Abstract
Abstract. Particle number size distributions in size range 12–570 nm were measured continuously at Mount Waliguan, a remote mountain-top station in inland China. The station is located at the altitude of 3816 m a.s.l., and some 600–1200 m above the surrounding area. The measurement period lasted from September 2005 to May 2007. The measurements were verified with independent CPC measurements at the same site. The average particle concentration in ambient conditions was 2030 cm−3, which is higher than the values measured at similar altitude in other regions of the world. On average, the Aitken mode contributed to roughly half of the particle number concentration. The concentrations were found to be higher during the summer than during the winter. The diurnal variation was also investigated and a clear pattern was found for the nucleation mode during all seasons, so that the nucleation mode particle concentration increased in the afternoon. The same pattern was visible in the Aitken mode during the summer, whereas the accumulation mode did not show any level of diurnal pattern during any season. Excluding the nucleation mode, the average day-time particle concentrations were not significantly higher than those measured at night-time, indicating no systematic pattern of change between planetary boundary layer conditions and free troposphere conditions. In air masses coming from east, the number concentration of particles was higher than in other air masses, which indicates that the air mass might be affected anthropogenic pollution east of the station. Also other factors, such as active new-particle formation, keep aerosol number concentrations high in the area.
Highlights
In order to improve our understanding on the climatic and other influences of atmospheric aerosols, we need to have detailed information on the physical, chemical and optical properties of these aerosols (e.g. Diner et al, 2004)
The diurnal variation was investigated and a clear pattern was found for the nucleation mode during all seasons, so that the nucleation mode particle concentration increased in the afternoon
The ratio occasionally reached values up to 5. These extreme cases were typically observed when a large fraction of the particles measured by the differential mobility particle sizer (DMPS) were in the nucleation mode
Summary
In order to improve our understanding on the climatic and other influences of atmospheric aerosols, we need to have detailed information on the physical, chemical and optical properties of these aerosols (e.g. Diner et al, 2004). Since practically all aerosol properties vary greatly in both time and space, multiple approaches to tackle the problem are required. These include large-scale model simulations, usage of various remote sensing techniques and in situ measurements Most long-term aerosol measurements have been conducted in cities and rural areas in Europe and North America in locations that are relatively easy to access. The majority of such measurements have been based on the aerosol mass concentration, because this quantity is normally used in air quality standards. Very few long-term aerosol measurements have been made in South America, Africa or East Asia, and the conducted studies have usually
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