First long-term study of particle number size distributions and new particle formation events of regional aerosol in the North China Plain
Atmospheric particle number size distributions (size range 0.003–10µm) were measured between March 2008 and August 2009 at Shangdianzi (SDZ), a rural re-search station in the North China Plain. These measurements were made in an attempt to better characterize the tropo-spheric background aerosol in Northern China. The mean particle number concentrations of the total particle, as well as the nucleation, Aitken, accumulation and coarse mode were determined to be 1.2 ± 0.9 × 10 4 , 3.6 ± 7.9 × 10 3 , 4.4 ± 3.4 × 10 3 , 3.5 ± 2.8 × 10 3 and 2 ± 3 cm −3 , respec-tively. A general finding was that the particle number con-centration was higher during spring compared to the other seasons. The air mass origin had an important effect on the particle number concentration and new particle forma-tion events. Air masses from northwest (i.e. inner Asia) fa-vored the new particle formation events, while air masses from southeast showed the highest particle mass concentra-tion. Significant diurnal variations in particle number were observed, which could be linked to new particle formation events, i.e. gas-to-particle conversion. During particle for-mation events, the number concentration of the nucleation mode rose up to maximum value of 10 4 cm −3 . New par-ticle formation events were observed on 36% of the effec-tive measurement days. The formation rate ranged from 0.7 to 72.7 cm −3 s −1 , with a mean value of 8.0 cm −3 s −1 . The value of the nucleation mode growth rate was in the range of 0.3–14.5 nm h −1 , with a mean value of 4.3 nm h −1 . It was an Correspondence to: J. Y. Sun (firstname.lastname@example.org) essential observation that on many occasions the nucleation mode was able to grow into the size of cloud condensation nuclei (CCN) within a matter of several hours. Furthermore, the new particle formation was regularly followed by a mea-surable increase in particle mass concentration and extinction coefficient, indicative of a high abundance of condensable vapors in the atmosphere under study.