A study on effects of size and structure on hygroscopicity 

of nanoparticles using a tandem differential mobility 

analyzer and TEM 

Kihong Park Æ Jae-Seok Kim Æ 

K. Park J.-S. Kim
 

Research Center for Biomolecular Nanotechnology,
 

Department of Environmental Science and Engineering,
 

Gwangju Institute of Science and Technology (GIST),
 

261 Cheomdan-gwagiro (Oryong-dong), Buk-gu,
 

Gwangju 500-712, Republic of Korea
 

e-mail: kpark@gist.ac.kr
 

Arthur L. Miller 

A. L. Miller 

National Institute for Occupational Safety and Health/ 

Spokane Research Lab, Spokane, WA 99207, USA 

Abstract A hygroscopicity tandem differential 

mobility analyzer (HTDMA) technique is used to 

determine size-effect of nanoparticles (NaCl, (NH4)2 

SO4, KCl, NH4NO3, MgCl2, CaCl2) on their hygroscopic properties (deliquescence relative humidity 

(DRH) and hygroscopic growth factor (GF)). The 

HTDMA system uses a combination of two nano 

DMAs and two regular DMAs to measure particle size 

change in a wide dynamic particle size range. Particles 

are subsequently analyzed with a transmission electron 

microscopy to investigate the potential effect of 

particle structure or morphology on the hygroscopic 

properties. We found that structural properties of NaCl 

and (NH4)2SO4 particles also play an important role in 

determination of the DRH and GF and are more 

pronounced at smaller diameters. Data show that the 

DRH of NaCl nanoparticles increased from *75% up 

to *83% RH at 8 nm and that their GF decreased with 

decreasing size. The extent to which the GF of NaCl 

nanoparticles decreased with decreasing size was 

greater than theoretically predicted with the Kelvin 

correction. The GF of furnace-generated NaCl nanoparticles that have pores and aggregate shape was 

found to be smaller than that of atomizer-generated 

particles that are close to perfectly cubic. For the case 

of atomizer-generated (NH4)2SO4 nanoparticles, we 

observed no significant size-effect on their DRH, and 

the measured GF agreed well with predicted values 

using the Kelvin correction. For furnace-generated 

(NH4)2SO4 nanoparticles, a gradual growth at moderate RH without noticeable deliquescence behavior 

occurred. Their TEM images showed that contrary to 

atomizer-generated (NH4)2SO4 nanoparticles the furnace-generated (NH4)2SO4 nanoparticles are not 

perfectly spherical and are often aggregates having 

pores and holes, which may favor holding residual 

water even in the dried condition. For atomizergenerated KCl, MgCl2, and CaCl2 nanoparticles, we 

observed no significant size-effects on their DRH and 

GF for the mobility size as small as 20 nm. 

Introduction 

Fine and ultrafine particles in the ambient atmosphere 

are of current interest due to their effects on the 
radiation budget (Intergovernmental Panel on Climate Change 2007), climate change, visibility, and 

human health. Especially, ultrafine particles and 

nanoparticles may have higher reactivity and toxicity 

due to their enhanced surface area-to-volume ratio 

(Peters et al. 1997; Oberdo ̈rster 2000). Those particles in the ambient atmosphere are emitted directly 

from various sources or formed by gas-to-particle 

conversion process. The new particles formed can 

grow to sizes that are optically important and have a 

potential to affect climate change. Due to their small 

size and mass, the newly formed particles are easily 

lost by diffusion and it is difficult to determine their 

chemical composition. Thus, rapid measurements of 

physical and chemical properties of nanoparticles are 

essential to better understand their sources, particle 

formation and growth mechanisms, and their effects 

on atmospheric processes and human health. 

The development of the aerosol mass spectrometry 

technique made it possible to directly determine 

chemical composition of submicron particles in real 

time, but the detectable size is limited to 50–200 nm 

depending on the type of aerosol mass spectrometry 

(Suess and Prather 1999; Noble and Prather 2000; 

Nash et al. 2006). Recently, by measuring the hygroscopicity of nanoparticles, the composition of the 

newly formed particles was estimated (Sakurai et al. 

