Vertical and horizontal distribution of regional new particle formation events in Madrid
Authors: Carnerero Cristina , Pérez Noemí , Reche Cristina , Ealo Marina , Titos Gloria , Lee Hong-Ku , Eun Hee-Ram , Park Yong-Hee , Dada Lubna , Paasonen Pauli , Kerminen Veli-Matti , Mantilla Enrique , Escudero Miguel , Gómez-Moreno Francisco J. , Alonso-Blanco Elisabeth , Coz Esther , Saiz-Lopez Alfonso , Temime-Roussel Brice , Marchand Nicolas , Beddows David C. S. , Harrison Roy M. , Petäjä Tuukka , Kulmala Markku , Ahn Kang-Ho , Alastuey Andrés , Querol Xavier 
Published: March 2018

Abstract. The vertical profile of new particle formation (NPF) events was studied by comparing the aerosol size number distributions measured aloft and at surface level in a suburban environment in Madrid, Spain using airborne instruments. The horizontal distribution and regional impact of the NPF events was investigated with data from three urban and suburban stations in the Madrid metropolitan area. Intensive regional NPF episodes followed by particle growth were simultaneously recorded at three stations in and around Madrid, in a field campaign in July 2016. On some days a marked decline in particle size (shrinkage) was observed in the afternoon, associated with a change in air masses. Additionally, a few nocturnal nucleation mode bursts were observed in the urban stations, which could be related to aircraft emissions transported from the airport. Considering all simultaneous diurnal NPF events registered, growth rates were significantly lower at the urban stations, ranging 2.0–3.9 nm h−1, compared to the suburban station (2.9–10.0 nm h−1). Total concentration of 9.1–25 nm particles reached 2.8 x 104 cm−3 at the urban station and 1.7 x 104 cm−3 at the suburban station, the mean daily values being 3.7 x 104 cm−3 (2.2 x 104 cm−3 at the suburban station) during event days. The formation rates of 9–25 nm particles peaked around noon and recorded a median value of 2.0 cm−3 s−1 and 1.1 cm−3 s−1 at the urban and suburban stations, respectively. The condensation and coagulation sinks presented minimum values shortly before sunrise, increasing after dawn reaching the maximum value at 14:00 UTC, with average daily mean values of 3.4 x 10−3 s−1 (2.5 x 10−3 s−1 at the suburban station) and 2.4 x 10−5 s−1, respectively, during event days. The vertical soundings demonstrated that ultrafine particles (UFP) are transported from surface levels to higher levels, thus newly-formed particles ascend from surface to the top of the mixing layer. The morning soundings revealed the presence of a residual layer in the upper levels in which aged particles (nucleated and grown on previous days) prevail. The particles in this layer also grow in size, with growth rates significantly smaller than those inside the mixed layer. Under conditions with strong enough convection, the soundings revealed homogeneous number size distributions and growth rates at all altitudes, which follow the same evolution in the other stations considered in this study. This indicates that NPF occurs quasi-homogenously in an area spanning at least 17 km horizontally. The NPF events extend over the full vertical extension of the mixed layer reaching as high as 3000 m. This can have consequences in the radiative balance of the atmosphere and affect the climate. Results also evidenced that total particle concentration in and around Madrid in summer is dominated by NPF during summer, thus it may obscure the impact of vehicle exhaust emissions on levels of UFP.