CAQIMS - Components, Illinois State Water Survey

Climate and Atmospheric Science

Climate, Air Quality and Impact Modeling System (CAQIMS)

A Basis for Achieving Economic, Societal and Environmental Goals in Illinois

Xin-Zhong Liang
Department of Atmospheric Sciences and Illinois State Water Survey, Institute of Natural Resource Sustainability, University of Illinois
Air Quality Model (AQM)

U.S. ozone concentrations are greatly impacted by transport of pollutants from nearby sources including Mexico and Canada. The differences of summer maximum 8-hour daily average ozone (MDA8) in 2048-2052 projected by CMAQ between with CAM-Chem lateral boundary condition (LBC) and with clean LBC under A1B (Fig. 4a) and A1FI (Fig. 4b) emission scenarios illustrate that the ozone long-range transport from Mexico plays an important role on the air quality in the West, especially under high emission scenario A1FI. The changes of the summer MDA8 transport compared to the present are showed in Fig. 4 under A1B (4c) and A1FI (4d). Although the projected summer MDA8 transport in the 2050s under A1B emission scenario is greatly lower than that in 1995-1999 in the western coast states and mountain area, the adjacent area from Texas northwards Kansas is apparently polluted by more concentrated ozone transported from Mexico (Fig. 4c). Under the A1FI emission scenario, the transport of ozone from Mexico in 2048-2050 significantly increases compared to the present (Fig. 4d). Its impact could reach far northwards U.S.-Canada border by at least 20 ppbv over the Central Plains.

maximum daily 8-hour average ozone concentrations
Figure 4. The differences of summer maximum daily 8-hour average ozone concentrations projected by CMAQ between with CAM-Chem LBC and clean LBC during 20482052 under A1B (a), A1FI (b) scenarios, and their changes compared to the present (1995--1999) under A1B (c) and A1FI (d). (Unit: ppbv)

Caused by climate changes and economic rapid development, the variations of ozone concentration have more and more impacts on human society. And mostly, the regional scale air quality has been thought to become worse in a future climate. Despites the lack of observation, the relationship between MDA8 and the Bermuda High Index (BHI) over the concerned areas, including Eastern U.S, the Midwest, Texas, and CA, are studied in this project. In Fig 5a, the observed relationship demonstrates that the high ozone concentration over the Southeast is associated with high surface air temperature and strong solar radiation caused by reduced cloud, related to Bermuda high. The high BHI possibly results in low ozone concentration from Texas northeastwards the Midwest because of the transport by the strong LLJ to the New England. Meanwhile, the area with positive values over CA is more likely related to photochemical reactions enhanced by the solar radiation. The regional models capture these major features, although some biases still exist in downscaling simulations (Fig. 5b,e). Given the uncertainties in models and the future scenarios, multiple projections by different models under different scenarios are needed to develop robust conclusions about climate impacts on air quality. The future projections of regionally downscaled air quality have been developed by SAQM under B1 and A1FI (Fig. 5c,d), and by CMAQ under A1B and A1FI (Fig. 5f,g) scenarios. The SAQM projections reflect the role of the BHI in the future stronger than in present. The pattern projected by CMAQ is different to the SAQMs in some extents, although the similarities appear in the Southeast, the Southern Plains and west coast. Some differences from CMAQ exist between the projections under A1B and A1FI to either its simulated or the observed pattern.

Geographic distributions of the temporal correlation coefficients
Figure 5. Geographic distributions of the temporal correlation coefficients between the BHI and maximum 8-hour daily average ozone for present and 2050s under different scenarios: OBS (a), SAQM/PGR: SAQM simulation/projection driven by PGR for present (b), B1 (c) and A1FI (d), CMAQ/CGR: CMAQ simulation/projection driven by CGR for present (e), B1 (f) and A1FI (g).

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