2003; Sakurai et al. 2005). This can be done by 

comparing hygroscopic properties of the freshly 

formed nanoparticles in the ambient atmosphere with 

those of standard particles of known hygroscopicity. 

Hygroscopic properties are key properties of aerosol 

particles, affecting particle growth by water vapor, 

scattering efficiency of particles, and potential for the 

formation of cloud condensation nuclei. Also, an 

accurate measurement of hygroscopic properties of 

nanoparticles is essential for better understanding of 

atmospheric nanoparticle formation and growth. 

However, there has been limited information on how 

the hygroscopic properties of atmospheric particles 

will vary with decreasing size below 50 nm. Hygroscopic properties (deliquescence relative humidity 

(DRH) and growth factor (GF)) of nanoparticles may 

or may not be the same as those of submicron or larger 

particles. For example, theoretical prediction of the 

GF using the Kelvin correction would not suffice to 

accurately determine hygroscopic behaviors for such 

small particles (Ha ̈meri et al. 2000; Ha ̈meri et al. 

2001; Russell and Ming 2002). 

Thus, this study focuses on how hygroscopic 

properties (DRH and GF) of nanoparticles vary with 

their size and structural properties. We combined a 

hygroscopicity tandem differential mobility analyzer 

(HTDMA) technique with transmission electron 

microscopy to measure the hygroscopic properties 

of various size-resolved nanoparticles such as NaCl, 

(NH4)2SO4, KCl, NH4NO3, MgCl2, and CaCl2, which 

might be possible candidates for constituents of 

hygroscopic nanoparticles in the ambient atmosphere, 

and to investigate the potential effect of particle 

structure or morphology on the hygroscopic properties. Two different particle generation methods 

(atomizer versus furnace reactor) were used in this 

study. A combination of nano DMAs and regular 

DMAs was made to measure particle size change in a 

wide dynamic particle size range in our HTDMA 

system. 

Experimental 

The hygroscopicity tandem differential mobility 

analyzer (HTDMA) mainly consists of two regular 

Differential Mobility Analyzers (DMA, TSI 3081) 

(Knutson and Whitby 1975), two nano Differential 

Mobility Analyzers (nano DMA, TSI 3085) (Chen 

et al. 1998), an Ultrafine Condensation Particle 

Counter (UCPC, TSI 3776), and a humidification 

system, as shown in Fig. 1. The tandem measurement 

methods used have been described previously (Radar 

and McMurry 1986; McMurry and Stolzenburg 1989; 

McMurry et al. 2002; Park et al. 2003). For our 

research, test aerosols were generated by using an 

atomizer (TSI 3076) and a furnace reactor. Particles 

were first dried to about *7% RH using a Nafion 

drier or a diffusion drier, and passed through a 210Po 

‘‘neutralizer’’ and then selected according to mobility 

size with the first nano or regular DMA. The accuracy 

of all DMAs was tested using the standard PSL 

particles. The selected particles of a certain size 

(3–200 nm) were then sent into a humidifier (7–90% 

RH) and subsequently routed to the second nano or 

regular DMA and UCPC system to determine particle 

size change under the elevated relative humidity. The 

particle size change as a function of RH was used to 

determine the DRH (i.e., relative humidity at which 

sudden condensation-driven growth occurs), if exist, 

and growth factor (the ratio of particle mobility 
diameter at increased RH to that at dry condition). 

When particles grew to a larger size than the upper 

size limit (*80 nm) of the nano-DMA, the second 

regular DMA was used to measure particle growth. In 

this way, we are able to determine size-resolved 

hygroscopic growth of nanoparticles in a wide size 

range. Relative humidity was measured by capacitance sensors (Omega HX94AV and GE sensing 

MMR31) with an accuracy of ±2.5% and ±2% RH. 

