Abstract
Abstract. The National Air Quality Forecast Capability (NAQFC) operated in the US National Oceanic and Atmospheric Administration (NOAA) provides the operational forecast guidance for ozone and fine particulate matter with aerodynamic diameters less than 2.5 µm (PM2.5) over the contiguous 48 US states (CONUS) using the Community Multi-scale Air Quality (CMAQ) model. The existing NAQFC uses climatological chemical lateral boundary conditions (CLBCs), which cannot capture pollutant intrusion events originating outside of the model domain. In this study, we developed a model framework to use dynamic CLBCs from the Goddard Earth Observing System Model, version 5 (GEOS) to drive NAQFC. A mapping of the GEOS chemical species to CMAQ's CB05–AERO6 (Carbon Bond 5; version 6 of the aerosol module) species was developed. The utilization of the GEOS dynamic CLBCs in NAQFC showed the best overall performance in simulating the surface observations during the Saharan dust intrusion and Canadian wildfire events in summer 2015. The simulated PM2.5 was improved from 0.18 to 0.37, and the mean bias was reduced from −6.74 to −2.96 µg m−3 over CONUS. Although the effect of CLBCs on the PM2.5 correlation was mainly near the inflow boundary, its impact on the background concentrations reached further inside the domain. The CLBCs could affect background ozone concentrations through the inflows of ozone itself and its precursors, such as CO. It was further found that the aerosol optical thickness (AOT) from satellite retrievals correlated well with the column CO and elemental carbon from GEOS. The satellite-derived AOT CLBCs generally improved the model performance for the wildfire intrusion events during a summer 2018 case study and demonstrated how satellite observations of atmospheric composition could be used as an alternative method to capture the air quality effects of intrusions when the CLBCs of global models, such as GEOS CLBCs, are not available.
Highlights
The chemical lateral boundary conditions (CLBCs) are pivotal to the prediction accuracy of regional chemical transportPublished by Copernicus Publications on behalf of the European Geosciences Union.Y
The enhanced gaseous pollutants in the full-chemistry CLBCs increased the photochemical generation of ozone, and the higher ozone appeared along the northcentral boundary (Fig. S1a and b in the Supplement), where GEOS-LBC showed 10 ppbv or higher O3 concentrations compared to the static NGAC-LBC and CMAQ_Base for the altitudes of < 4 km (Fig. S1c)
We examined the influence of CLBCs on the prediction of regional air quality and used surface ozone and PM2.5 observations to verify the impacts
Summary
The chemical lateral boundary conditions (CLBCs) are pivotal to the prediction accuracy of regional chemical transport. The US National Oceanic and Atmospheric Administration’s (NOAA) National Air Quality Forecast Capability (NAQFC), which is currently based on the regional-scale CMAQ model, requires CLBCs for its daily prediction. For non-intrusion events, Tang et al (2007) investigated the sensitivity of regional CTMs to CLBCs and found that the background magnitude of the pollutant concentrations was more important than the variation of the CLBCs for the near-surface prediction over polluted areas. Over the contiguous USA, the northern and western USA are near to the prevailing inflow lateral boundaries where Canadian emissions and long-range transported Asian air masses can affect the chemical background concentrations. The NAQFC runs using both GEOS and NGAC CLBCs are compared to a NAQFC base case with monthly 2006 GEOS-Chem CLBCs for summer 2015 During this period, the Canadian wildfires and Sahara dust storms affected the CONUS domain’s northern and southern regions, respectively. We investigate the method of using satellite-derived CLBCs for pollutant intrusion events when CLBCs of global models may not be available
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