Wei et al. Carbon Balance and Management
(2023) 18:1
Page 7 of 10
Table 1 Parameters including the combustion efficiency, charcoal decay rates, disposal rates for end-use wood products, recycling rates for recyclable disposed wood materials, and decay rates for waste wood products used to estimate the carbon stored in wood products made from the timber harvested in Maine, USA, and the carbon stored in the wood products consumed in the United States
Biofuel Biochar
Biofuel and charcoal Combustion efficiency
96%
Charcoal decay (τ) Charcoal decay (σ)
0.007
0.0003
Disposal rate
End-use wood product
α
β
γ
Building
0.133 0.028 0.326 0.041
80 25 30
Exterior use
Home application 0.265 0.031
Newspaper
3.062 0.0 1.006 0.0 6.036 0.0 12.036 0.0
2 6 1
Graphic paper Packing paper
Fig. 4 Disposal rates for building, exterior use, and home application wood products ( a ), the recycling rates for solid waste wood materials (building and home application wood products) and paper products (newspaper, graphic paper, and packing paper) ( b ), and decay rates for waste building, exterior use, home application, and paper wood products in landfills ( c )
Household paper Disposed wood product
0.5
Recycle rate
λ
μ
Building
0.085
0.015 0.016 0.027 0.027 0.027
Home application 0.085
Newspaper
0.225 0.225 0.225
Graphic paper Packing paper
paper recycling regression model, and the parameter- ized model was then employed for all recyclable paper products including newspaper, graphic paper, and pack- ing paper (Table 1; Fig. 4b). To parameterize the decay regression model for waste wood products in landfills, we drew from the results of several prior studies [i.e., 27, 28] [41–43] (Table 1; Fig. 4c). Results The carbon stored in wood products made from the timber harvested in Maine, USA, accumulated to 35.89 Tg C from 1961 to 2019, equivalent to an average annual net sink of 0.61 Tg C (Fig. 5a). In 2019, the paper wood products carbon pool had the smallest accumu- lated size (1.28 Tg C), and the building pool was the largest (16.29 Tg C). Although the average annual pro- duction of paper products was 33.31% of the total wood products, due to the fast turnover rate they formed the smallest end-use wood products carbon pool. The home application carbon pool had the second largest size of 9.03 Tg C. Charcoal had the least annual pro- duction at an average rate of 0.05 Tg C; however, due to its resistant property charcoal was accumulated to a relatively significant stock representing 6.84% (2.45 Tg C) of the estimated total accumulated carbon storage in Maine-harvested wood products over the period of
ω
Landfill decay rate Waste wood material ξ
Building
0.997 1.178
30 20 15
Exterior use
Home application 1.329
Paper
0.821
5
including decay and reburn rates and related parameters were obtained from global studies conducted by Wei et al. [24] and Landry and Matthews [38] (Table 1). The ser- vice half-life for each type of end-use wood product was reviewed from published studies that were conducted in the United States [e.g., 39, 40] (Table 1; Fig. 4a). In the United States, the recycling rate of waste wood materi- als was obtained from the solid wood products recycling data provided by the United States Environmental Pro- tection Agency (EPA). We suggested that the recycling rate of waste wood materials started from 1961 at a rate of 8.5% and increased to be 14.8% in 2020. The data were used to parameterize the recycling rate regression model (Eq. 4). We employed the same recycling regression model for building and home application wood prod- ucts (Table 1; Fig. 4b). According to the EPA paper recy- cling information, the paper recycling rate was estimated as 22.5% in 1961 and significantly increased to a rate of 33.5% in 2020. These rates were used to parametrize the
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