Anthropogenic carbon dioxide in the Portland metropolitan region
Abstract
The Portland metropolitan region, located in the Columbia River Gorge, is the most populous region in Oregon. Greenhouse gas emissions inventories for Multnomah County (population ~710k) estimate 2008 emissions to be 8.5 million metric tons carbon dioxide equivalent, of which CO2 is the dominant source. These inventories suggest that County-wide greenhouse gas emissions are near 1990 levels, despite a 22% growth in population. This contrasts with US National greenhouse gas emissions, which are estimated to have grown ~14% since 1990. Despite this apparent progress, there has been no validation of either emissions inventories for the Portland metropolitan region or their trends in time. We present more than two years of measurements of CO2 at three stationary locations in the Portland metropolitan region: a downtown location on the campus of Portland State University; a residential site in southeast Portland; and a rural station on Sauvie Island, located ~30km northwest of Portland in the Columbia River Gorge. Beginning in July 2009, continuous measurements of CO2 at the sites show considerable variability due to global and regional CO2 sources, sinks and boundary layer meteorology. Here we focus on the enhancement of in-city concentrations above the rural Sauvie Island site (CO2 excess), a difference which averages ~6ppm during upgorge wind conditions. The southeast Portland residential site shows a significant enhancement of ~5ppm in CO2 concentration throughout the day. The downtown site shows a substantial diurnal cycle in CO2 excess with 10-15ppm higher values during the day and negative values for CO2 excess during the early morning hours, the cause of which is not well understood. Both in-city sites show an increase in CO2 excess centered around 7-8 am and 5-6 pm during the two rush-hour periods. To examine spatial variability, measurements of street-level CO2 concentrations were obtained using a mobile instrument mounted in a bike trailer during a summer sampling campaign. These data corroborate fixed sites with daytime CO2 concentrations typically 5-10ppm in excess throughout Portland neighborhoods. Substantially higher enhancements (>20ppm) were found near major roadways and other social and biophysical landscape features when compared to surrounding land uses.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B43B0300R
- Keywords:
-
- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions;
- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0490 BIOGEOSCIENCES / Trace gases