Comparing Monitoring-Based and Modeling-Based Approaches for Evaluating Black Carbon Contributions from a U.S. Airport

Abstract

Black carbon (BC) is a key component of fine particulate matter that is emitted from aircraft and other combustion sources at airports. Understanding the contribution of aviation activity to ambient BC is important given the projected growth in aviation transport and decrease in emissions from other anthropogenic sources, but there are limitations in the various approaches conventionally used for source attribution. In this study, we evaluate three contrasting approaches to assess the contribution of aviation activity to BC concentrations near a small regional airport in Rhode Island, USA. First, we apply a previously developed regression model utilizing continuous BC concentrations measured at five monitoring sites and predictors such as real-time flight activity (departures and arrivals) and meteorological data, including mixing height, wind speed and direction. Second, we used AERMOD to model all airport sources of BC. Third, we used the Community Multiscale Air Quality (CMAQ) model, a comprehensive chemistry-transport air quality model. We included emissions estimates of all airport activity using an enhanced representation within the lowest 10,000 ft. inclusive of the landing and takeoff (LTO) cycle (the lowest 3,000 ft.) in the modeling system, along with other emissions from all other background sources. Median contribution estimates from the regression model indicate that flight activity contribute to approximately 24–28% of the observed BC concentrations at these five locations. The CMAQ and AERMOD based results show a much smaller contribution, in the range of 2–5% of the observed BC concentrations. We present possible explanations for these discrepancies, using a detailed analysis at different temporal scales at all five locations, and consider possible refinements to each approach. Our findings help to highlight the strengths and weaknesses of various source attribution approaches in the context of aviation emissions and other settings where it is of interest to infer local contributions to ambient concentrations.