RESUMEN
New particle formation (NPF) was investigated at a coastal background site in Southwest Spain over a four-year period using a Scanning Particle Mobility Sizer (SMPS). The goals of the study were to characterise the NPF and to investigate their relationship to meteorology, gas phase (O3, SO2, CO and NO2) and solar radiation (UVA, UVB and global). A methodology for identifying and classifying the NPF was implemented using the wind direction and modal concentrations as inputs. NPF events showed a frequency of 24% of the total days analysed. The mean duration was 9.2±4.2 h. Contrary to previous studies conducted in other locations, the NPF frequency reached its maximum during cold seasons for approximately 30% of the days. The lowest frequency took place in July with 10%, and the seasonal wind pattern was found to be the most important parameter influencing the NPF frequency. The mean formation rate was 2.2±1.7 cm(-3) s(-1), with a maximum in the spring and early autumn and a minimum during the summer and winter. The mean growth rate was 3.8±2.4 nm h(-1) with higher values occurring from spring to autumn. The mean and seasonal formation and growth rates are in agreement with previous observations from continental sites in the Northern Hemisphere. NPF classification of different classes was conducted to explore the effect of synoptic and regional-scale patterns on NPF and growth. The results show that under a breeze regime, the temperature indirectly affects NPF events. Higher temperatures increase the strength of the breeze recirculation, favouring gas accumulation and subsequent NPF appearance. Additionally, the role of high relative humidity in inhibiting the NPF was evinced during synoptic scenarios. The remaining meteorological variables (RH), trace gases (CO and NO), solar radiation, PM10 and condensation sink, showed a moderate or high connection with both formation and growth rates.