Concentrations and Adsorption Isotherms for Amphiphilic Surfactants in PM₁ Aerosols from Different Regions of Europe

Abstract

Predicting the activation of sub-micron particles into cloud droplets in the atmosphere remains a challenge. The importance of surface tension,  (mN/m), in these processes has been evidenced by several works but information on the "surfactants" lowering  for atmospheric particles remains scarce. In this work, PM1 aerosols from urban, coastal and remote regions of Europe (Lyon, France, Rogoznica, Croatia, and Pallas, Finland, respectively) were investigated and found to contain amphiphilic surfactants in concentrations up to 2.8 g m -3 in the air and 1.3 M in the particle volume. In Pallas, correlations with the PM1 chemical composition showed that amphiphilic surfactants were present in the entire range of particle sizes, thus confirming recent works. This implied that they were present in hundreds to thousands particles cm -3 and not only in a few large particles, as it has been hypothesized. Their adsorption isotherms and Critical Micelle Concentration (CMC) were also determined. The low CMC obtained (3  10 -5 -9  10 -3 M) imply that surface tension depression should be significant for all the particles containing these compounds, even at activation (Growth Factor = 10). Amphiphilic surfactants are thus likely to enhance the CCN ability of sub-micron atmospheric particles.

The surface tension of surfactant-containing, finite volume droplets

“…The surface monolayer model predictions suggest surfactant concentrations on the order of several tens to 100 mM, consistent with reported atmospheric concentrations, are required to substantially affect N d (i.e., modify SS c by >20%). These predictions highlight the necessity of a more comprehensive understanding of the types and concentrations of surfactants in aerosol, as to date only a few studies in a few environments have been reported (7,8,10,29,46,47). Global simulations of N d have only rarely incorporated such surface partitioning models (5,6), in part because partitioning effects had not been experimentally confirmed until this work.…”

“…Consequently, the monolayer partitioning model predictions suggest that the total surfactant concentration in particles must be at least on the order of several tens to 100 mM for there to be a substantial effect on cloud droplet activation. Gérard et al (7,29) recently reported total surfactant concentrations in collected ambient fine aerosol reaching several tens to hundreds millimolar across Europe. Moreover, surfactant concentrations are enhanced in smaller (<200-nm diameter) atmospheric particles (46).…”

“…Most approaches infer surface tension from hygroscopic growth or critical supersaturation measurements (28). Moreover, many studies report only macroscopic solution surface tension measurements and do not consider surfacebulk partitioning effects (4,7,8,16,29). Consequently, predictions of surfactant partitioning in aerosol are not accompanied by direct…”

In situ cloud ground-based measurements in the Finnish sub-Arctic: intercomparison of three cloud spectrometer setups

“…However, even when we consider the best agreement, the maximum difference in obtained LWC between CAS and FSSP could still be about 40 %. In addition, we suggest the deployment of another LWC sensor, e.g., the particle volume monitor (PVM-100; Gerber, 1999), during future campaigns in order to obtain another reference LWC value for intercomparison in a wide temperature range. In addition, we are continuously pursuing the development of a new generation of counters designed for ground-based in situ cloud measurements.…”

“…He stated that FSSP can be regarded as an excellent microphysical sensor in continental, stratiform or cumuliform clouds with mostly small drops; however he noticed some discrepancies in the liquid water content, especially when cloud droplets larger than 25 µm were considered. Gerber et al (1999) performed and evaluated ground-based measurements of liquid water content using also an FSSP and a particle volume monitor (PVM). They observed large discrepancies too and stated that the FSSP overestimated liquid water content for large cloud droplets due to the inertial concentration effect.…”