Variability of aerosol particle number concentrations observed over the western Pacific in the spring of 2009

摘要

Airborne measurements of aerosols were conducted over the western Pacific in the spring of 2009 during the Aerosol Radiative Forcing in East Asia (A-FORCE) aircraft campaign. The A-FORCE flights intensively covered an important vertical-latitudinal range in the outflow region of East Asia (0–9 km altitude; 27°N–38°N). This paper presents the variability of aerosol particle number concentrations obtained by condensation particle counters and a Single-Particle Soot Photometer (SP2), with the focus on those in the free troposphere. The number concentration data include total condensation nuclei with particle diameters (d_p) larger than 10nm (total CN_(10)), PM_(0.17)-CN_(10) (d_p ~10–130 nm), and SP2 black carbon (N_(BC); d_p ~75–850 nm). Large increases in total CN_(10) that were not associated with N_(BC) were observed in the free troposphere, suggesting influences from new particle formation (NPF). Statistical characteristics of total CN_(10), PM_(0.17)-CN_(10), and N_(BC) in the lower troposphere (LT; 0–3 km), middle troposphere (MT; 3–6 km), and upper troposphere (UT; 6–9 km) are investigated. The correlation between total CN_(10) and N_(BC), along with the ratio of PM_(0.17) to total CN_(10) and carbon monoxide mixing ratio (CO), is used to interpret the observed variability. The median concentrations of total CN_(10) and PM_(0.17)-CN_(10) in the UT were higher than those in theMT by a factor of ~1.4 and ~1.6, respectively. We attribute the enhancements of CN_(10) in the UT to NPF. Possible mechanisms affecting NPF in the free troposphere are discussed.