Estudo dos compostos carbonílicos na atmosfera da cidade de Salvador e riscos à saúde humana.

Abstract

Carbonyl compounds, belonging to the class of oxygenated volatile organic compounds (OVOCs), are pollutants of interest not only for their adverse effects on human health but also for their importance in atmospheric chemistry, given their influence on the oxidizing capacity of the atmosphere and the formation of secondary pollutants, such as tropospheric ozone (O3) and secondary organic aerosols (SOA). Therefore, the objective of this study was to investigate carbonyl compounds (CCs) in the atmosphere of the city of Salvador, Bahia, focusing on their concentrations, risks to human health, identification of sources, contribution to oxidative capacity, and formation of secondary air pollutants. Sampling was carried out in seven locations with heavy vehicular traffic, using passive diffusive samplers containing a fiberglass filter impregnated with a 30 mmol L-1 2,4-dinitrophenylhydrazine solution + 1 mol L-1 glycerol, during dry and rainy seasons. Ten CCs were determined by high-performance liquid chromatography (HPLC) with UV detection at 360 nm. Formaldehyde (FA) and acetaldehyde (AA) were the most abundant compounds, representing approximately 55% and 61% of the total concentration, in the rainy and dry seasons, respectively. FA presented concentrations above the limit (3.30 ìg m-3) established by the Texas Commission on Environmental Quality (TCEQ) for long-term outdoor exposure at all sites in both periods. A clear seasonal variation was observed for FA and AA compounds, with higher concentrations in the dry season, attributed to increased temperature and solar radiation, and consequently increased photochemical activity. The human health risk assessment, conducted through probabilistic analysis with Monte Carlo simulation (MCS) considering different age groups of the population (G1: 0-5 years; G2: 6-19 years; G3: 20-70 years), revealed that the lifetime cancer risk (LCR) values at the 95th percentile for FA and AA exceeded the USEPA lower acceptable risk limit (1.0x10-6) for all groups evaluated. In the case of FA, associated with nasopharyngeal cancer, most LCR values were in the 95th percentile exceeded the WHO upper limit (1.0x10-5). Non-carcinogenic risks, expressed as a hazard index (HI) at the 95th percentile, indicated potential risks (HI > 1) for all age groups. The PMF analysis identified vehicular traffic as the main source, followed by photochemical processes and mixed emissions. PCA associated the first component with traffic and the second with secondary formation. HCA revealed two clusters: locations with strong vehicular influence and locations with a greater photochemical contribution. Analysis of the atmospheric concentration balance showed that CCs are formed by direct emissions and by oxidation of volatile hydrocarbons. Furthermore, they act as relevant precursors of OH• and HO2• radicals, actively participating in the dynamics of oxidative reactions in the atmosphere of Salvador, including the formation of species such as O3, and SOA. FA, AA, acrolein, propionaldehyde, n-butyraldehyde and hexaldehyde contributed up to 99% of the ozone formation potential (OFP). Benzaldehyde was the main contributor to the secondary organic aerosol formation potential (SOAFP), confirming that higher molecular weight aldehydes favour the formation of low-volatility compounds capable of partitioning into the particulate phase. The results reinforce the need for public policies aimed at reducing emissions of unconventional pollutants such as CCs and expanding atmospheric monitoring. Furthermore, they also need to revise Brazilian legislation to introduce air quality standards for these compounds, aiming to mitigate their impacts on public health and air quality in the city of Salvador.