Fig. 1 A schematic of the 

hygroscopicity tandem 

differential mobility 

analyzer (HTDMA) system 

Six types of nanoparticles were chosen for this 

study (i.e., NaCl, (NH4)2SO4, KCl, NH4NO3, MgCl2, 

and CaCl2 particles). These were chosen because they 

might be considered as possible candidate species for 

hygroscopic ultrafine particles and nanoparticles in 

the ambient atmosphere. Particles larger than 30 nm 

were produced from 0.1% (wt) DI water solution 

using an atomizer (TSI 3076). To produce particles 

smaller than *30 nm, a furnace reactor system 
employing an evaporation-condensation method was 

used. In this method, a quartz boat was placed in the 

center of the furnace reactor containing 300 mg of 

sample material and the filtered air was used as a 

carrier gas. The furnace temperature is set below the 

melting temperature of the sample (e.g., 200 °C for 

(NH4)2SO4). The material evaporates and subsequently cools quickly upon exiting the furnace 

causing homogeneous nucleation of nanoparticles. 

To obtain size distribution of laboratory-generated 

particles, we used the scanning mobility particle sizer 

(SMPS) (DMA: TSI 3081, CPC: TSI 3022A). 

Morphology of the nanoparticles was examined by 

using a transmission electron microscope (JEOL 

JEM-2100). 

Results and discussion 

Table 1 summarizes material properties (density, 

solubility, surface tension, melting point, boiling 

point, and theoretical DRH) of the six types of 

particles tested in this study. 

Table 1 Material properties of particles tested in this study 

DRHa,b 

(g/mol) (g/cm3) (g/100 g H2O) (N/m) at 90% RH pointa (

o

C) pointa (°C) (%) 

Name Formula weighta Densitya Solubilitya Surface tension Melting Boiling 

NH4NO3 80.04 1.72 213 170 210 61.8 

(NH4)2SO4 132.14 1.77 76 0.082 235–280 N/A 79.9 ± 0.5 

CaCl2 110.99 2.15 81 772 [1,600 29.0 

MgCl2 95.23 2.32 56 712 1,412 33.0 

KCl 74.56 1.99 36 790 1,500 84.2 ± 0.3 

NaCl 58.45 2.17 36 0.077 800 1,413 75.3 ± 0.1 

a CRC Handbook (2003)

b Seinfeld and Pandis (1998)

During tests, we 

determined the actual DRH of those nanoparticles 

by measuring particle GF as a function of relative 

humidity with the HTDMA technique. Figure 2 

shows the GF of NaCl nanoparticles as a function 

of RH. 

Fig. 2 GF of NaCl nanoparticles as a function of RH 

including theoretically predicted GF with Kelvin correction 

(based on calculation by Ha ̈meri et al. 2001)

The NaCl nanoparticles were produced by 

both an atomizer and a furnace reactor described in 

the experimental section. The theoretically predicted 

GF for 8 and 100 nm particles with the Kelvin 

correction based on calculation by Ha ̈meri et al. 

(2001) was also included in Fig. 2. As shown, the size 

of the 100 nm mobility diameter NaCl particles 

increases abruptly from 100 to 182 nm yielding a GF 

of 1.82 at *76% RH, which is close to the theoretical 

DRH value (75.3% RH) (see Table 1). The 30, 50, 

and 80 nm NaCl particles were determined to have 

the same deliquescence behavior as that of the 

100 nm particles. However, for particles smaller than 

20 nm, we found that the DRH of NaCl particles 

increased and reached up to *83% RH for 8 nm 

NaCl particles. This confirms the conclusions of 

Biskos et al. (2006a, b), who reported that due to 

lower surface free energy of the crystalline particles 

than aqueous particles, the crystalline state is favored, 

leading to the increase of the DRH. This condition 

can be described as when the surface tension ratio of 

the crystalline particles to the aqueous particles is 

smaller than the diameter ratio of the crystalline 

particles to the aqueous particles (Biskos et al. 

