Relative Humidity-Dependent HTDMA Measurements of Ambient Aerosols at the HKUST Supersite in Hong Kong, China

Figures & data

FIG. 1. Average of ((κ_RH – κ_>90)/κ_>90) against RH for the 58 cycles of GF-RH measurements. Note that there is only one data point at 20% RH, hence no standard deviation is available.

FIG. 2. GF as a function of RH for (a) Group 1a: less hygroscopic without hysteresis, (b) Group 1b: less hygroscopic with hysteresis, (c) Group 2: moderately hygroscopic with hysteresis, and (d) Group 3: more hygroscopic with hysteresis of ambient aerosols. Both dehydration (circle [blue] and solid line) and hydration (diamond [red] and dashed line) routes are shown. The lines connect the average GF at each RH.

TABLE 1 Summary of κ_>90, mass, mass fractions of organics, sulfate, nitrate, ammonium, and mole ratio of (NH₄-NO₃)/SO₄

	Without hysteresis*	With hysteresis*
	Less hygroscopic (1a), n = 7	Less hygroscopic (1b), n = 13	Moderately hygroscopic (2), n = 20	More hygroscopic (3), n = 18
κ>90	0.21 ± 0.02	0.24 ± 0.03	0.32 ± 0.03	0.41 ± 0.03
mOrg (μg/m^3)	1.00 ± 0.37	0.62 ± 0.28	0.48 ± 0.30	0.38 ± 0.25
mSO4 (μg/m^3)	0.51 ± 0.24	0.60 ± 0.38	0.66 ± 0.63	0.98 ± 0.72
mNO3 (μg/m^3)	0.24 ± 0.14	0.08 ± 0.05	0.07 ± 0.06	0.04 ± 0.03
mNH4 (μg/m^3)	0.22 ± 0.09	0.24 ± 0.13	0.25 ± 0.21	0.33 ± 0.22
f(Org)	0.51 ± 0.03	0.43 ± 0.11	0.35 ± 0.09	0.23 ± 0.07
f(SO4)	0.25 ± 0.06	0.36 ± 0.09	0.42 ± 0.09	0.56 ± 0.07
f(NO3)	0.12 ± 0.05	0.06 ± 0.04	0.06 ± 0.04	0.02 ± 0.02
f(NH4)	0.11 ± 0.01	0.15 ± 0.04	0.17 ± 0.05	0.20 ± 0.04
n(NH4-NO3)/nSO4	1.73 ± 0.49	2.08 ± 0.61	2.02 ± 0.73	1.84 ± 0.51

*Values in the table are presented as average value ± standard deviation.

FIG. 3. Correlation plots between κ_>90 or κ_f and mass fractions of (a) total organic, (b) sulfate, (c) nitrate, (d) ammonium, and (e) mole ratio of ammonium nitrate to sulfate. Correlation plot between (f) mole ratio of ammonium nitrate to sulfate and total organic mass fraction is also obtained. Dashed lines in each plot are the linear fittings between the two parameters, with an R² at the bottom left corner.

FIG. 4. Closure analysis between κ′ calculated from regression Model III and (a) κ_>90 (triangle [green]) or (b) κ_f (circle [red]). Closure analysis between κ′ calculated using ZSR mixing rule (square [purple]) and κ_>90 is also plotted in (a).

FIG. 5. Example of datasets of which the fitted (dashed line) and predicted GF curves obtained by κ′_>90 (square [blue] and dashed line) or κ′_ZSR (circle [green] and solid line) agree yet deviate from the measured GF-RH trend (circle [red]).

FIG. 6. Measured GF (circle [red]) and predicted GF calculated using κ′_ZSR (circle [green] and solid line) of 17 cycles of which κ′_ZSR and κ_>90 differ by over 20%.

FIG. 7. Performance test of κ′ on (a) seven sets of GF measurements made in January and February 2012, which were not parameterized, and (b) six sets made in August 2012. Predicted GF curves calculated by κ′_>90 (square [blue] and dashed line) obtained from Model III or κ′_ZSR (circle [green] and solid line) is compared with actual measurements made by the HTDMA (circle [red]).