Observation of atmospheric aerosols at Mt. Hua and Mt. Tai in central and east China during spring 2009 – Part 1: EC, OC and inorganic ions

Abstract. PM 10 and size-segregated samples were simultaneously collected at Mt. Hua (2060 m a.s.l.) and Mt. Tai (1545 m a.s.l.) in central and east coastal China during spring, 2009 including an intensive dust storm event occurring on 24 April, and determined for EC, OC and inorganic ions. During the non-dust storm period particles, EC, OC and ions except for SO 4 2− were 2–10 times more abundant at Mt. Tai than at Mt. Hua. SO 4 2− (13 ± 7.1 μg m −3 ) at Mt. Hua was the dominant ion, followed by NO 3 − (5.0 ± 3.9 μg m −3 ), NH 4 + (2.5 ± 1.3 μg m −3 ) and Ca 2+ (1.6 ± 0.8 μg m −3 ). In contrast, at Mt. Tai NO 3 − was most abundant (20 ± 14 μg m −3 ), followed by SO 4 2− (16 ± 13 μg m −3 ), NH 4 + (12 ± 8.9 μg m −3 ) and Ca 2+ (3.9 ± 2.1 μg m −3 ). The fact of NO 3 − exceeding over SO 4 2− at Mt. Tai may suggest the changes in chemical composition of the atmosphere over east China due to sharply increasing vehicle emission. pH values of the water-extracts of PM 10 samples indicate that at the two mountain sites aerosols transported from the south regions are more acidic than those from the north and more acidic at Mt. Tai than at Mt. Hua during the non-dust storm period. During the dust storm event particle mass, OC, Na + , K + , Mg 2+ and Ca 2+ at both sites increased by a factor of 1–9, while EC, NO 3 − and NH 4 + decreased by 20–80 %. However, SO 4 2− concentrations (13 ± 7.7 μg m −3 at Mt. Hua and 15 ± 5.6 μg m −3 at Mt. Tai, respectively) at the two sites during the episode were comparable and did not change significantly compared to those in the non-dust storm period, probably due to a similar level of free tropospheric SO 2 in central and east China. Compared with those at Mt. Hua the coarse modes (>2.1 μm) of K + and SO 4 2− at Mt. Tai during the non-event period were more abundant and the coarse mode of NO 3 − was less abundant. When the dust storm was present all ions significantly moved toward coarse particles, except for NH 4 + , with a disappeared peak in fine mode ( 3 − . Linear regression for ion equivalents in fine particles indicates that ammonium exists in the forms of NH 4 NO 3 and NH 4 HSO 4 at Mt. Hua and NH 4 NO 3 and (NH 4 ) 2 SO 4 at Mt. Tai during both the nonevent and the event periods. While the regression for coarse mode of Ca 2+ suggests a close coupling of dust with nitrate during the nonevent time and with sulfate during the dust-storm period. pH values of the size-resolved samples further suggest that during the nonevent period most acidic particles at Mt. Hua are in the range of 0.7–1.1 μm, while those at Mt. Tai are in the range of 1.1–2.1 μm. Aerosols at both sites became alkaline during the event, but the Mt. Tai particles still showed a lower pH value.