2006a). This suggests that surface property plays an 

important role in the determination of the DRH and is 

more pronounced at smaller diameters. 
For the case of 20 nm NaCl nanoparticles, we 

observed that the DRH of the atomizer-generated 

particles increased to *81%, while the DRH of the 

furnace-generated particles had no increase (i.e., 

DRH = *75%). This is not surprising since the 

surface properties of the furnace-generated NaCl 

nanoparticles would differ from that of the atomizergenerated NaCl nanoparticles. Our results suggest 

that the surface tension ratio of the crystalline 

particles to the aqueous particles would be smaller 

for the atomizer-generated NaCl particles than the 

furnace-generated NaCl particles. In other words, the 

surface free energy of the atomizer-generated NaCl 

particles is smaller than the furnace-generated NaCl 

particles. Relatively higher porosity of the furnacegenerated NaCl particles may lead to the higher 

surface free energy, as will be shown in TEM images 

later in this section. Regardless of the generation 

method, we did not observe any particle shrinkage or 

growth with increasing RH at moderate RH below the 

DRH, suggesting that the NaCl particles did not 

experience any significant restructuring or water 

adsorption below the DRH. Figure 3 compares the 

size-dependent DRH of NaCl nanoparticles as a 

function of particle mobility diameter with previous 

data. Fig. 3 Size-dependent DRH of NaCl nanoparticles as a 

function of particle mobility diameter including previous NaCl 

data (Ha ̈meri et al. 2001; Biskos et al. 2006a) 

It shows that the current size-dependent DRH is 

qualitatively consistent with the previous measurements (Ha ̈meri et al. 2001; Biskos et al. 2006a) and 

that the amount of increase varies with the generation 

method for particles smaller than 40 nm. 

Figure 4 summarizes average hygroscopic GFs of 

the sodium chloride nanoparticles at 80% RH, 85% 

RH, and 90% RH using all measured data. 

Fig. 4 Hygroscopic growth 

factors of NaCl 

nanoparticles averaged at 

80% RH, 85% RH, and 

90% RH and theoretical 

values with Kelvin 

correction at 90% RH 

(particles smaller than 

20 nm was generated by 

furnace while particles 

larger than 20 nm were 

generated by an atomizer) 

Data 

clearly showed that growth factor of the sodium 

chloride nanoparticles decreased as the mobility size 

decreases. The mobility diameter growth factor at 

*80% RH is 1.50 for 10 nm particles compared to 

1.89 for 100 nm particles. This can be explained by 

the enhanced water vapor pressure for nanoparticles 

due to the Kelvin effect. The theoretical prediction 

for GF accounting for the Kelvin effect was included 

in Fig. 4. There is still *17% difference for 8 nm 
particles at 90% RH between the measured GF and 

the theoretically predicted value with the Kelvin 

correction. The difference decreased as particle size 

increased above 50 nm. This suggests that in addition 

to the Kelvin effect, the size-dependent density and 

shape of NaCl nanoparticles, which differ from the 

bulk material density and spherical shape used for 

calculating the theoretical GF, may play a role in the 

observed difference. Note that theoretical thermodynamic prediction for the GF is based on the 

assumption that the particle is perfectly spherical 

and the solute density is 2.165 g/cm3 (Lide 2003). 

Fig. 5 TEM images for (a) 

furnace-generated NaCl 

nanoparticles and (b) 

atomizer-generated NaCl 

particles 

Accounting for particle shape using the dynamic 

shape factor of NaCl, which is known to be 1.08 

(Hinds 1999; Biskos et al. 2006b), was not enough to 

explain the observed difference. We also observed 

that the GF of the furnace-generated NaCl 

nanoparticles is smaller than that of atomizer-generated particles having the same size. If the solute 

density is smaller than the bulk material density, the 

GF will decrease (Ha ̈meri et al. 2000; Ha ̈meri et al. 

