(TDINCOME)-are suggested recently [18] and are taken here. As Wang and Wang [18] have explained the reason that these two factors are considered in detail, the argument is not repeated here.
The introduction of these two variables is also to help justify the rationale of applying spatial SUR models to investigate the spatialtemporal patterns of biomass consumption. Biomass price is acquired from US Energy Information Administration. The biomass price refers to the price of biomass itself, not the biomass productions' price. The total disposable personal income is acquired from Regional Economic Information System, Bureau of Economic Analysis, US Department of Commerce. The total disposable personal income refers to the sum of the disposable personal income of all the residents of a state, and can better reflect the purchasing power of the consumers of state than income, owing to that it considers the personal current taxes paid to federal, state, and local governments, and represents the income that is available to persons
for spending or saving [18]. BC is in trillion British Thermal Unit (Btu), PRICE is in nominal US dollars per million Btu and TDINCOME is in billions of US dollars.