Novel insights on new particle formation derived from a pan-european observing system

The formation of new atmospheric particles involves an initial step forming stable clusters less than a nanometre in size (<~1 nm), followed by growth into quasi-stable aerosol particles a few nanometres (~1–10 nm) and larger (>~10 nm). Although at times, the same species can be responsible for both processes, it is thought that more generally each step comprises differing chemical contributors. Here, we present a novel analysis of measurements from a unique multi-station ground-based observing system which reveals new insights into continental-scale patterns associated with new particle formation. Statistical cluster analysis of this unique 2-year multi-station dataset comprising size distribution and chemical composition reveals that across Europe, there are different major seasonal trends depending on geographical location, concomitant with diversity in nucleating species while it seems that the growth phase is dominated by organic aerosol formation. The diversity and seasonality of these events requires an advanced observing system to elucidate the key processes and species driving particle formation, along with detecting continental scale changes in aerosol formation into the future.

Structures of the van der Waals Isomers of Halosulfuric Acids: Microwave Spectra of HX-SO3 (X = F, Cl, Br)

The complexes of SO3 with HF, HCl, and HBr have been studied by microwave spectroscopy. In all three systems, the halogen atom approaches the SO3 on or near its C3 axis, and the vibrationally averaged structure is that of a symmetric top. The S-X bond lengths are 2.655(10), 3.1328(57), and 3.2339(85) Å for the HF, HCl, and HBr complexes, respectively, and in all three systems the out-of-plane distortion of the SO3 is negligible. In HF-SO3, the hydrogen points away from the SO3 and hyperfine structure in the DF complex gives an average angle of 47.7 degrees with respect to the vibrationally averaged C3 axis of the complex. In the HCl and HBr complexes, however, the HX unit is nearly parallel to the SO3 plane. In HCl-SO3, the HCl forms a 72.8 degrees angle with the average C3 axis of the complex, with the proton tilting slightly toward the SO3. In HBr-SO3, the average orientation of the HBr is 73.0 degrees off the symmetry axis of the complex, but the direction of the tilt (toward or away from the SO3) is not determined. Although the hydrogen halides react with SO3 in bulk to produce halosulfuric acids, these gas-phase complexes are much like weakly bound dimers. Copyright 1998 Academic Press.