Suspended particulate matter concentrations along the East–West Corridor, Trinidad, West Indies

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Abstract

An air quality sampling program was designed and implemented to collect baseline concentrations of respirable suspended particulates (PM10) over a six-week period from a network of 18 stations along a populated urban corridor. Air was sampled using portable mini-volume samplers operating in the particulate-sampling mode. Daily samples were gravimetrically determined and comparisons made between the results obtained. Daily PM10 values at some locations met and approached the US 24-h ambient PM10 standard value of 150 μg m−3. Mean levels of PM10 ranged between 46–88 μg m−3, the higher mean levels reflected the closeness of these stations to heavy road traffic; a source of airborne particulate matter. While spatial distribution of PM10 was related to the distance from road traffic, temporal variation in PM10 appeared to be principally associated with presence of Sahara dust, delivered to the region by the North Atlantic Trade Winds. Correlations of PM10 data with road traffic counts and meteorological parameters were generally low.

Introduction

PM10 is particulate matter with an aerodynamic diameter of 10 μm or less. Particles of this size settle very slowly and stay suspended in the air. Medical data suggests that it is this fraction of particulate matter that becomes deeply imbedded in human lung tissue and causes respiratory problems and exacerbates other cardiovascular diseases. In addition to the negative health effects, particulate matter reduces visibility and speeds the deterioration of buildings.

The primary man-made sources of PM10 include fugitive dust from motor vehicles, combustion of solid fuels, agricultural activities, and construction activities. Volcanic emissions, wind blown dust, marine aerosols and fly ash from forest fires are some of the more important natural sources of PM10. Particles can also be formed in the atmosphere by the condensation or the transformation of emitted gases such as sulphur dioxide and volatile organic compounds.

Monitoring of air quality data is used to verify compliance with local and national air quality standards, to support development of regulations designed to reduce air pollution, to assess the effectiveness of existing air pollution control strategies and to provide data on special research projects. The absence of any national air quality standards for Trinidad and Tobago and the paucity of such data provided the impetus for carrying out the present study.

The purpose of the study was to collect baseline PM10 data from a selected area of study, compare the levels found with relevant international standards, analyze the data in terms of temporal and spatial effects and perform correlations between various parameters.

Section snippets

Study area

The study area extended from the town of Arima in east Trinidad to the city of Port of Spain in the west bordered by the Eastern Main Road to the north and the Churchill Roosevelt Highway to the south (Fig. 1). This area is known locally as the East–West Corridor and is home to approximately four hundred thousand persons (ca. 1/3 of population of Trinidad and Tobago). This area also contains some of the busiest roadways in the country with many homes in close proximity to such roads.

Sampling sites and sampling intervals

Eighteen

Precision and data capture

The two pairs of collocated samplers indicated good correlation, at stations 15 (r=0.99) and at station 17 (r=0.84) (see Fig. 2). The mean difference between samplers at each collocated site was 0.66 μg m−3 (station 15) and 3.58 μg m−3 (station 17).

Out of the 359 scheduled PM10 sampling (20 measurement days at 18 sites except one day short at station 17), 344 valid samples were collected, with a data capture rate of 96%. Each station had data capture of 85% and greater except at one of the

Conclusions

This study provided valuable baseline data on PM10 levels as it represented the first time such data has been collected in the country. Data capture rate was high and the precision of the results was good. Average PM10 levels at all stations ranged between 46–88 μg m−3 while daily PM10 levels met and approached the US 24-h standard at some locations on certain days. Road traffic and African mineral dust (Sahara Dust) were important sources of PM10 and Sahara dust played an important role in the

Acknowledgements

The author thanks Ms. Erica Claudette John and Ms. Simi Lakhan, both graduate students from the University of the West Indies for their assistance in collecting all the laboratory data for this study. The publication is a result of technical and financial assistance by the United States Environmental Protection Agency (USEPA) office in Seattle Washington, the Pan American Health Organization (PAHO) office in Trinidad and the Environmental Management Authority (EMA) of Trinidad and Tobago.

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