Ethane (C.sub.2 H.sub.6) is an important greenhouse gas and plays a significant role in tropospheric chemistry and climate change. This study first presents and then quantifies the variability, sources, and transport of C.sub.2 H.sub.6 over densely populated and highly industrialized eastern China using ground-based high-resolution Fourier transform infrared (FTIR) remote sensing along with atmospheric modeling techniques. We obtained a retrieval error of 6.21 Â± 1.2 (1Ï)% and degrees of freedom (DOFS) of 1.47 Â± 0.2 (1Ï) in the retrieval of C.sub.2 H.sub.6 tropospheric column-averaged dry-air mole fraction (troDMF) over Hefei, eastern China (32.sup." N, 117.sup." E; 30 ma.s.l.). The observed C.sub.2 H.sub.6 troDMF reached a minimum monthly mean value of 0.36 Â± 0.26 ppbv in July and a maximum monthly mean value of 1.76 Â± 0.35 ppbv in December, and showed a negative change rate of -2.60 Â± 1.34 % yr.sup.-1 from 2015 to 2020. The dependencies of C.sub.2 H.sub.6 troDMF on meteorological and emission factors were analyzed using generalized additive models (GAMs). Generally, both meteorological and emission factors have positive influences on C.sub.2 H.sub.6 troDMF in the cold season (December-January-February/March-April-May, DJF/MAM) and negative influences on C.sub.2 H.sub.6 troDMF in the warm season (June-July-August/September-October-November, JJA/SON). GEOS-Chem chemical model simulation captured the observed C.sub.2 H.sub.6 troDMF variability and was, thus, used for source attribution. GEOS-Chem model sensitivity simulations concluded that the anthropogenic emissions (fossil fuel plus biofuel emissions) and the natural emissions (biomass burning plus biogenic emissions) accounted for 48.1 % and 39.7 % of C.sub.2 H.sub.6 troDMF variability over Hefei, respectively. The observed C.sub.2 H.sub.6 troDMF variability mainly results from the emissions within China (74.1 %), where central, eastern, and northern China dominated the contribution (57.6 %). Seasonal variability in C.sub.2 H.sub.6 transport inflow and outflow over the observation site is largely related to the midlatitude westerlies and the Asian monsoon system. Reduction in C.sub.2 H.sub.6 abundance from 2015 to 2020 mainly results from the decrease in local and transported C.sub.2 H.sub.6 emissions, which points to air quality improvement in China in recent years.