Introduction

Global warming, population growth, and land use changes are closely interrelated forcings that may cause significant changes in future air quality.

We're employing a comprehensive modeling approach to assess the probable effects of global climate change on US regional air quality.

Our study focuses on the effects of global change on air quality in two regions, the Pacific Northwest and the Northern Midwest.

Research Questions:

• How will global warming affect air quality in the two study regions?
• How will land use change due to increased urbanization, global warming, or intentional management, affect air quality?
• How will fire and fire management affect regional air quality, and regional haze specifically, within these regions?
• What is the significance of Asian emissions in US air quality? And how will global change influence the magnitude of the effect of Asian emissions?
• How sensitive is predicted air quality to globally forced boundary conditions, both meteorological and chemical?
• How sensitive are air quality simulations to changes in emission scenarios, both biogenic and anthropogenic?
• How sensitive are air quality simulations to uncertainties in wildfire projections and to potential land management scenarios?

Modeling System

The modeling system is comprises nested regional scale models within global scale models. The global models predict the general trends relating to global climate change while the regional models refine the changes and reflect the effects on air quality.

The NCAR/DOE PCM global climate model and the NCAR MOZART2 global chemistry models provide initial conditions and time dependent boundary conditions to the MM5 / SMOKE / CMAQ regional air quality modeling system. MM5 is a mesoscale meteorology model; SMOKE is an emissions modeling system; and CMAQ is a multi-scale chemical transport model.

To resolve urban scale details in predicted air quality changes, the regional simulations are further nested down from a 36-km US continental scale to urban scales of 12 and 4 km.

Modeling Approach

The targeted future decade of 2045 - 2055. For comparison and to evaluate the modeling system, we established a contemporary base case simulation for 1990 - 2000. Decade-long simulations are desirable to average out the effects of inter-annual climate variability.

GLOBAL: PCM and MOZART2

• Compare current decade (1990 - 2000) to future decade (2045 - 2055)

REGIONAL: MM5 / SMOKE / CMAQ

• 36 km Continental US long term simulations (1 Ð 5 years)
• 12 km Pacific Northwest and Northern Midwest (selected months)
• 4 km Urban centers (selected short episodes)

Additional sensitivity simulations:

• Changes to projected anthropogenic emissions inventory
• Changes in future fire emissions (land management practices)
• Changes in future biogenic emissions (vegetation and land use variations)

Emission Inventories

Anthropogenic Emissions

Based on National Emissions Trend 1999 (NET99) data from EPA. Future emissions will be projected using emission growth factors from EPAÕs Economic Growth Analysis System (EGAS), the Intergovernmental Panel on Climate Change (IPCC) and the literature.

Biogenic Emissions

A new model, Model of Exchange of Gases between the Atmosphere and Nature (MEGAN), will be used to model over 50 individual biogenic emission species. MEGAN includes improved methods for characterizing land cover type, biomass density and various environmental stress factors. This model also accounts for both long and short term changes in growth environment.

Fire Emissions

A Stochastic Fire Scenario Builder (FSB) will be used to estimate prescribed and wild land fire emissions. Fire occurrences will be located on lands based on projected fire probability distribution functions. The spatial and temporal extent of fires will depend on climatology, land use changes, fire management practices and historical fire records.

Acknowledgement:

This project is funded through the EPA STAR collaborative grant.