title: Analysis of organic aerosols using a micro-orifice volatilization impactor coupled to an atmospheric-pressure chemical ionization mass spectrometer.
abstract: We present the development and characterization of a combination of a micro-orifice volatilization impactor (MOVI) and an ion trap mass spectrometer (IT/MS) with an atmospheric-pressure chemical ionization (APCI) source. The MOVI is a multi-jet impactor with 100 nozzles, allowing the collection of aerosol particles by inertial impaction on a deposition plate. The pressure drop behind the nozzles is approximately 5%, resulting in a pressure of 96kPa on the collection surface for ambient pressures of 101.3 kPa. The cut-point diameter (diameter of 50% collection efficiency) is at 0.13 microm for a sampling flow rate of 10 L min(-1). After the collection step, aerosol particles are evaporated by heating the impaction surface and transferred into the APCI-IT/MS for detection of the analytes. APCI was used in the negative ion mode to detect predominantly mono- and dicarboxylic acids, which are major oxidation products of biogenic terpenes. The MOVI-APCI-IT/MS instrument was used for the analysis of laboratory-generated secondary organic aerosol (SOA), which was generated by ozonolysis of alpha-pinene in a 100 L continuous-flow reactor under dark and dry conditions. The combination of the MOVI with an APCI-IT/MS improved the detection Limits for small dicarboxylic acids, such as pinic acid, compared to online measurements by APCI-IT/MS. The Limits of detection and quantification for pinic acid were determined by external calibration to 4.4 ng and 13.2 ng, respectively. During a field campaign in the southern Rocky Mountains (USA) in summer 2011 (BEACHON-RoMBAS), the MOVI-APCI-IT/MS was applied for the analysis of ambient organic aerosols and the quantification of individual biogenic SOA marker compounds. Based on a measurement frequency of approximately 5 h, a diurnal cycle for pinic acid in the sampled aerosol particles was found with maximum concentrations at night (median: 10.1 ngm(-3)) and minimum concentrations during the day (median: 8.2 ng m(-3)), which is likely due to the partitioning behavior of pinic acid and the changing phase state of the organic aerosol particles with changing relative humidity.
authors.forename: Martin
authors.initials: M
authors.lastname: Brüggemann
authors.forename: Alexander Lucas
authors.initials: AL
authors.lastname: Vogel
authors.forename: Thorsten
authors.initials: T
authors.lastname: Hoffmann
mesh_terms: D000336:Aerosols / Q000737:chemistry*; D001274:Atmospheric Pressure; D000081008:Bicyclic Monoterpenes; D002264:Carboxylic Acids / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D007477:Ions / Q000032:analysis; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D039821:Monoterpenes / Q000737:chemistry; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry; D013729:Terpenes / Q000032:analysis / Q000737:chemistry; D014835:Volatilization
chemical_list: D000336:Aerosols; D000081008:Bicyclic Monoterpenes; D002264:Carboxylic Acids; D007477:Ions; D039821:Monoterpenes; D013729:Terpenes; D010126:Ozone; C005451:alpha-pinene