Dry deposition (downward, upward) concentration study of particulates and water-soluble ionic species during daytime, night-time period at the traffic sampling site of Sha-Lu, Taiwan

Abstract

Ambient suspended particulate (dry deposition, TSP) was collected in the traffic sites Sha-Lu, central Taiwan. In addition, the related water-soluble ionic species (Cl-, NO3(-), SO4(2-), Na+, NH4(+), K+, Mg2+ and Ca2+) were analysed and wind speed, wind direction and temperature were also measured in this study. The downward dry deposition fluxes (averaged 54.07 microg/m2-sec) were about twice that of upward dry deposition fluxes (averaged 26.48 microg/m2-sec) in the daytime period. Furthermore, the average downward dry deposition fluxes (averaged 26.22 microg/m2-sec) were also about twice that of upward dry deposition fluxes (averaged 12.11 microg/m2-sec) in the night-time period. The results showed that the total suspended particulate concentrations of particulate mass in the daytime period (averaged 996.2 microg/m3) were higher than in the night-time period (averaged 560.7 microg/ m3). The results showed that the total suspended particulate concentrations of particulate mass in the daytime period (averaged 996.2 microg/m3) were higher than in night-time period (averaged 560.7 microg/ m3). As for water-soluble ionic species, the average dry deposition order and velocity for downward ionic species were Cl- > Ca2+ > NO3(-) > K+ (2.09 cm/sec > 1.46 cm/sec > 1.46 cm/sec > 1.07 cm/sec) anions during the daytime period. And the average dry deposition order and velocity for downward ionic species were NO3(-) > Cl- > K+ > Ca2+ (2.92 cm/sec > 2.74 cm/sec > 0.96 cm/sec > 0.93 cm/sec) anions during the night-time period. The average dry deposition order and velocity for upward ionic species were Cl- > Ca2+ > K+ > Mg2+ (4.69 cm/sec > 0.62 cm/sec > 0.59 cm/sec > 0.55 cm/sec) anions during the daytime period. And the average dry deposition order and velocity for upward ionic species were Cl- > Ca2+ > Mg2+ > K+ (1.65 cm/sec > 0.43 cm/sec > 0.37 cm/sec > 0.33 cm/sec) anions during the night-time period. The results also indicated that the sodium and chloride concentrations in total suspended particulate were highly positively related, indicating that the sea-salt aerosols were the major contributors for these species at this sampling site of central Taiwan.