Source apportionment of PM_2.5 for supporting control strategies in the Monterrey Metropolitan Area, Mexico

ABSTRACT

The Monterrey Metropolitan Area (MMA) in Northeast Mexico has shown high PM_2.5 concentrations since 2003. The data shows that the annual average concentration exceeds from 2 to 3 times the Mexican PM_2.5 annual air quality standard of 12 µg/m³. In a previous work we studied the chemical characterization of PM_2.5 in two sites of the MMA during the winter season. Among the most important components we found ammonium sulfate and nitrate, elemental and organic carbon, and crustal matter. In this work we present the results of a second chemical characterization study performed during the summer time and the application of the chemical mass balance (CMB) model to determine the source apportionment of air pollutants in the region. The chemical analysis results show that the chemical composition of PM_2.5 is similar in both sites and periods of the year. The results of the chemical analysis and the CMB model show that industrial, traffic, and combustion activities in the area are the major sources of primary PM_2.5 and precursor gases of secondary inorganic and organic aerosol (SO₂, NOx, NH₃, and volatile organic compounds [VOCs]). We also found that black carbon and organic carbon are important components of PM_2.5 in the MMA. These results are consistent with the MMA emission inventory that reports as major sources of particles and SO₂ a refinery and fuel combustion, as well as nitrogen oxides and ammonium from transportation and industrial activities in the MMA and ammonium form agricultural activities in the state. The results of this work are important to identify and support effective actions to reduce direct emissions of PM_2.5 and its precursor gases to improve air quality in the MMA. Implications: The Monterrey Metropolitan Area (MMA) has been classified as the most air-polluted area in Mexico by the World Health Organization (WHO). Effective actions need to be taken to control primary sources of PM_2.5 and its precursors, reducing health risks on the population exposed and their associated costs. The results of this study identify the main sources and their estimated contribution to PM_2.5 mass concentration, providing valuable information to the local environmental authorities to take decisions on PM_2.5 control strategies in the MMA.

Funding

The authors gratefully acknowledge the scholarship of PROMEP for the development of this work, the financial support of the Air Quality Research Program at ITESM, and the assistance of the Secretariat for Sustainable Development of the State of Nuevo León at the sampling sites.

Additional information

Notes on contributors

Marco Martínez-Cinco

Marco Martínez-Cinco is an associate professor in the Department of Chemical Engineering at Universidad Michoacana de San Nicolás de Hidalgo in Morelia, Mexico.

Jesús Santos-Guzmán

Jesús Santos-Guzmán is a professor in the School of Medicine at ITESM in Monterrey, Mexico.

Gerardo Mejía-Velázquez

Gerardo Mejia-Velázquez is a professor in the Center for Sustainable Development Technologies at ITESM in Monterrey, Mexico.