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To gain a better understanding on the spatiotemporal variation of ultrafine particles (UFPs) in urban environments, this study reports on the first results of a long-term UFP monitoring network, set up in Amsterdam (NL), Antwerp (BE), Leicester (UK) and London (UK). Total number concentrations and size distributions were assessed during 1–2 years at four fixed urban background sites, supplemented with mobile trailer measurements for co-location monitoring and additional short-term monitoring sites. Intra- and interurban spatiotemporal UFP variation, associations with commonly-monitored pollutants (PM, NO x and BC) and impacts of wind fields were evaluated. Although comparable size distributions were observed between the four cities, source-related differences were demonstrated within specific particle size classes. Total and size-resolved particle number concentrations showed clear traffic-related temporal variation, confirming road traffic as the major UFP contributor in urban environments. New particle formation events were observed in all cities. Correlations with typical traffic-related pollutants (BC and NO x ) were obtained for all monitoring stations, except for Amsterdam, which might be attributable to UFP emissions from Schiphol airport. The temporal variation in particle number concentration correlated fairly weakly between the four cities (r s = 0.28−0.50, COD = 0.28−0.37), yet improved significantly inside individual cities (r s = 0.59−0.77). Nevertheless, considerable differences were still obtained in terms of particle numbers (20–38% for total particle numbers and up to 49% for size-resolved particle numbers), confirming the importance of local source contributions and the need for careful consideration when allocating UFP monitoring stations in heterogeneous urban environments. [ABSTRACT FROM AUTHOR]

Atmospheric particulate pollution is a significant problem across the EU and there is concern that there may be an increasing contribution from biomass burning, driven by rising fuel prices and an increased interest in the use of renewable energy sources. This study was carried out to assess current levels of biomass burning and the contribution to total PM 10 across five sites in North-West Europe; an area which is frequently affected by poor air quality. Biomass burning was quantified by the determination of levoglucosan concentrations from PM 10 aerosol filters collected over a 14 month period in 2013/2014 and continued for a further 12 months at the UK site in Leicester. Levoglucosan levels indicated a distinct period of increased biomass combustion between November and March. Within this period monthly average concentrations ranged between 23 ± 9.7 and 283 ± 163 ng/m 3 , with Lille showing consistently higher levels than the sites in Belgium, the Netherlands and the UK. The estimated contribution to PM 10 was, as expected, highest in the winter season where the season average percentage contribution was lowest in Wijk aan Zee at 2.7 ± 1.4% and again highest in Lille at 11.6 ± 3.8%, with a PM 10 mass concentration from biomass that ranged from 0.56 μg/m 3 in Leicester to 2.08 μg/m 3 in Lille. Overall there was poor correlation between the levoglucosan concentrations measured at the different sites indicating that normally biomass burning would only affect atmospheric particulate pollution in the local area; however, there was evidence that extreme burning events such as the Easter fires traditionally held in parts of North-West Europe can have far wider ranging effects on air quality. Network validation measurements were also taken using a mobile monitoring station which visited the fixed sites to carry out concurrent collections of aerosol filters; the result of which demonstrated the reliability of both PM 10 and levoglucosan measurements. [ABSTRACT FROM AUTHOR]