Atmospheric aerosols often consist of mixtures of inorganic and organic substances. Organic matter contributes to 20-60% of fine particles, depending on location. Knowledge of the water uptake of the organic portion of atmospheric aerosol has been limited. Some researchers have suggested that organics, which most of them are sparingly soluble compounds or surfactants, have a negative effect on the growth factor or evaporation rate of inorganics. However, some researchers have found that organics can both positively and negatively affect the hygroscopicity of inorganic aerosols. Experimental methods used in the literature include: TDMA, electrodynamic balance (EDB), humidgraph (used in this study), single droplet levitation, etc.

Field Study ( ICARTT ) and Preliminary Results (http://www.al.noaa.gov/ICARTT/FieldOperations/FOF.shtml)

Aerosol optical and hygroscopic properties were measured onboard the NOAA RV Ronald H. Brown as part of the ICARTT (International Consortium for Atmospheric Research on Transport and Transformation) in the Gulf of Maine during July and August of 2004. Our results are important to better understand the hygroscopic properties of atmospheric aerosol at ambient humilities and to parameterize ambient aerosol optical properties for use in relative large-scale climate models.

Summary and Conclusions

1. Scattering coefficients

• Ranged from 0 ~ 194 Mm-1

• Comparable to the Polluted and Volcanic air mass during ACE-Asia

2. Curve structures

• Dependent upon air mass type and chemical compositions

• Organic compounds à reduce the hygroscopicity

• Sulfate à more hygroscopic growth and possibility of deliquescence

• Monotonic hygroscopic w/o observable deliquescence or hysteresis 3.Hydration state of ambient aerosols

• Mostly intermediate to upper and lower branches of the hysteresis loop

• Lower/upper branches similar growth (stable h(RH) ~1, l Dependence)