Number concentrations of atmospheric aerosol particles were measured by aflow-switching type differential mobility particle sizer in an electricalmobility diameter range of 6–1000 nm in 30 channels near central Budapestwith a time resolution of 10 min continuously from 3 November 2008 to 2November 2009. Daily median number concentrations of particles varied from3.8 × 10 to 29 ×10 cm with a yearly medianof 11.8 × 10 cm. Contribution of ultrafine particles tothe total particle number ranged from 58 to 92% with a mean ratio andstandard deviation of (79 ± 6)%. Typical diurnal variation of theparticle number concentration was related to the major emission patterns incities, new particle formation, sinks of particles and meteorology. Shapesof the monthly mean number size distributions were similar to each other.Overall mean for the number median mobility diameter of the Aitken andaccumulation modes were 26 and 93 nm, respectively, which are substantiallysmaller than for rural or background environments. The Aitken andaccumulation modes contributed similarly to the total particle numberconcentrations at the actual measurement location. New particle formationand growth unambiguously occurred on 83 days, which represent 27% of allrelevant days. Hence, new particle formation and growth are not rarephenomena in Budapest. Their frequency showed an apparent seasonal variationwith a minimum of 7.3% in winter and a maximum of 44% in spring. Newparticle formation events were linked to increased gas-phase HSOconcentrations. In the studied area, new particle formation is mainlyaffected by condensation sink and solar radiation. The formation processseems to be not sensitive to SO, which was present in a yearly medianconcentration of 6.7 μg m. This suggests that the precursor gaswas always available in excess. Formation rate of particles with a diameterof 6 nm varied between 1.65 and 12.5 cm s with a mean andstandard deviation of (4.2 ± 2.5) cm s. Seasonal dependencyfor the formation rate could not be identified. Growth curves of nucleatedparticles were usually superimposed on the characteristic diurnal pattern ofroad traffic direct emissions. The growth rate of the nucleation mode with amedian diameter of 6 nm varied from 2.0 to 13.3 nm h with a mean andstandard deviation of (7.7 ± 2.4) nm h. There was an indicativetendency for larger growth rates in summer and for smaller values in winter.New particle formation events increased the total number concentration by amean factor and standard deviation of 2.3 ± 1.1 relative to theconcentration that occurred immediately before the event. Several indirectevidences suggest that the new particle formation events occurred at leastover the whole city, and were of regional type. The results and conclusionspresented are the first information of this kind for the region overone-year long time period.
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