Establishment of multi-elemental source profiles and chemical mass balance studies of air pollutants for Hong Kong

Abstract

It is well known that particulate particles suspended in air cause harmful effects on humans. To tackle this problem, those corresponding major emission sources of particulate particles must be identified and apportioned. In other words, the composition of particles from the major emission sources must be determined. In this study, samples of soil, street dust, road dust, seawater, diesel vehicles exhaust and gasoline vehicles exhaust were collected and measured to establish representative source profiles for Hong Kong. Measurements of airborne species concentrations of total suspended particulate (TSP) were made from January to February of 2002 at King's Park, Yau Ma Tei (YMT) which is located right next to Mong Kok (MK), which is a district with dense population and heavy traffic in Hong Kong. The soil, street dust, paved road dust, diesel vehicles exhaust, gasoline vehicles exhaust and airborne filter samples were analyzed for elemental concentrations by Energy Dispersive X-Ray Fluorescence (EDXRF). Seawater samples were analyzed by flame atomic absorption spectrometer (FAAS) and ion chromatography (IC). A multivariate technique Factor Analysis (FA) was conducted first to identify the number and nature of the sources contributing to the air pollutants collected at YMT. The Chemical Mass Balance receptor model, CMB8, was then employed to apportion the ambient trace metal concentrations at King's Park to emission sources by the use of established source profiles and collected King's Park ambient data. The results showed that crustal materials (Al, Si, Fe, K, and Ca) were the major components in soil, street dust and paved road dust. Na and C1 were dominant in sea water. Vehicle exhausts contained higher amounts of the trace elements Pb than in both soil and street dusts. The FA identified five sources for the King's Park ambient aerosols, namely, crustal materials (explaining 29.0 % of the variance), sea water (explaining 16.2 % of the variance) and three sources related to vehicles (explaining 32.4 % of the variance). The results from the CMB8 program showed that the main contributions to TSP in the 4-5 YMT samples include soil (21.4 %), dust (12.8 %), diesel vehicles (24.1 %) and gasoline vehicles (19.1 %), while sea water had only a minor contribution (4.7 %). The relationship between the source contributions and wind direction, wind speed, humidity and the concentration of Respirable Suspended Particulates (RSP, particulate matter with aerodynamic diameter less than 10 pm) present in Mong Kok roadside station were analyzed. The results suggested that the change of wind speed and humidity did not affect the source contributions. On the other hand, the nature of aerosols collected at King's Park was strongly influenced by the nearby sources when the sources were in the upwind direction of the sampling site. The results suggested that King's Park was strongly influenced by particles emitted in the area of the Cross Harbour Tunnel, since significantly higher diesel and gasoline contributions were obtained when the wind is from the east regardless of the air pollution index (API) of Mong Kok. The correlation of the RSP concentration at the Mong Kok roadside station with the source contribution of King's Park was also examined. Higher levels of soil and dust contributions were found when the wind direction was southwest and the RSP concentration at the Mong Kok roadside station was high. Similarly, a higher contribution from gasoline vehicles was observed when the wind direction was north and the RSP concentration at the Mong Kok roadside station was high.

Date of Award	2 Oct 2003
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kwan Ngok Peter YU (Supervisor)