Table S1.

Scenarios for sectoral and regional SNG substitution for coal consumption

Substitution scenarios	Substitution strategy
Sectoral
SNG_Power	All SNG used in the power sector
SNG_Industry	All SNG used in the industrial sector
SNG_Residential	All SNG used in the residential sector
Regional
SNG_Region_Sector	SNG allocated to all provinces targeted to receive SNG
SNG_Province	SNG allocated only to provinces with political or economic importance that are targeted to receive SNG†

Under sectoral allocation scenarios, SNG will only be allocated to the specific sector. Under the two regional allocation scenarios, SNG can be allocated to any of the three sectors. Under the medium scenarios, SNG is allocated in each subsector among provinces targeted to receive SNG proportionally to their original gas needs for coal replacement in megajoule units. Original gas needs for coal replacement in each subsector in each SNG targeted province are calculated as: Q_coal,s,p * η_coal,s/η_SNG,s. Q _coal,s,p refers to total baseline coal consumption in subsector s in province p, and η_coal,s and η_SNG,s refer to energy efficiency for coal and gas combustion in subsector s. Under the upper bound scenarios, SNG displaces dirtiest coal first, while under the lower bound scenarios, SNG displaces cleanest coal first. SNG will first be allocated to substitute for coal that brings the largest (smallest) reductions in SO₂ emissions for each unit SNG (grams of SO₂ per cubic meter of SNG used). This takes into account both the SO₂ EFs and the energy efficiencies of coal and SNG combustion.

^†Under the SNG_Province scenario, Inner Mongolia SNG is first allocated to Beijing to satisfy local gas needs; extra gas will then be allocated to Tianjin, and then Hebei and other provinces, due to the political importance of Beijing. Xinjiang SNG is allocated equally to Guangdong, Zhejiang, and Shandong provinces as these three provinces have the highest GDP among provinces targeted to receive Xinjiang’s SNG (1).