Understanding the modeled ground-level ozone bias over the Southeastern U.S.: The role of soil moisture and regional climate
Abstract
Interactive climate-chemistry models routinely overestimate summer ozone concentrations over the southeastern U.S. by 30-60 ppb. We evaluate the cause of this ozone bias using a high-resolution regional climate-chemistry model (RegCM4-CHEM-MEGAN) for 1994-2008. We conduct three simulations that vary the soil moisture initialization and isoprene-soil moisture feedback. One simulation is initialized with late spring (May) soil moisture from the Global Land Data Assimilation System (GLDAS) and run for each summer without an isoprene emissions soil moisture parameterization. The second simulation uses the GLDAS initialization but allows soil moisture to reduce isoprene emissions. The third simulation is a continuous 15-year simulation with isoprene soil moisture parameterization to investigate the effect of soil moisture initialization on the isoprene-ozone feedback. These simulations are compared against measured ozone, isoprene, and NOx concentrations from the EPA Photochemical Assessment Monitoring Stations (PAMS) to assess whether high model ozone persists across all summers, and to highlight specific environmental conditions under which biases are more pronounced. Preliminary results demonstrate that the overestimate of ozone is consistent across all years with average mid-afternoon biases of 54 ppb for July and August and 43 ppb for June in the non-interactive soil moisture-isoprene simulation. Mid-afternoon isoprene concentrations showed similar behavior with greater isoprene concentration biases in the non-interactive run. Turning on the soil moisture parameterization (simulations 2 and 3) improves the mid-afternoon ozone bias by directly decreasing isoprene concentrations. However, the continuous simulation results in root zone soil moisture that is wetter than the GLDAS soil moisture, effectively dampening the impact of summer drying on isoprene emissions reductions and leading to higher ozone concentrations. This highlights the importance of capturing the extent of summer root zone drying and its potential role in improving the systematic summer ozone bias over the southeastern U.S
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.A13K..08T
- Keywords:
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- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions;
- 0345 ATMOSPHERIC COMPOSITION AND STRUCTURE / Pollution: urban and regional;
- 3355 ATMOSPHERIC PROCESSES / Regional modeling;
- Tropospheric Ozone