Characterization of an Aerodyne Aerosol Mass Spectrometer (AMS): Intercomparison with Other Aerosol Instruments

Figures & data

TABLE 1 Summary of intercomparison periods

		AMS
Period	Tamb ^a	Tinlet	Tinlet − Tamb ^a	Tinlet–Td ^a	Inlet RH ^a	PILS-IC ^b Size cut	OC ^c Size cut
Phase 1
May 10–12	17° ± 3°C	24°C	7° ± 3°C	17° ± 3°C	34 ± 6%	PM1	N/A ^d
	(11°–21°C)		(3°–13°C)	(13°–23°C)	(21–44%)
Phase 2
July 23–30	23° ± 3°C	35°C	12° ± 3°C	16° ± 2°C	39 ± 5%	PM1	PM1
	(17°–27°C)		(8°–18°C)	(13°–20°C)	(29–48%)
Phase 3
October 1–15	18° ± 3°C	24°, 30°, 32°C	11° ± 4°C	19° ± 3°C	31 ± 7%	PM10	PM1
	(12°–28°C)		(2°–20°C)	(10°–27°C)	(18–53%)

FIG. 1 Schematic diagram of the Aerodyne Aerosol Mass Spectrometer (AMS) and the sampling system for ambient measurements.

FIG. 2 Time series of (a) the air beam (AB) signal and (b) the ratio of the ionization efficiency for nitrate (IE _{NO 3} ) to the AB signal. The AB data are 12-h averages. The solid line and dashed line in Figure 2b indicate the average and 2σ variability range of the IE _{NO 3} /AB ratios, respectively.

FIG. 3 Time series of the background signal at m/z = 30 (NO⁺) in the AMS mass spectra and nitrate mass loadings in ambient air. The data are 12-h averages.

TABLE 2 Limits of Detection (LODs) for AMS measurements (1-h average)

		LOD (Filter) ^b , μ g m^− 3
Species	LOD (Ion counting) ^a , μ g m^− 3	Best estimate	95% confidence interval
Nitrate	0.01	0.02	0.01–0.04
Sulfate	0.03	0.01	0.008–0.03
Chloride	0.01	0.02	0.01–0.04
Ammonium	0.1	0.2	0.1–0.4
Organics	0.1	0.3	0.2–0.6
Water	1	0.5	0.3–1

FIG. 4 Scatter plot of measured and predicted NH₄ ⁺ derived from the PM₁ PILS-IC measurements in May (open circles) and July (solid circles) 2003. The data are 1-h averages. The predicted NH₄ ⁺ was determined assuming that measured anions (SO₄ ^{2 −}, NO₃ ⁻, and nss-Cl⁻) were fully neutralized by NH₄ ⁺. The dot-dashed line indicates 1:1 correspondence line.

FIG. 5 Scatter plots of AMS versus PM₁ PILS measurements in May (open circles) and July (solid circles) 2003. The data are 1-h averages. The dashed and solid lines represent the linear regression lines for May and July 2003, respectively. Note that CE = 0.5 is assumed for all of the AMS inorganic species. The dot-dashed line indicates 1:1 correspondence line.

TABLE 3 Summary of intercomparison results

	Fit parameters ^a
Species	Slope	Intercept, μ g m^− 3	r^2
		Phase 1 (May 10–12, 2003)
Nitrate	1.12 ± 0.03	0.33 ± 0.09	0.99
Sulfate	1.24 ± 0.11	−0.34 ± 0.32	0.85
Chloride	1.16 ± 0.05	0.10 ± 0.03	0.96
Ammonium	1.26 ± 0.06	−0.38 ± 0.15	0.96
		Phase 2 (July 23–30, 2003)
Nitrate	0.81 ± 0.03	0.46 ± 0.18	0.95
Sulfate	0.90 ± 0.06	0.44 ± 0.18	0.88
Chloride	0.91 ± 0.05	0.07 ± 0.02	0.92
Ammonium	0.95 ± 0.06	0.25 ± 0.17	0.89
Organics	1.79 ± 0.29	0.98 ± 0.84	0.67
		Phase 3 (October 1–15, 2003)
Organics	1.61 ± 0.09	0.86 ± 0.52	0.83

FIG. 6 Monthly average size distribution of nitrate (solid line), sulfate (dashed line), and organics (shaded line) for July 2003.

FIG. 7 Scatter plots of AMS organics (OM_AMS) and OC mass concentrations in July and October 2003. The data are 1-h averages. The shaded line represents the linear regression line. The dashed lines indicate 1:1 and 2:1 correspondence lines.

FIG. 8 OM_AMS/OC ratios as a function of m/z 44/OM_AMS ratio. The data are 1-h averages. The open squares and bars represent the average values and standard deviations for each m/z 44/OM_AMS ratio bin, respectively.