Atmospheric surfactants Chemistry: imProving the predictions of cloUd Formation and Features (CHEMPUFF)

As we know surface tension plays a significant role in the activation process (particles to the droplet growth). Most of the work considered the surface tension of water 72.8 mN/m in Kohler equation, which is not the actual surface tension of deliquesced multicomponent particles/CCN in the atmosphere, in this way questionable.
In Earth's atmosphere, cloud droplets are formed solely by the condensation of water onto aerosol particles suspended in the atmosphere, but these processes are still not well implicit. The Kohler equation is unanimously applied to explain these processes and envisages that surfactants or, surface-reducing compounds, in fine (sub-micron) particles should augment their transformation into a cloud droplet, thus act an important role in cloud droplet numbers and other cloud properties in the atmosphere. Yet for decades this role has been strongly challenged. One difficulty in this debate was for a long time the lack of information on the surfactants present in atmospheric aerosols and their properties.

Amphiphilic surfactants were detected in all the samples analyzed thus indicating their presence in submicrometer particles in an urban and coastal site of Europe. The concentrations were between (0.010 ± 0.003) and (2.8 ± 0.9) μg m−3 in the air assuming a molecular weight of 500 g mol−1 for these compounds, which is typical for amphiphilic molecules: for instance, the molecular weights of SDS, Triton X-114, and rhamnolipids are 288, 537, and between 300 to 600 gmol−1, respectively. The molar concentrations in the particle volume were between (7.2 ± 2.4) mM and (1.3 ± 0.4) M. The lowest concentrations were recorded in Rogoznica (median: 0.08 μg m−3 or 22 mM) and the largest at the urban site of Lyon (median: 0.6 μg m−3 or 73 mM). The concentrations obtained at the coastal site of Rogoznica, Croatia, were consistent with those of amphiphilic surfactants measured at another coastal site previously by our group, in spite of the different sampling resolutions: PM2.5 aerosols from Askö, Sweden (median: 0.1 μg m−3 or 38 mM). Potential correlations between the different ionic fractions of the surfactants, anionic, cationic, and nonionic ones, that would indicate common sources, were investigated. In all the samples the anionic and nonionic fractions largely dominated over cationic ones, the latter being detected only in a few samples and at very small concentrations.

In addition to surfactants analysis, all the samples were analyzed for;
• Total carbon (TC) and nitrogen (TN) and their stable isotopic (δ13C and δ15N) composition,
• Dicarboxylic acids/related compounds and Fatty acids/fatty alcohols,
• Organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and
• Inorganic ion composition
with EA-IRMS, GC/GC-MS, GC-IRMS, EC/OC Analyzer, and TOC Analyzer and IC, respectively.
Relative contribution total carbon (TC) and nitrogen (TN) and their stable isotopic (δ13C and δ15N) composition, carbonaceous aerosol (EC-OC-WSOC), WSTN, dicarboxylic acids and fatty acids of PM1 aerosol sampled during summer 2019 from an urban site (Lyon) of Europe.
24 hrs PM1 sampling was carried out in the summer season at an urban site, Lyon, France. 25 samples were chosen randomly for the detailed analysis of major organic, inorganic and carbonaceous species.
TC and TN Concentration of TC and TN ranged from 1.48 µg m-3 to 5.23 µg m-3 (av. 3.29 µg m-3) and 0.29 µg m-3 to 1.1 µg m-3 (av. 0.58 µg m-3), respectively. Their stable isotopic ratios (δ13C and δ15N) ranged from -28.04 ‰ to -26.48 ‰ (av. -27.15‰) and 13.71 ‰ to 22.08 ‰ (av. 18.21‰), respectively. The relative contribution of TC and TN was 85% and 15%.
Dicarboxylic acids Total dicarboxylic acids (C2-C12) ranged from 0.4-73 ng m-3 (av. 12.4 ng m-3) in PM1 aerosols. Relative abundances of oxalic acid (C2) in total diacids in the Lyon aerosols ranged from 31 to 70% with an average of 53% followed by succinic (C4) acid (av. 17%) and malonic (C3) acid (av. 11%) of total saturated normal chain dicarboxylic acids. The predominance of oxalic acid is reasonable because this diacid is the final product of the photooxidation reaction of several VOCs and unsaturated fatty acids in the atmosphere (Legrand et al. 2007). Oxalic acid may also be emitted directly to some extent from combustion sources such as fossil fuel combustion and biomass burning (Kawamura and Yasui 2005), nevertheless, secondary production of C2 diacid may be more significant in the atmosphere than primary emission (Huang and Yu 2007).
Concentrations of normal diacids generally decreased with an increase in carbon chain length, except for C9 acids. Azealic (C9) acid showed the sixth most abundant diacid (av. 4%). Glyoxylic (ωC2) acid was the most abundant ketoacid, which comprised on average 21% of total ketoacids, followed by ωC4 (av. 18%) and ωC3 (17%). Pyruvic acid was detected in all samples with average concentration 1.88 ng m-3. The concentration of methylglyoxal (av. 1.0 ng m-3) was twice the glyoxal (0.51) ng m-3 in all samples.
Carbonaceous PM1 and surfactants Organic carbon (OC), elemental carbon (EC) and water soluble organic carbon (WSOC) ranged from 1.23µg m-3 to 4.89 µg m-3 (av. 2.83 µg m-3), 0.15 µg m-3 to 1.71 µg m-3 (av. 0.70 µg m-3) and 0.73 µg m-3 to 3.35 µg m-3 (av. 1.85 µg m-3), respectively. In addition to carbonaceous aerosol, water soluble total nitrogen (WSTN) was also detected for understanding the total soluble nitrogen in the PM1, which can be the component of cationic surfactants as nitrogen is the part of cationic surfactants. The WSTN ranged from 0.24 µg m-3 to 1.03 µg m-3 (av. 0.52 µg m-3).

Periodic Reporting for period 1 - CHEMPUFF (Atmospheric surfactants Chemistry: imProving the predictions of cloUd Formation and Features (CHEMPUFF))

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