ABSTRACT
New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid-ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models.
ABSTRACT
Two extraction procedures for ecologically relevant elements present in automotive brake linings (Sb, Bi, Pb, Cd, Cr (total), Co, Cu, Mo, Ni, Sr, V, Zn, Sn) were developed and validated, applying a high pressure asher (HPA-S) and microwave extraction, respectively. Both of these methods allowed for the quantitative analysis of the extracted elements by inductively coupled plasma optical emission spectrometry (ICP-OES). The results were compared to measurements using a handheld energy-dispersive X-ray fluorescence spectrometer (ED-XRF), being in discussion by regulating agencies as in-situ screening tool for brake pads. The comparison indicates that the handheld ED-XRF analysis is basically an efficient screening tool for a reliable assessment of trace metal contents in automotive brake pads with respect to legal standards. While a quantitative determination of elements like Cd, Co, Cr, Mn, Mo, Ni, Pb and Sb was achievable, other elements (V, Cu, Bi, Zn, Sn and Sr) could only be determined qualitatively due to the special matrix characteristics of brake pads.
