Evolution of ozone, particulates, and aerosol direct radiative forcing in the vicinity of Houston using a fully coupled meteorology‐chemistry‐aerosol model

TLDR

The study employs a new fully coupled meteorology‑chemistry‑aerosol model to simulate urban‑to‑regional variations in trace gases, particulates, and aerosol direct radiative forcing around Houston over a five‑day summer period, with performance evaluated against extensive measurements from the 2000 Texas Air Quality Study. The model reproduces observed trace gas and particulate distributions and shows that sulfate, organic carbon, and other inorganics dominate particulates, but it underestimates hourly aerosol radiative forcing by 10–50 W m⁻²; incorporating aerosol optical properties improves shortwave radiation predictions by 30–40 W m⁻², and the higher aerosol forcing over Houston and the industrial ship channel aligns with surface measurements, highlighting transport, humidity, secondary organic aerosol, and emission uncertainties as key error sources.

Abstract

A new fully coupled meteorology‐chemistry‐aerosol model is used to simulate the urban‐ to regional‐scale variations in trace gases, particulates, and aerosol direct radiative forcing in the vicinity of Houston over a 5 day summer period. Model performance is evaluated using a wide range of meteorological, chemistry, and particulate measurements obtained during the 2000 Texas Air Quality Study. The predicted trace gas and particulate distributions were qualitatively similar to the surface and aircraft measurements with considerable spatial variations resulting from urban, power plant, and industrial sources of primary pollutants. Sulfate, organic carbon, and other inorganics were the largest constituents of the predicted particulates. The predicted shortwave radiation was 30 to 40 W m −2 closer to the observations when the aerosol optical properties were incorporated into the shortwave radiation scheme; however, the predicted hourly aerosol radiative forcing was still underestimated by 10 to 50 W m −2 . The predicted aerosol radiative forcing was larger over Houston and the industrial ship channel than over the rural areas, consistent with surface measurements. The differences between the observed and simulated aerosol radiative forcing resulted from transport errors, relative humidity errors in the upper convective boundary layer that affect aerosol water content, secondary organic aerosols that were not yet included in the model, and uncertainties in the primary particulate emission rates. The current model was run in a predictive mode and demonstrates the challenges of accurately simulating all of the meteorological, chemical, and aerosol parameters over urban to regional scales that can affect aerosol radiative forcing.