Trends in the elemental composition of fine particulate matter in Santiago, Chile, from 1998 to 2003.

ABSTRACT

Santiago, Chile, is one of the most polluted cities in South America. As a response, over the past 15 yr, numerous pollution reduction programs have been implemented by the environmental authority, Comision Nacional del Medio Ambiente. This paper assesses the effectiveness of these interventions by examining the trends of fine particulate matter ([PM.sub.2.5]) and its associated elements. Daily fine particle filter samples were collected in Santiago at a downtown location from April 1998 through March 2003. Additionally, meteorological variables were measured continuously. Annual average concentrations of [PM.sub.2.5] decreased only marginally, from 41.8 [micro]g/m3 for the 1998-1999 period to 35.4 [micro]g/m3 for the 2002-2003 period. [PM.sub.2.5] concentrations exceeded the annual U.S. Environmental Protection Agency standard of 15 [micro]g/[m.sup.3]. Also, approximately 20% of the daily samples exceeded the old standard of 65 [micro]g/[m.sup.3], whereas approximately half of the samples exceeded the new standard of 35 [micro]g/[m.sup.3] (effective in 2006). Mean [PM.sub.2.5] levels measured during the cold season (April through September) were three times higher than those measured in the warm season (October through March). Particulate mass and elemental concentration trends were investigated using regression models, controlling for year, month, weekday, wind speed, temperature, and relative humidity. The results showed significant decreases for Pb, Br, and S concentrations and minor but still significant decreases for Ni, Al, Si, Ca, and Fe. The larger decreases were associated with specific remediation policies implemented, including the removal of lead from gasoline, the reduction of sulfur levels in diesel fuel, and the introduction of natural gas. These results suggest that the pollution reduction programs, especially the ones related to transport, have been effective in reducing various important components of [PM.sub.2.5]. However, particle mass and other associated element levels remain high, and it is thus imperative to continue the efforts to improve air quality, particularly focusing on industrial sources.

INTRODUCTION

In the last decades, the city of Santiago, Chile, has experienced a rapid urban expansion and economic growth, mostly in the industrial sector. The population of Chile is approximately 14 million, of which approximately 40% (6 million) live in the capital, Santiago. The city is located in the central valley of Chile at an elevation of 520 m (0.3 mi) above sea level and is surrounded by two large mountain ranges, the Andes to the east and the Coastal to the west. Summers are hot and dry, whereas winters tend to be colder and more humid, with frequent thermal inversions. The topography, meteorology, large number of industries (70% of the country's total), high population density, and large vehicle and bus fleet (800,000) all contribute to poor air quality in Santiago. (1) High levels of nitrogen oxides, CO, ozone, particulate matter (PM) less than 2.5 [micro]m ([PM.sub.2.5]), PM less than 10 [micro]m ([PM.sub.10]), polycyclic aromatic hydrocarbons, and black carbon have been measured in this urban center. (2-9)

Previous studies conducted in Chile have found health effects associated with high air pollution levels in Santiago, including daily mortality (10,11) and hospital admissions for respiratory illnesses. (12-14) From a health standpoint, there is evidence that certain chemical components of PM are more likely to be responsible for toxic or adverse health effects. (15) For example, some metals such as iron (Fe), vanadium (V), nickel (Ni), and copper (Cu) can trigger inflammation and cause DNA damage. Organic compounds can act as irritants or can cause mutations, which can result in cancer. Sulfates and nitrates can impair mucociliary clearance and change the bioavailability of metals because of their acidity. Also, elemental carbon can induce lung irritation, enhance epithelial proliferation, and cause fibrosis in the lungs. (15) Furthermore, an epidemiologic study by Laden et al. (16) of mortality in six U.S. cities showed that fine particles from motor vehicle and coal combustion sources were associated with higher mortality outcomes, whereas particles of crustal origin were not associated with increases in mortality. Thus, determining the composition and potential sources of PM in Santiago can help to implement more cost-effective mitigation strategies that target the reduction of the more toxic components of PM. Additionally, a better understanding of the factors that influence air pollution levels, such as meteorology, will also aid policy decisions, because these factors also vary over time.