2001). It is not certain that the dry salt density of the 

furnace-generated NaCl nanoparticles is smaller than 

that of atomizer-generated particles. Voids formed by 

imperfect crystal growth and trapped water may 

affect the solute density of the NaCl particles (Weis 

and Ewing 1999). As shown in Fig. 5a, TEM images 

for the furnace-generated NaCl nanoparticles showed 

that they are not perfectly cubic but have somewhat 

rounded corners and that they have pores and are 

sometimes aggregates. On the contrary, the atomizergenerated NaCl nanoparticles are perfectly cubic as 

shown in Fig. 5b. It is possible that the pores and 

aggregate shape contribute to the smaller density of 
the furnace-generated NaCl nanoparticles, leading to 

the smaller GF of the furnace-generated NaCl 

nanoparticles than that of atomizer-generated particles. Also, particles with pores or voids can trap 

water leading to lower density. 

Fig. 6 (a) GF as a function of RH for atomizer-generated 

(NH4)2SO4 nanoparticles including theoretically predicted GF 

based on calculation by Biskos et al. (2006c) and (b) GF as a 

function of RH for furnace-generated (NH4)2SO4 nanoparticles 

including theoretically predicted GF based on calculation by 

Biskos et al. (2006c) 

Figure 6a shows the measured GF as a function of 

RH for atomizer-generated (NH4)2SO4 nanoparticles 

and included the theoretically predicted GF based on 

calculation by Biskos et al. (2006c). The DRH of 

(NH4)2SO4 nanoparticles is around 79%, which 

agrees well with the theoretical value (79.9% RH) 

(i.e., there is no size-effect on the DRH of (NH4)2SO4 

nanoparticles contrary to NaCl nanoparticles). Also, 

the measured GFs agreed with the predicted values 

for atomizer-generated (NH4)2SO4 nanoparticles 

within 10%. This suggests that the solute density 

and structure of (NH4)2SO4 nanoparticles are not 

much dependent on size compared to NaCl 

nanoparticles. Figure 6b shows the GF as a function 

of RH for furnace-generated (NH4)2SO4 nanoparticles in the size range of 8–30 nm. These (NH4)2SO4 

nanoparticles showed no significant deliquescence 

behavior. There is a gradual growth starting at 

50–60% RH below the theoretical DRH value 

of (NH4)2SO4 particles (Tang 1980; Tang and 

Munkelwitz 1993). Water adsorption on to surface 

of (NH4)2SO4 particles at moderate RH can lead to 

the gradual growth without deliquescence behavior. 

Fig. 7 TEM images for (a) furnace-generated (NH4)2SO4 

particles and (b) atomizer-generated (NH4)2SO4 particles 

This occurred only for furnace-generated (NH4)2SO4 
nanoparticles, which suggests that possibly these 

nanoparticles may trap water (i.e., not dried out 

perfectly), causing water adsorption at moderate RH. 

As shown in Fig. 7, TEM images showed that 

contrary to atomizer-generated (NH4)2SO4 nanoparticles, the furnace-generated particles are not 

perfectly spherical and are sometime aggregates 

having pores and holes, which may favor holding 

residual water even in dried condition. Thus, we 

argue that hygroscopic growth of the freshly formed 

ammonium sulfate nanoparticles in the ambient 

atmosphere may depend on not only composition 

but also their structure/shape properties. 

Figure 8 shows the hygroscopic GFs for KCl, 

MgCl2, CaCl2, and NH4NO3 nanoparticles. The 

dotted line represents the DRH of bulk materials as 

included in Table 1. For KCl, MgCl2, and CaCl2 

nanoparticles, we observe no significant size-effects 

on their DRH and GF, while for NH4NO3 nanoparticles we observe a size-dependent GF (smaller GF 

for smaller particles) in the size range of 20–100 nm. 

