Assessing black carbon sources with aethalometer data and ambient ΔBC/ΔCO ratios analysis

Black Carbon (BC) is a key component of fine particulate matter (PM_2.5) as it has significant health and climate impacts. This paper examines BC source contributions at two urban sites in the Monterrey Metropolitan Area (MMA), one of Latin America's most polluted urban areas. The proposed approach combines the traditional aethalometer model with ambient ΔBC/ΔCO ratios to refine source attribution estimates. Hourly average air quality data (including BC measurements from aethalometer equipment) and meteorological data were collected over one year from two sites: a suburban upwind site and an urban site downwind of major anthropogenic sources. Preliminary data analysis involved assessing correlations between BC and other pollutants, performing Principal Component Analysis, and exploring BC variation patterns to define the appropriate use of ΔBC/ΔCO ratios as a complement to the aethalometer model. Percentile pairs of ΔBC/ΔCO ratios were used to estimate source contributions, representing "pure" emissions from fossil fuel combustion and biomass burning. The best-fit ratios were identified as 0.4 (fossil fuel) and 17.2 (biomass burning), obtained from the 2.5 and 97.5 percentiles. With this, the estimated biomass-burning Absorption Ångström Exponent was found to be 2.34, higher than the commonly used value of 2 when applying the aethalometer model. This adjustment resulted in a reduction in biomass burning contribution estimates of 6-8%. The integration of the aethalometer model with ambient ΔBC/ΔCO ratios can provide a more accurate regional assessment of BC sources, demonstrating significant variations in BC contributions depending on local emission activities and meteorological conditions.