Carbon and nitrogen isotopes unravels sources of aerosol contamination at Caribbean rural and urban coastal sites.

The constant increase of anthropogenic emissions of aerosols, usually resulting from a complex mixture from various sources, leads to a deterioration of the ambient air quality. The stable isotope compositions (δC and δN) of total carbon (TC) and nitrogen (TN) in both PM and emissions from potential sources were investigated for first time in a rural and an urban Caribbean costal sites in Cuba to better constrain the origin of the contamination. Emissions from road traffic, power plant and shipping emissions were discriminated by coupling their C and N contents and corresponding isotope signatures. Other sources (soil, road dust and cement plant), in contrast, presented large overlapping ranges for both C and N isotope compositions. δC isotope compositions in the rural (average of -25.4 ± 1.2‰) and urban (average of -24.8 ± 1.2‰) sites were interpreted as a mixture of contributions from two main contributors: i) fossil fuel combustion and ii) cement plant and quarries. Results also showed that this last source is impacting more air quality at the urban site. A strong influence from local wood burning was also identified at the rural site. These conclusions were comforted by a statistical analysis using a conditional bivariate probability function. TN and δN values from the urban site demonstrated that nitrogen in PM was generated by secondary processes through the formation of (NH)SO. The exchange in the (NH)SO molecule between gaseous NH and particle NH under stoichiometric equilibrium may control the observed N enrichment. At low nitrogen concentrations in the aerosols, representing PM with both the highest primary N and lowest secondary N proportions, comparison with the δN of potential sources indicate that emissions from diesel car and power plant emissions may represent the major vectors of primary nitrogen.