Decoupling peroxyacetyl nitrate from ozone in Chinese outflows observed at Gosan Climate Observatory.

We measured peroxyacetyl nitrate (PAN) and other reactive species such as O₃, NO₂, CO, and SO₂ with aerosols including mass, organic carbon (OC), and elemental carbon (EC) in PM_2.5 and K⁺ in PM_1.0 at Gosan Climate Observatory in Korea (33.17° N, 126.10° E) during 19 October- 6 November 2010. PAN was determined through fast gas chromatography with luminol chemiluminescence detection at 425 nm every 2 min. The PAN mixing ratios ranged from 0.1 (detection limit) to 2.4 ppbv with a mean of 0.6 ppbv. For all measurements, PAN was unusually better correlated with PM_2.5 (Pearson correlation coefficient, γ = 0.79) than with O₃ (γ = 0.67). In particular, the O₃ level was highly elevated with SO₂ at midnight, along with a typical midday peak when air was transported rapidly from the Beijing areas. The PAN enhancement was most noticeable during the occurrence of haze under stagnant conditions. In Chinese outflows slowly transported over the Yellow Sea, PAN gradually increased up to 2.4 ppbv at night, in excellent correlation with a concentration increase in PM_2.5 OC and EC, PM_2.5mass, and PM_1.0 K⁺. The high K⁺ concentration and OC= EC ratio indicated that the air mass was impacted by biomass combustion. This study highlights PAN decoupling with O₃ in Chinese outflows and suggests PAN as a useful indicator for diagnosing continental outflows and assessing their perturbation of regional air quality in northeast Asia. [ABSTRACT FROM AUTHOR]