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Keywords:

  • Arctic aerosol number concentration;
  • aerosol variability;
  • biomass burning

Abstract

The objective of this work is to investigate the variability in the aerosol particle number concentration in Arctic spring. The Indirect and Semi-Direct Aerosol Campaign (ISDAC) was conducted during April 2008 in the vicinities of Fairbanks and Barrow, Alaska. Aircraft-based measurements of total aerosol particle number concentration (Na) in the size range of 0.12–3 µm diameter were obtained using a passive cavity aerosol spectrometer probe (PCASP-100X). The analysis considers Na during cloud-free periods in biomass burning (BB) and non-BB aerosol loading scenarios, the latter including background cases and cases with elevated concentration in layers. The BB cases had air masses originating mainly from Russian and Asian forest and crop fires, whereas the non-BB cases originated predominantly from Arctic or oceanic regions. The average Na for all non-BB cases was 127 cm−3, while that for all BB cases was Na = 720 cm−3. These estimates do not, however, capture the details of aerosol particle layers encountered during most flights. Variability in Na was considered for constant altitude (horizontal) flight legs ranging from 50 to 650 km in length, as well as for vertical flight profiles up to 7 km above sea level. When aerosol particle layers were encountered, Na rapidly increased from 20 to 550 cm−3, and reached up to 2200 cm−3 within air masses dominated by BB plumes. The observed variability in Na may have important implications for estimating cloud microphysical properties as well as estimates of particle properties used in global climate model simulations, because averaging over large space- or time-scales may not represent real atmospheric conditions. The analysis demonstrates the difficulty in interpreting average aerosol particle characteristics along longer flight legs, particularly during cases with higher particle loading that varies over shorter distance scales and time periods. Copyright © 2012 Royal Meteorological Society and Crown in the right of Canada.