Schenley Park to C.R. Park: Exploring Air Pollution, Energy, and Climate in Pittsburgh and New Delhi

The lack of widespread ambient monitoring, their high spatial variability, and correlations with multiple co-emitted pollutants make long-term health impacts studies of ultrafine particles (UFPs), particles with diameters less than 100 nm (0.1 μm), difficult. Consequently, chemical transport models (CTMs) can help evaluate scientific understanding of UFPs and quantify human exposure.

In this work, we deploy a state-of-the-science CTM, PM-CAMx-UF at high resolution (1 km) over Pittsburgh in winter and summer to simulate UFP concentrations and explore the model’s ability to resolve intraurban spatial and temporal variability in UFP concentrations. We evaluate model predictions against an extensive intraurban network of ~30 long-term UFP and ~50 other pollutant observations sites. Simulations quantify the sources of UFPs within an urban area, and we assess the value-added from increasing model resolution to 1 km. Model inputs include particle number emissions derived from source-specific particle size distributions. Moreover, for traffic sources, we derive spatially resolved emissions from a traffic model for Pittsburgh.

Baseline simulations for February and July 2017 indicate predicted particle number concentrations (PNC) in Pittsburgh vary by more than a factor of two at 1-km resolution, with similar levels of intraurban and urban-rural variability in both winter and summer. Comparisons to a network of 27 long-term (~1 month) winter observation sites in Pittsburgh show model spatial agreement with MFB = -42% and MFE = 42% with better agreement at local road or urban background sites than sites impacted by local sources or topography. Temporally, the model matches winter diurnal variability in PNC at 12 sites with r2 values of monthly average observations and predictions exceeding 0.28 spread across all site types. While on-road traffic contributes to intraurban UFP concentrations in both seasons (~16% winter, ~4% summer), other primary sources such as off-road mobile sources and stationary combustion rival traffic’s contribution.