a system and method for collecting sub - hourly ambient particulate matter samples at flow rates of 170 - 260 l / min is suitable for either on - or off - line near - real - time multielement analysis by graphite furnace atomic absorption spectrometry and other techniques for which a sample in slurry form is advantageous . condensational growth of water vapor was used to grow fine particles by steam injection . the grown droplets are concentrated using a virtual impactor , then separated from the airstream using a real impactor . the particles are collected in a liquid slurry which is hydraulically delivered to sample vials every 30 minutes for offline analysis , or directly delivered into the graphite furnace for atomic absorption spectrometry analysis .