Exploratory analysis of the atmospheric levels of BTEX, criteria air pollutants and meteorological parameters in a tropical urban area in Northeastern Brazil

Abstract

Air pollution is responsible for serious damage to the environment and to the health of the population. The objective of this study was to apply chemometric methods to determine and evaluate the relationships between the atmospheric concentrations of BTEX (benzene, toluene, ethylbenzene and xylene) compounds, criteria air pollutants and meteorological parameters, as well as to identify the type of emission source associated with these pollutants at seven sites in the city of Salvador, Bahia, Brazil during rainy and dry periods. BTEX compounds were monitored using passive samplers with a solvent desorbable adsorbent (activated charcoal) for 14 days and determined by gas chromatography with flame ionization detection. Criteria air pollutants were determined using automatic continuous analyzers and the meteorological parameters by means of multi-parameters sensors. The average data obtained were submitted to multivariate analysis, using principal component analysis (PCA) with varimax rotation and hierarchical cluster analysis (HCA). Some diagnostic ratios between the BTEX species, besides correlation analysis between the pollutants and meteorological parameters were also used to identify the origin of the emissions. The sum of average concentrations of BTEX compounds was lower in the dry period (5.90 ± 3.28 μg m−3) than in the rainy period (7.95 ± 2.95 μg m−3), probably due to higher values of temperature and solar radiation which favor photochemical reactions in the dry period, thereby increasing the rate of removal of the BTEX compounds from the atmosphere. The first three principal components together (PC1, PC2 and PC3) explain 80.1% of the total data variance, with a tendency to separate the samples into two groups, depending on the seasonal period. According to HCA, four main groups were formed with high degrees of similarity. Strong correlations were found among BTEX species, and between these compounds with CO, NO, and NO2, thus indicating a common emission source for these compounds, the vehicular fleet. Toluene/benzene (T/B), m,p-xylene/benzene (m,p-X/B) and o-xylene/benzene (o-X/B) ratios suggested that vehicular emissions constituted the main source of BTEX compounds. PCA and HCA results also confirmed these observations.