Characterization of dust storms to Hong Kong in April 1998

In April 1998, two intense dust storms were generated in Central Asia and transported eastward across East Asia (15 and 19 April). This article presents the chemical characterization of Hong Kong (HK) aerosols during the dust storms. During the 15 April dust storm, hourly respiratory suspended particles (RSP) (particle diameter smaller than 10 μm) concentrations monitored at 7 sites in Hong Kong reached the peak values synchronously between 9 and 11 a.m. on 17 April, in which the highest concentration was 267 μg m^-3. Analysis of the RSP samples showed that concentrations of crustal elements (Ba, Ca, Cd, Cr, Fe, Mg, K⁺) and anthropogenic species (As, Ni, Pb, Zn, NH₄⁺, NO₃^-, SO₄^2- and total carbon) were substantially enhanced. Enhancement of these species was more than a factor of 2 to 14 relative to the non dust period. The total carbon content was high, at 59 μg m^-3 (not including carbonate), and the enrichment factors of As and Pb on 17 April were 122 and 117, respectively. This implied that anthropogenic materials together with mineral dust were transported to HK from Mainland China. Based on material balance calculations, mineral dust contributed 41% to the observed RSP mass on 17 April, which was 2 times that of the nondust sample (22%). From the 5-day backward trajectory analysis, this storm was transported directly from Northwest China to HK. However, there was no corresponding observation for the 19 April dust storm aerosol. Consequently, 15 April storm had stronger impact on HK's atmosphere than 19 April storm. Compared to the HK Air Quality Objective, 15 April dust storm did not cause serious air pollution in HK.