Abundance, composition and source of atmospheric PM2.5 at a remote site in the Tibetan Plateau, China

Abstract

Two months of PM2.5 samples were collected during the summer of 2010 at Qinghai Lake (3200 m a.s.l.) in the northeastern part of the Tibetan Plateau, China and determined for organic compounds, elemental carbon, organic carbon (OC) and inorganic ions to explore the characteristics of aerosols in the continental atmosphere of China. Approximately 100 organic compounds in the samples were detected with an average of 61±36 ng m−3 in total, accounting for 2.6±1.0% of OC. n-Alkanes (19±12 ng m−3), fatty alcohols (12±7.6 ng m−3), polyols and polyacids (7.5±3.6 ng m−3), sugars (6.5±4.8 ng m−3), and biogenic secondary organic aerosols (BSOA) (6.3±4.4 ng m−3) are the major compounds in the samples, while phthalates (1.9±1.2 ng m−3), polycyclic aromatic hydrocarbons (PAHs) (0.7±0.5 ng m−3) and phthalic acids (2.6±1.5 ng m−3) are minor and one to three orders of magnitude lower than those in urban and rural regions over China. Our results showed that 2-methyltetrols in the PM2.5 samples, two key tracers for isoprene photo-oxidation, positively correlated with ambient temperature, which can be explained by enhancements in biogenic emission and photochemical oxidation when temperature increases. However, we also found that 2-methyltetrols in the samples negatively correlated with relative humidity (RH). Aerosol inorganic model (AIM) calculation showed that in situ acidity of the fine particles decreased along with an increase of RH, which results in a decrease in BSOA production due to acid-catalysed particle-phase reactions inefficient under higher RH conditions.