Time series of nanoparticle number concentration during new particle formation (NPF) events in the urban environment of Brisbane, Australia, showed that the formation of charged particles often occurred before that of neutral particles. We monitored 241 days during the calendar year 2012 over which NPF events were observed on 108 days. We studied the times at which the charged and neutral particle concentrations in the size range 1.8–3.2 nm reached their peak values and found that they were clearly different in 50 events with the peak neutral particle concentration lagging behind the charged particle concentration during 42 of these events with a mean time lag of 24±12 min. While the charged particles were more likely to form before the neutral particles, once formed, the growth rate of the particles did not depend on their charge. While ion-induced nucleation is not the dominant mechanism of NPF in the atmosphere, our observations suggest that the presence of ions in the atmosphere plays a role that cannot be ignored.
PM2.5 and PM10 samples for megalopolis atmospheric particles were collected at Shinjuku, Tokyo in December 1998–January 1999 and August 1999, for two weeks both in winter and summer, with a 24 hr sampling interval. Sampling of PM2.5 and PM10 in diesel exhaust particles (DEP) was carried out using an automobile exhaust testing system, with a diesel truck placed on a chassis dynamometer. Sampling conditions included idling, constant speed of 40 km hr-1, M-15 test pattern and 60%-revolution/40%-load of maximum power. Mass spectrums of organic compounds adhering to the surface of the PM2.5 and PM10 samples were analyzed by laser desorption time-of-flight mass spectrometry (LD-TOFMS, analytical mass range: m/z 1–m/z 380 000). LD-TOFMS analysis of those samples revealed consistently the detection of low-mass organic compounds up to m/z 800. For the megalopolis atmospheric particles, the mass spectrum pattern of wintertime samples was almost the same as that of the summertime samples for both PM2.5 and PM10. The major peak was m/z 177, and the minor peaks were m/z 84, 94, 101, 163, 189 and 235. The mass spectrum pattern of DEP was the same for all samples under all test conditions. The major peak was m/z 101, and other detected peaks were small. 相似文献
n-Alkanes, polynuclear aromatic hydrocarbons and n-alkanoic acids present in the inhalable fraction of airborne particles have been determined at the Italian scientific base sited in the area of Ny Alesund, Spitzbergen Island, Norway. Both the profiles of n-alkane and polynuclear aromatic congeners among the respective classes showed that anthropogenic sources were responsible for the presence of particulate organics in the atmosphere there, since the monomodal distribution of aliphatics and the fresh-emission shape of PAH fraction were observed. The total contents of n-alkanes and PAH ranged from 19 to 97 ng m−3 and from 0.6 to 2.0 ng m−3, respectively; n-alkanoic acids reached 6 ng m−3. The occurrence of nitrated-PAH of photochemical origin at trace extent (i.e. nitrated-fluoranthenes and nitropyrenes) has been also observed. Since the occurrence of OH radicals is required together with NOx for the processes leading to the generation of 2-nitrofluoranthene and 2-nitropyrene would start, the detection of these nitrated species revealed the occurrence of photochemical processes in that region. 相似文献
