Global budget of ethane and regional constraints on U.S. sources

[1] We use a 3-D chemical transport model (the GEOS-Chem CTM) to evaluate a global emission inventory for ethane (C2H6), with a best estimate for the global source of 13 Tg yr 1, 8.0 Tg yr 1 from fossil fuel production, 2.6 Tg yr 1 from biofuel, and 2.4 Tg yr 1 from biomass burning. About 80 % of the source is emitted in the Northern Hemisphere. The model generally provides a reasonable and unbiased simulation of surface air observations, column measurements, and aircraft profiles worldwide, including patterns of geographical and seasonal variability. The main bias is a 20%–30% overestimate at European surface sites. Propagation of the C 2H 6 seasonal signal from northern midlatitudes to the equatorial western Pacific and the southern tropics demonstrates the dominance of northern midlatitudes as a source of C 2H 6 worldwide. Interhemispheric transport provides the largest C2H6 source to the Southern Hemisphere (1.7 Tg yr 1), and southern biomass burning provides the other major source (1.0 Tg yr 1). The C 2H 6 emission inventory for the United States from the Environmental Protection Agency (0.6 Tg yr 1) is considerably lower than our estimate constrained by extensive aircraft observations in the continental boundary layer (2.4 Tg yr 1). This appears to reflect a factor 7 underestimate in the fossil fuel source over the south-central United States. Our estimate of C2H6 emissions, together with observed ratios of CH4:C2H6, suggests that CH4 emissions from energy production in the U.S. may be underestimated by as much as 50%–100%

Packaging Support for Low-Income Families: Policy Variation across the United States

This paper addresses a gap in state-level comparative social policy research by analyzing policies that support low-income families with children. Variation in state policy “packages” is measured by considering three characteristics of 11 social programs. Individual measures of policy are found to be weakly and inconsistently inter-correlated at the state level, but when cluster analysis is used to analyze multiple dimensions simultaneously, five clusters or regime types are identified that have distinctive policy approaches. These range from the most minimal provisions, to conservative approaches emphasizing private responsibility, to integrated approaches that combine generous direct assistance with employment support and policies that enforce family responsibility. A comparison of a subset of programs at two points in time (1994 and 1998) suggests that states made substantial changes in cash assistance and taxation policies after the 1996 federal welfare reforms. The magnitude and direction of these changes remained consistent with the state clusters identified in 1994. © 2001 by the Association for Public Policy Analysis and Management.