First long-term study of particle number size distributions and new particle formation events of regional aerosol in the North China Plain
1Key Laboratory for Atmospheric Chemistry, Center for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing 100081, China
2Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
3Shangdianzi Regional GAW station, Research Institute of Urban Meteorology, Beijing Meteorological Bureau, Beijing 100089, China
Abstract. Atmospheric particle number size distributions (size range 0.003–10 μm) were measured between March 2008 and August 2009 at Shangdianzi (SDZ), a rural research station in the North China Plain. These measurements were made in an attempt to better characterize the tropospheric background aerosol in Northern China, one of the currently more polluted regions of the globe. The mean particle number concentrations of the total aerosol, as well as the nucleation, Aitken and accumulation modes were determined to 1.2±0.9×104, 3.6±7.9×103, 4.4±3.4×103 and 3.5±2.8×103 cm−3, respectively. A general finding is that the particle number concentrations were higher during spring compared to the other seasons. The air mass origin had an important effect on the particle number concentration and new particle formation events. Air masses from northwest (i.e. inner Asia) showed the highest concentrations of nucleation mode particles, while southeasterly air masses showed the highest concentrations of accumulation mode particles. 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 formation events, the number concentration of the nucleation mode rose up to maximum values of 104 cm−3. New particle formation events were observed on 36% of the measurement days. The formation rate ranged between 0.7 and 72.7 cm−3 s−1, with a mean value of 8.0 cm−3 s−1. The values of the nucleation mode growth rate ranged between 0.3 and 14.5 nm h−1, with a mean value of 4.3 nm h−1. It is an 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 were usually followed by a measurable increase in total particle mass concentration and extinction coefficient, indicative of a high abundance of condensable vapors in the atmosphere under study.