Multiple daytime nucleation events in semi-clean savannah and industrial environments in South Africa: analysis based on observations

Abstract

Recent studies have shown very high frequencies of atmospheric new particle formation in different environments in South Africa. Our aim here was to investigate the causes for two or three consecutive daytime nucleation events, followed by subsequent particle growth during the same day. We analysed 108 and 31 such days observed in a polluted industrial and moderately polluted rural environments, respectively, in South Africa. The analysis was based on two years of measurements at each site. After rejecting the days having notable changes in the air mass origin or local wind direction, i.e. two major reasons for observed multiple nucleation events, we were able to investigate other factors causing this phenomenon. Clouds were present during, or in between most of the analysed multiple particle formation events. Therefore, some of these events may have been single events, interrupted somehow by the presence of clouds. From further analysis, we propose that the first nucleation and growth event of the day was often associated with the mixing of a residual air layer rich in SO₂ (oxidized to sulphuric acid) into the shallow surface-coupled layer. The second nucleation and growth event of the day usually started before midday and was sometimes associated with renewed SO₂ emissions from industrial origin. However, it was also evident that vapours other than sulphuric acid were required for the particle growth during both events. This was especially the case when two simultaneously growing particle modes were observed. Based on our analysis, we conclude that the relative contributions of estimated H₂SO₄ and other vapours on the first and second nucleation and growth events of the day varied from day to day, depending on anthropogenic and natural emissions, as well as atmospheric conditions

Source apportionment of wide range particle size spectra and black carbon collected at the airport of Venice (Italy)

“…Nucleation range particles show an evident increase during daytime, which is broadly comparable with the diurnal pattern in solar irradiance. Similar diurnal cycles have been observed in other studies (e.g., Kulmala and Kerminen, 2008;Chen et al, 2011;Hirsikko et al, 2013) and have been attributed to nucleation events driven by photochemical reactions and possibly assisted by turbulent mixing in the atmosphere (Janssen et al, 2012). However, the diurnal cycle of nucleation particles is also very similar to that of air traffic intensity.…”

Regional effect on urban atmospheric nucleation

“…The overall treatment of the measured DMPS data was performed according to the procedure protocol recommended by Kulmala et al (2012). The individual size distributions were fitted by lognormal functions using the DoFit algorithm (Hussein et al, 2004). The identification of an NPF and subsequent particle growth process was accomplished by using the algorithm of Dal .…”

Seasonal influences on surface ozone variability in continental South Africa and implications for air quality

“…Anthropogenic emissions from household combustion, traffic and industry in the wider region have a strong influence on the measurement site (Venter et al, 2012). Data was collected for a period from 8 February 2008 to 16 May 2010 5 and has been previously used in other studies (Venter et al, 2012;Vakkari et al, 2013;Petäjä et al, 2013;Hirsikko et al, 2012;Hirsikko et al, 2013).…”