RESUMO
This work presents the results obtained when determining the priority polycyclic aromatic hydrocarbon (PAH) concentration contained in particulate matter 10 microm in aerodynamic diameter or less (PM10) and in the gas phase in Mexico City's atmosphere by means of a field study conducted during 2005. PM10 and vapor-phase PAHs were collected on prebaked quartz fiber filters and PUF-XAD-4 resin and quantified by gas chromatography (GC)-mass spectrometry. Vapor-phase PAHs comprised 86-97% of the total PAH mass, and naphthalene was the most abundant PAH determined, contributing 84-93% to the total mass. The benzo[a]pyrene content was on average 7% of the PAHs' particle phase and 0.2-1% of the gas phase. The PAH concentrations measured where large industrial areas are located were 2-8 times greater during the fall/winter months (dry-cold season), when winds bear north- northeasterly, than in spring and summer. In contrast, the largest partition gas/particle ratio occurred during the dry-warm season (March-May). The results of statistical analysis using multivariate techniques suggest that motor vehicles are the main PAH contributors. The toxicity equivalence factors (TEFs) related to the carcinogenic benzo[a]pyrene potency were used for the assessment of the carcinogenic potential risk because of the measured airborne PAHs. Benzo[a]pyrene equivalent (BAPeq) concentrations were determined through multiplication of the individual PAH concentrations by their corresponding TEF value. The estimated total BAPeq for the whole field study considering only PM10 PAHs was 1085 pg m(-3). However, when taking into account the PAHs in both phases, the estimated total BAPeq was 1250 pg m(-3); in either case, the values were greater than the 1000-pg m(-3) limit proposed by European countries.
Assuntos
Poluentes Ocupacionais do Ar/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , Estações do Ano , Benzo(a)pireno/análise , Poluentes Ambientais/análise , Cromatografia Gasosa-Espectrometria de Massas , México , Material Particulado/análise , Controle de Qualidade , TemperaturaRESUMO
Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 microg/m3 in PM10 and 0.76 microg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2 x 6H2O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NO(y) species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at approximately 7 am.