Abstract
Abstract. Ambient particle number size distributions were measured in Paris, France, during summer (1–31 July 2009) and winter (15 January to 15 February 2010) at three fixed ground sites and using two mobile laboratories and one airplane. The campaigns were part of the Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation (MEGAPOLI) project. New particle formation (NPF) was observed only during summer on approximately 50 % of the campaign days, assisted by the low condensation sink (about 10.7 ± 5.9 × 10−3 s−1). NPF events inside the Paris plume were also observed at 600 m altitude onboard an aircraft simultaneously with regional events identified on the ground. Increased particle number concentrations were measured aloft also outside of the Paris plume at the same altitude, and were attributed to NPF. The Paris plume was identified, based on increased particle number and black carbon concentration, up to 200 km away from the Paris center during summer. The number concentration of particles with diameters exceeding 2.5 nm measured on the surface at the Paris center was on average 6.9 ± 8.7 × 104 and 12.1 ± 8.6 × 104 cm−3 during summer and winter, respectively, and was found to decrease exponentially with distance from Paris. However, further than 30 km from the city center, the particle number concentration at the surface was similar during both campaigns. During summer, one suburban site in the NE was not significantly affected by Paris emissions due to higher background number concentrations, while the particle number concentration at the second suburban site in the SW increased by a factor of 3 when it was downwind of Paris.
Highlights
Urban areas in the developed and developing world have been growing annually by 0.7 % in population since 2005 and comprised approximately 54 % of the total population of the planet in 2014 (United Nations, 2014)
In this work we focus on the particle number concentrations in Paris and its surroundings during both campaigns
To investigate the impact of the emissions from the city center on number concentrations at the two satellite sites (GOLF, LHVP), the measurements were separated with respect to wind direction, excluding periods when the wind speed was below 1 m s−1 (Fig. 9)
Summary
Urban areas in the developed and developing world have been growing annually by 0.7 % in population since 2005 and comprised approximately 54 % of the total population of the planet in 2014 (United Nations, 2014). New particle formation (NPF), that is nucleation of low volatility vapors and subsequent condensational growth to larger sizes, is the major reason for high particle number concentrations (Kulmala et al, 2004). The majority of studies are based on observations from one or at most two stationary sites, assuming that these stations are representative of the area under investigation Most of these studies have found higher concentrations during winter due to both increased emissions caused by higher energy demand, and lower boundary layer height. Several modeling efforts have been conducted examining the contribution of regional sources to fine PM (Skyllakou et al, 2014) and investigating the organic aerosol sources in Paris (Couvidat et al, 2013; Zhang et al, 2013) All of these studies focused on PM mass concentration and not on particle number. The frequency and spatial characteristics of new particle formation events are investigated
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