Sensitivity of spatial aerosol particle distributions to the boundary conditions in the PALM model system 6.0

Mona Kurppa, Pontus Roldin, Jani Juhani Strömberg, Anna Balling, Sasu Karttunen, Heino Kuuluvainen, Jarkko V. Niemi, Liisa Pirjola, Topi Rönkkö, Hilkka Timonen, Antti Hellsten, Leena Järvi

Research output: Contribution to journalArticleScientificpeer-review

Abstract

High-resolution modelling is needed to understand urban air quality and pollutant dispersion in detail. Recently, the PALM model system 6.0, which is based on large-eddy simulation (LES), was extended with the detailed Sectional Aerosol module for Large Scale Applications (SALSA) v2.0 to enable studying the complex interactions between the turbulent flow field and aerosol dynamic processes. This study represents an extensive evaluation of the modelling system against the horizontal and vertical distributions of aerosol particles measured using a mobile laboratory and a drone in an urban neighbourhood in Helsinki, Finland. Specific emphasis is on the model sensitivity of aerosol particle concentrations, size distributions and chemical compositions to boundary conditions of meteorological variables and aerosol background concentrations. The meteorological boundary conditions are taken from both a numerical weather prediction model and observations, which occasionally differ strongly. Yet, the model shows good agreement with measurements (fractional bias <0.67, normalised mean squared error <6, fraction of the data within a factor of 2 > 0.3, normalised mean bias factor <0.25 and normalised mean absolute error factor <0.35) with respect to both horizontal and vertical distribution of aerosol particles, their size distribution and chemical composition. The horizontal distribution is most sensitive to the wind speed and atmospheric stratification, and vertical distribution to the wind direction. The aerosol number size distribution is mainly governed by the flow field along the main street with high traffic rates and in its surroundings by the background concentrations. The results emphasise the importance of correct meteorological and aerosol background boundary conditions, in addition to accurate emission estimates and detailed model physics, in quantitative high-resolution air pollution modelling and future urban LES studies.

Original languageEnglish
JournalGeoscientific Model Development
Volume13
Issue number11
Pages (from-to)5663-5685
Number of pages23
ISSN1991-959X
DOIs
Publication statusPublished - 18 Nov 2020
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 1172 Environmental sciences
  • 1171 Geosciences
  • LARGE-EDDY SIMULATION
  • AIR-POLLUTION
  • CFD SIMULATION
  • STREET CANYON
  • SURFACE-AREA
  • URBAN
  • DISPERSION
  • ENVIRONMENT
  • FLOW
  • GAS

Cite this