Aerosols and nucleation in Eastern China: first insights from the new SORPES-Station
Abstract. Aerosols and new particle formation were studied in the western part of the Yangtze River Delta (YRD), at the SORPES station of Nanjing University. Air ions in the diameter range 0.8–42 nm were measured using an air ion spectrometer, and a DMPS provided particle number size distributions between 6 and 800 nm. Additionally, meteorological data, trace gas concentrations, and PM2.5 values were recorded. During the measurement period from 18 November 2011 to 31 March 2012, the mean total particle concentration was found to be 23 000 cm−3. The mean PM2.5 value was 90 μg m−3, well above national limits. During the observations, 26 new particle formation events occurred, producing 6 nm particles at a rate of about 1 cm−3 s−1. Typical particle growth rates were between 6 and 7 nm h−1. Ion measurements showed the typical cluster band below 2 nm, with total ion concentrations roughly between 600 and 1000 cm−3. A peculiar feature of the ion measurements were heightened ion cluster concentrations during the nights before event days. At 2 nm, the formation rate of charged particles was only about 0.2% of the total rate, pointing towards an only marginal role of ion-induced nucleation. Based on observations, a simple empirical criterion was deducted to estimate particle formation probability. Dominated by radiation and relative humidity, the criterion can predict the occurrence of particle formation with a 90% accuracy. In a similar fashion, a reasonably accurate estimate of particle formation rates was derived. Combined, these parameters allow for a description of particle formation based on a few basic measured variables.