Since the early 1990s, the Chilean government has taken numerous steps to improve the air quality in the Santiago metropolitan area (e.g., see Jorquera et al. (17)). These measures include car-use bans based on license plate number and mandatory vehicle inspections. Also, new cars are now required to have catalytic converters; emission standards have been set for industrial, nonindustrial, and residential heating sources; and an emissions-trading program has been established. In addition, a large fraction of the old bus fleet has been replaced with cleaner diesel fuel buses, and this effort is expected to continue until the entire fleet is replaced. Recently, two important measures were taken: in 1998, a street cleaning and paving plan was initiated and a tree planting campaign was launched to reduce road dust levels, and in 2001, lead was removed from gasoline and sulfur was reduced from diesel fuel from 1000 parts per million (ppm) to 300 ppm. To assess the effectiveness of these and other measures, the Chilean government established an extensive air pollution monitoring network across the city of Santiago.

The air pollution network in Santiago is supported by the Chilean Ministry of Health and has been in operation since the mid-1980s. This network provides the basis for investigating the spatial and temporal profiles of air pollution levels throughout the metropolitan area and aids in the evaluation of the effectiveness of emission control strategies. Using data from this network, our group has examined trends in [PM.sub.2.5], [PM.sub.10], and PM between 2.5- and 10-[micro]m concentrations over a 12-yr period using regression analyses and controlling for corresponding changes in meteorology during that period. (18) The results from these analyses showed a substantial decrease of 52% in [PM.sub.2.5] concentrations over the 12-yr period examined. Specific trends in the elemental composition of [PM.sub.2.5] were not, however, examined. Thus, in this paper, we focus on the elemental components of [PM.sub.2.5] samples collected in downtown Santiago for the years 1998-2003 using similar regression analyses. In addition, results from this trends analysis are used to help determine the effectiveness of pollution control measures.

EXPERIMENTAL WORK

Sampling and Analysis

[PM.sub.2.5] sampling was conducted at the Parque O'Higgins air quality monitoring station in downtown Santiago. This site is located inside the largest park in the Santiago metropolitan area, close to an amusement park, a rollerblading rink, and a University of Chile campus. More importantly, it is located approximately 0.5 km from a major highway (Route 5, also called the "Panamericana") and near minor pollutant sources, such as mechanic shops, metal works, and other small businesses.

Twenty-four-hour particle samples (midnight to midnight) were collected from April 1998 through March 2003. [PM.sub.2.5] filter samples were collected every day during the cold season (April through September) and every other day during the warm season (October through March). Samples were collected using dichotomous samplers (Andersen Instruments Inc.). Details of sampling and filter weighing can be found elsewhere. (18) Elemental analysis was conducted using X-ray fluorescence on the [PM.sub.2.5] aerosol filter samples (Desert Research Institute). To minimize analytical costs, only a subset of randomly selected filters was selected for elemental analysis. For each month, only six to eight filters were selected, or approximately one sample every fourth day, for a total of 456 filters analyzed across the 5 yr of the study. Blanks represented approximately 10% of the samples. The limit of detection (LOD) was calculated for each element as three times the standard error of the blanks. Only elements that had at least 80% of all reported values above LOD were included in the statistical analysis. A total of 14 elements satisfied these criteria and were, thus, included in the analysis together with [PM.sub.2.5]. These include aluminum (Al), silicon (Si), calcium (Ca), iron (Fe), potassium (K), manganese (Mn), zinc (Zn), sulfur (S), copper (Cu), nickel (Ni), chromium (Cr), lead (Pb), bromine (Br), and selenium (Se). Additionally, meteorological variables such as wind speed, wind direction, temperature, and relative humidity (RH) were measured at the sampling site during particle sampling. However, to obtain complete data on meteorological variables, these data were supplemented from the La Paz air quality monitoring station, located a few kilometers north-northwest of the Parque O'Higgins station.

Data Analysis