Abstract
Abstract. Ethane (C2H6) 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 C2H6 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 ± 1.2 (1σ)% and degrees of freedom (DOFS) of 1.47 ± 0.2 (1σ) in the retrieval of C2H6 tropospheric column-averaged dry-air mole fraction (troDMF) over Hefei, eastern China (32∘ N, 117∘ E; 30 ma.s.l.). The observed C2H6 troDMF reached a minimum monthly mean value of 0.36 ± 0.26 ppbv in July and a maximum monthly mean value of 1.76 ± 0.35 ppbv in December, and showed a negative change rate of −2.60 ± 1.34 % yr−1 from 2015 to 2020. The dependencies of C2H6 troDMF on meteorological and emission factors were analyzed using generalized additive models (GAMs). Generally, both meteorological and emission factors have positive influences on C2H6 troDMF in the cold season (December–January–February/March–April–May, DJF/MAM) and negative influences on C2H6 troDMF in the warm season (June–July–August/September–October–November, JJA/SON). GEOS-Chem chemical model simulation captured the observed C2H6 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 C2H6 troDMF variability over Hefei, respectively. The observed C2H6 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 C2H6 transport inflow and outflow over the observation site is largely related to the midlatitude westerlies and the Asian monsoon system. Reduction in C2H6 abundance from 2015 to 2020 mainly results from the decrease in local and transported C2H6 emissions, which points to air quality improvement in China in recent years.
Highlights
Ethane (C2H6) is an important greenhouse gas and one of the most abundant volatile organic compounds (VOCs) in the atmosphere (Abad et al, 2011; Singh et al, 2001; Steinfeld, 1998)
In order to exclude measurements that were seriously affected by instable weather conditions or by the a priori profile due to low measurement information content under less favorable observational conditions, the Fourier transform infrared (FTIR) measurements saved with a solar intensity variation (SIV) of larger than 10 % or retrievals with total degrees of freedom for signal (DOFS) of less than 0.7 or a root mean square (RMS) of fitting residuals of larger than 2 %, which accounted for 11.2 % of total measurements, were excluded from this study
We introduced a variety of potential meteorological and emission factors into the generalized additive models (GAMs) regression one at a time and performed significance tests based on the Akaike information criteria (AIC) values (Wood and Simon, 2004)
Summary
Ethane (C2H6) is an important greenhouse gas and one of the most abundant volatile organic compounds (VOCs) in the atmosphere (Abad et al, 2011; Singh et al, 2001; Steinfeld, 1998). FTIR time series of C2H6 with different time periods have been reported at many stations for the validation of satellite data or chemical model simulation (Abad et al, 2011; Franco et al, 2015, 2016; Glatthor et al, 2009) or for the evaluation of local air quality and air pollutant transport caused by anthropogenic emission and biomass burning (Angelbratt et al, 2011; Lutsch et al, 2016, 2019; Nagahama and Suzuki, 2007; Rinsland et al, 2002; Simpson et al, 2012; Viatte et al, 2015, 2014; Vigouroux et al, 2012; Zeng et al, 2012; Zhao et al, 2002). We first present and quantify the variability, sources, and transport of C2H6 over densely populated and highly industrialized eastern China using FTIR observation, GEOS-Chem model simulation, and the analysis of the meteorological fields.
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