or the primary particle emissions (Hietikko et al, 2018;Ripamonti et al, 2013;Rönkkö et al, 2017).…”