Dynamic and timing properties of new aerosol particle formation and consecutive growth events

Abstract

Dynamic properties, i.e. particle formation rate J6 and particle diameter growth rate GR10, and timing properties, i.e. starting time (t1) and duration time interval (Δt) of 247 quantifiable atmospheric new aerosol particle formation (NPF) and growth events identified in the city centre and near-city background of Budapest over 6 full measurement years, together with related gas-phase H2SO4 proxy, condensation sink (CS) of vapours, basic meteorological data and concentrations of criteria pollutant gases were derived, evaluated, discussed and interpreted. In the city centre, nucleation ordinarily starts at 09:15 UTC + 1, and it is maintained for approximately 3 h. The NPF and growth events produce 4.6 aerosol particles with a diameter of 6 nm in 1 cm3 of air in 1 s and cause the particles with a diameter of 10 nm to grow at a typical rate of 7.3 nm h−1. Nucleation starts approximately 1 h earlier in the near-city background, and it shows substantially smaller J6 (with a median of 2.0 cm−3 s−1) and GR10 values (with a median of 5.0 nm h−1), while the duration of nucleation is similar to that in the centre. Monthly distributions of the dynamic properties and daily maximum H2SO4 proxy do not follow the mean monthly pattern of the event occurrence frequency. The factors that control the event occurrence and that govern the intensity of particle formation and growth are not directly linked. New particle formation and growth processes advance in a different manner in the city and its close environment. This could likely be related to diversities in atmospheric composition, chemistry and physics. Monthly distributions and relationships among the properties mentioned provided indirect evidence that chemical species other than H2SO4 largely influence the particle growth and possibly atmospheric NPF process as well. The J6, GR10 and Δt can be described by a log-normal distribution function. Most extreme dynamic properties could not be explained by available single or compound variables. Approximately 40 % of the NPF and growth events exhibited broad beginning, which can be an urban feature. For doublets, the later onset frequently shows more intensive particle formation and growth than the first onset by a typical factor of approximately 1.5. The first event is attributed to a regional type, while the second event, superimposed on the first, is often associated with subregional, thus urban NPF and growth processes.