Inter-Comparisons of Major Ions and Organic Matter Using Aerodyne Aerosol Mass Spectrometer, Ion Chromatography

Filter samples (PM_1.0) were analyzed for OC and elemental carbon (EC) using a Sunset Laboratory carbon (OC/EC) analyzer following Integragency Monitoring Protected Visual Environments (IMPROVE) thermal/optical evolution protocol [28]. Major ions (NO₃⁻, SO₄²⁻ and NH₄⁺) were determined by ion chromatography (IC, 761 Compact IC, Metrohm, Switzerland). The detection limits for anions and cations were ca. 0.1 ng m⁻³. SO₄²⁻ (0.003 ng m⁻³) is detected in the field blanks whereas NO₃⁻ and NH₄⁺ are not detected in the blanks. The analytical errors in the replicate analysis of authentic standards were within 5% for major ions, OC and EC. The detection limits of OC and EC are 0.2 μg/cm². EC was not detected in the field blanks.

The concentration of total nitrogen (TN) was measured using an elemental analyzer (EA) (Carlo Ebra, EA 1500). A small filter disc with the known area (3.14 cm²) was placed in a tin cup and combusted at 1400 °C in an oxidation column of EA system. All the nitrogen species are converted to NO and then reduced to N₂ in a reduction column. The reduced N₂ was measured with a thermal conductivity detector after the purification using a packed GC column to isolate N₂ from CO₂ [30,31,32]. The analytical error for duplicate analysis is less than 10%. Organic nitrogen (ON) can be calculated using the following equation [32].

where IN means inorganic nitrogen obtained by the summation of nitrogen contents of NH₄⁺ and NO₃⁻ measured by IC. Measurements of OC, TN and major ions were completed in 2009.