Diurnal variation of nanocluster aerosol concentrations and emission factors in a street canyon

Riina Hietikko, Heino Kuuluvainen, Roy Harrison, Harri Portin, Hikka Timonen, Jarkko V. Niemi, Topi Ronkko

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24 Citations (Scopus)
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Traffc emits a considerable amount of aerosol particles in urban areas and
has also recently been shown to be a signi_cant source of sub-3 nm particles.
In this study, the concentration of sub-3 nm particles, here referred to as
nanocluster aerosol (NCA), was continuously measured with one second resolution in a busy street canyon in the city of Helsinki, Finland, for a month
period in 2017. NCA concentrations were carefully analyzed with respect to
the time of day, the wind direction, the condensation sink, the concentration
of sub-7 nm particles, the total particle size distribution, and the CO2
concentration, from which the emission factors for the NCA were calculated.
The concentration of the NCA seemed to follow a similar trend to that of
sub-7 nm particles. Diurnal variation of the NCA concentration divided into
weekdays and weekends and sorted according to the wind direction followed
the amount traffc. The NCA concentration was at highest when wind was
blowing directly from the road, during the rush hours or when the condensation
sink calculated from the particle size distributions was low. The NCA concentration was in line with the tra_c-related nucleation mode of the size
distribution and its diurnal variation, and the NCA fraction comprised a
relatively large part of the total particle number concentration. Average
emission factors for the NCA and sub-7 nm particles were 9.36 ˑ1014 kg-1fuel
and 2.73 ˑ1015 kg-1fuel respectively. Diurnal variation of the emission factors
showed an increase in the night, which may result from a dependency of the
emission factors on traffc composition, temperature, condensation sink or
the driving mode of vehicles.
Original languageEnglish
Pages (from-to)98-106
JournalAtmospheric Environment
Early online date22 Jun 2018
Publication statusPublished - 1 Sept 2018


  • nanocluster aerosol
  • street canyon
  • urban air
  • traffic emissions


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