Also, NH4NO3 nanoparticles have no abrupt 

deliquescence behavior and a gradual growth below 

the theoretical DRH (61.8% RH). More research is 

required to determine what makes different deliquescence behaviors for NH4NO3 nanoparticles. 

Fig. 8 Hygroscopic GF for (a) KCl, (b) MgCl2, (c) CaCl2, and (d) NH4NO3 nanoparticles generated by an atomizer (the dotted line 

represents the DRH of bulk materials) 

Conclusion 

By using a HTDMA technique, we examined sizeeffect of six-types of nanoparticles (NaCl, (NH4)2SO4, 

KCl, NH4NO3, MgCl2, CaCl2) on their hygroscopic 

properties. Our data suggest that structure properties of 

NaCl and (NH4)2SO4 nanoparticles affect the DRH and 

GF. NaCl nanoparticles were shown to have an 

increased DRH (83% RH at 8 nm) and their GFs 

below *50 nm were smaller than theoretically predicted values using the Kelvin correction. The GF of 

the furnace-generated NaCl nanoparticles that have 

pores and aggregate shape was found to be smaller than 

that of atomizer-generated particles that are perfectly 

cubic. For the case of atomizer-generated (NH4)2SO4 

nanoparticles, the measured DRH and GF values 
agreed well with those found in the literature value. 

However, for furnace-generated (NH4)2SO4 nanoparticles, we observed a gradual growth at moderate RH 

without deliquescence behavior. TEM images indicated that the furnace-generated (NH4)2SO4 

nanoparticles are not perfect spheres and are sometime 

aggregates having pores and holes, which may favor 

holding residual water even in the dried condition. No 

significant size-dependent hygroscopic behaviors 

occurred for KCl, MgCl2, and CaCl2 nanoparticles 

for the mobility size as small as 20 nm. Our results 

suggest that when hygroscopic data of atmospheric 

nanoparticles are investigated, the specific size-dependent hygroscopic behaviors for different types of 

nanoparticles must be accounted for and that structural 

properties of nanoparticles should be determined for 

certain types of nanoparticles. 

Acknowledgments The research described in this article was 

supported by Eco Science-Technology Advancement Research 

Project. It was partially supported by Korea Research 

Foundation Grant (KRF-2007-331-D00222) and Korea 

Science and Engineering Foundation (KOSEF) (No. R01­

2007-000-10391-0). 

References 

Biskos G, Malinowski A, Russell LM, Buseck PR, Martin ST 

(2006a) Nanosize effect on the deliquescence and the 

efflorescence of sodium chloride particles. Aerosol Sci 

Technol 40:97–106. doi:10.1080/02786820500484396 

Biskos G, Russell LM, Buseck PR, Martin ST (2006b) Nanosize effect on the hygroscopic growth factor of aerosol 

particles. Geophys Res Lett 33:L07801 

Biskos G, Paulsen D, Russell LM et al (2006c) Prompt deliquescence and efflorescence of aerosol nanoparticles. 

Atmos Chem Phys 6:4633–4642 

Chen D-R, Pui DYH, Hummes D, Fissan H, Quant FR, Sem GJ 

(1998) Design and evaluation of a nanometer aerosol 

differential mobility analyzer (Nano-DMA). J Aerosol Sci 

29(5):497–509. doi:10.1016/S0021-8502(97)10018-0

Ha ̈meri K, Vakeva M, Hansson HC, Laaksonen A (2000) 

Hygroscopic growth of ultrafine ammonium sulphate 

aerosol measured using an ultrafine tandem differential 

mobility analyzer. J Geophys Res 105:22231–22242. doi: 

10.1029/2000JD900220 

Ha ̈meri K, Laaksonen A, Vakeva M, Suni T (2001) Hygroscopic growth of ultrafine sodium chloride particles. 

