Impact from local sources and variability of fine particle number concentration in a coastal sub-urban site

Particle number (PN) concentration was measured in coastal sub-urban site in Crete, Greece, between September 2013 and August 2014. Outdoor data were obtained for 173 sampling days with particle number size distribution measured in the size range 5.5–350.4 nm. Ambient concentrations varied considerably during the campaign with local sources playing a dominant role on temporal fluctuations. In particular, domestic heating was identified as the main anthropogenic activity that produces ultrafine particles with the higher PN concentrations measured on cold months among the measured periods. In turn, investigation of the impact of wind direction has shown that east direction was associated with elevated ultrafine PN concentrations, whilst, the monthly variability during warm periods was linked with the frequency of east-originated winds. Elevated concentrations were attributed to aviation/shipping emissions transported from the nearby airport and port. On the contrary, city-originated (southwest) winds were not associated with a pattern of increased ultrafine PN concentrations. In addition, diurnal profiles demonstrated that local traffic during rush hours (06:00–09:00 and 19:00–22:00) is responsible for increased PN concentrations for these parts of the day. However, the influence from vehicular emissions to ambient PN concentrations was lower compared to emissions from domestic heating. The seasonal variability between weekends/weekdays was also associated with traffic profile. Overall, 23 new particle formation (NPF) events were identified through the present campaign with growth rate (GR) vary between 0.75 and 5.87 nm/h and formation rate (JD) vary between 0.0005 and 0.2454 cm⁻³ s⁻¹. The majority of NPF events started in the morning and after rush hours highlighting the role played by precursor gases from traffic emissions for urban sites. Moreover, the majority of the NPF events presented a west/north/northwest prevailing wind direction suggesting that fresh sea breeze air is a key factor for the formation of new particles in the under study site. Lastly, moderate positive correlations with meteorological variables found between temperature and GR, relative humidity and JD, solar radiation and GR whereas moderate negative correlation found between wind speed and JD.