Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition

Abstract

An improved particle-into-liquid sampler (PILS) has proven successful in both ground-based and aircraft experiments for rapid measurements of soluble aerosol chemical composition. Major modifications made to the prototype PILS (Aerosol Sci. Technol. 35 (2001) 718) improve particle collection at higher sample flow (15–17 l min −1) while maintaining minimal sample dilution. Laboratory experiments using a fluorescent calibration aerosol aided in designing the present system and characterized the PILS collection efficiency as a function of particle size. Collection efficiency for particle diameters D p between 0.03 and 10 μm is greater than 97%. In addition, the instrument now samples at low pressures (0.3 atmosphere) necessary for airborne measurements up to approximately 8 km in altitude. An ion chromatograph (IC) is coupled to the PILS for direct on-line analysis of the collected sample (hence the name ‘PILS-IC’). Proper selection of columns and eluants allows for 3.5–4 min separation of 9 major inorganic species (Na +, NH 4 +, K +, Ca 2+, Mg 2+, Cl −, NO 3 −, NO 2 −, SO 4 2−), while acetate, formate, and oxalate, are also possible in 15 min. Any analytical technique capable of continuous online analysis of a liquid sample can be coupled to the PILS for quantitative semi-continuous measurements of aerosol composition. Changes made to the prototype are explained and data from a recent experiment are compared with standard integrated filter measurements.