J Geophys Res-Atmos 106:20749–20757. doi:10.1029/ 

2000JD000200 

Hinds WC (1999) Aerosol technology. Wiley-Interscience, 

New York 

Intergovernmental Panel on Climate Change (2007) Climate 

change 2007. Cambridge University Press, New York 

Knutson EO, Whitby KT (1975) Aerosol classification by 

electric mobility: apparatus, theory, and applications. 

J Aerosol Sci 6:443–451. doi:10.1016/0021-8502(75) 

90060-9 

Lide DR (2003) CRC handbook of chemistry and physics, 84th 

edn. CRC Press, London 

McMurry PH, Stolzenburg MR (1989) On the sensitivity of 

particle size to relative humidity for Los Angeles aerosols. 

Atmos Environ 23:497–507. doi:10.1016/0004-6981(89) 

90593-3 

McMurry PH, Wang X, Park K, Ehara K (2002) The relationship between mass and mobility for atmospheric 

particles: a new technique for measuring particle density. 

Aerosol Sci Technol 36:227–238. doi:10.1080/02786820 

2753504083

Nash DG, Baer T, Johnston MV (2006) Aerosol mass spectrometry: an introductory review. Int J Mass Spectrom 

258:2–12. doi:10.1016/j.ijms.2006.09.017 

Noble CA, Prather KA (2000) Real-time single particle mass 

spectrometry: a historical review of a quarter century of 

the chemical analysis of aerosols. Mass Spectrom Rev 

198:248–274. doi:10.1002/1098-2787(200007)19:4\248:: 

AID-MAS3[3.0.CO;2-I 

Oberdo ̈rster G (2000) Toxicology of ultrafine particles: in vivo 

studies. Philos Trans Math Phys Eng Sci 358:2719–2739 

Park K, Cao F, Kittelson DB, McMurry PH (2003) Relationship between particle mass and mobility for diesel exhaust 

particles. Environ Sci Technol 37:577–583. doi:10.1021/ 

es025960v

Peters A, Wichmann HE, Tuch R, Heinrich J, Heyder J (1997) 

Respiratory effects are associated with the number of ultrafine particles. Am J Respir Crit Care Med 155:1367–1383 

Radar DJ, McMurry PH (1986) Application of the tandem 

differential mobility analyzer to studies of droplet growth 

or evaporation. J Aerosol Sci 17:771–787. doi:10.1016/ 

0021-8502(86)90031-5 

Russell LM, Ming Y (2002) Deliquescence of small particles. 

J Chem Phys 116:311–321. doi:10.1063/1.1420727 

Sakurai H, Tobias HJ, Park K, Zarling D, Docherty S, Kittelson 

DB et al (2003) On-line measurements of diesel nanoparticle composition and volatility. Atmos Environ 

37:1199–1210. doi:10.1016/S1352-2310(02)01017-8 

Sakurai H, Fink MA, McMurry PH, Mauldin L, Moore KF, 

Smith JN et al (2005) Hygroscopicity and volatility of 4–10 

nm particles during summertime atmospheric nucleation 

events in urban Atlanta. J Geophys Res 110:D22S04. doi: 

10.1029/2005JD005918 

Seinfeld JH, Pandis SN (1998) Atmospheric chemistry and 

physics. Wiley-Interscience, New Jersey 

Suess DT, Prather KA (1999) Mass spectrometry of aerosols. 

Chem Rev 99:3007–3025. doi:10.1021/cr980138o 

Tang IN (1980) On the equilibrium partial pressures of nitric 

acid and ammonia in the atmosphere. Atmos Environ 

14:819–828. doi:10.1016/0004-6981(80)90138-9 

Tang IN, Munkelwitz HR (1993) Composition and temperature 

dependence of the deliquescence properties of hygroscopic aerosols. Atmos Environ 27:467–473 

Weis DD, Ewing GE (1999) Water content and morphology of 

sodium chloride aerosol particles. J Geophys Res-Atmos 

104:21275–21285. doi:10.1029/1999JD900286