Title: Cities, traffic, and CO₂: A multidecadal assessment of trends, drivers, and scaling relationships

Abstract

Emissions of CO₂ from road vehicles were 1.57 billion metric tons in 2012, accounting for 28% of US fossil fuel CO₂ emissions, but the spatial distributions of these emissions are highly uncertain. We develop a new emissions inventory, the Database of Road Transportation Emissions (DARTE), which estimates CO₂ emitted by US road transport at a resolution of 1 km annually for 1980-2012. DARTE reveals that urban areas are responsible for 80% of on-road emissions growth since 1980 and for 63% of total 2012 emissions. We observe nonlinearities between CO₂ emissions and population density at broad spatial/temporal scales, with total on-road CO₂ increasing nonlinearly with population density, rapidly up to 1,650 persons per square kilometer and slowly thereafter. Per capita emissions decline as density rises, but at markedly varying rates depending on existing densities. Here, we make use of DARTE's bottom-up construction to highlight the biases associated with the common practice of using population as a linear proxy for disaggregating national- or state-scale emissions. Comparing DARTE with existing downscaled inventories, we find biases of 100% or more in the spatial distribution of urban and rural emissions, largely driven by mismatches between inventory downscaling proxies and the actual spatial patterns of vehiclemore » activity at urban scales. Here, given cities' dual importance as sources of CO₂ and an emerging nexus of climate mitigation initiatives, high-resolution estimates such as DARTE are critical both for accurately quantifying surface carbon fluxes and for verifying the effectiveness of emissions mitigation efforts at urban scales.« less

Authors:

Gately, Conor K. ^[1]; Hutyra, Lucy R. ^[1]; Sue Wing, Ian ^[1]

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+ Show Author Affiliations

1. Boston Univ., MA (United States). Dept. of Earth and Environment

Publication Date:

Mon Apr 06 00:00:00 EDT 2015

Research Org.:

Boston Univ., MA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1348401

Grant/Contract Number:  

FG02-06ER64204; NNX12AM82G; NNH13CK02C; 1149471; 1430145; 1038907

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 112; Journal Issue: 16; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences, Washington, DC (United States)

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; carbon dioxide; emissions; on-road; transportation; urban