Real-Time Liquid Water Mass Measurement for Airborne Particulates

This note presents a potential approach for the real-time field measurement of the liquid water (LW) content of aerosol particles.With the "inferential" measurement technology presently available, it has been shown that LW is often an important aerosol constituent.This is especially true at elevated values of relative humidity (RH), as hygroscopic compounds deliquesce.Based on light scattering measurements, Rood et al. (1989) concluded that significant quantities of LW are present in a metastable thermodynamic condition at RH as low as 50% to 60%.Nonurban particle measurements utilizing differential mobility sizing indicate that LW may be present in a stable condition at RH values in the 40% to 50% range (e.g., Zhang et al., 1993;Saxena et al., 1995).Models that simulate aerosol chemistry including volatile constituents such as water (e.g., Pilinis et al., 1989;Wexler and Seinfeld, 1991;Kim et al., 1993) are increasingly useful in radiation transfer, visibility, and air quality research; improved LW field data would be helpful in advancing and evaluating such models.Present real-time measurement methods must infer LW mass based on measurements of some other parameter such as particle size or light scattering, leading to the propagation and amplification of uncertainties