Characterization and Quantitative Assessment of Urban Atmospheric Greenhouse Gases (Co2 and Ch4)-A Case Study of Hong Kong

Abstract

Continuous real-time monitoring of atmospheric CO₂ and CH₄ concentrations at Hong Kong's Cape D'Aguilar Supersite during winter revealed distinct diurnal patterns, with mean levels of 435.29 ± 7.64 ppm and 2083.45 ± 56.50 ppb, respectively. Both gases exhibited bimodal diurnal cycles characterized by morning (CO₂: 436.95 ppm at 05:00; CH₄: 2091.74 ppb at 08:00) and evening peaks (CO₂: 435.80 ppm at 19:00; CH₄: 2084.07 ppb at 18:00), contrasted by afternoon minima (CO₂: 433.63 ppm at 14:00; CH₄: 2075.21 ppb at 11:00), with variations primarily governed by atmospheric boundary layer dynamics. Observed concentrations exceeded those at reference stations in the United States, Japan, South Korea, and Taiwan by 7.76–15.18 ppm (CO₂) and 64.86–144.07 ppb (CH₄), underscoring the region's significance for GHG monitoring. A strong wintertime correlation (r > 0.7) between CO₂ and CH₄ concentrations suggested common emission sources, while wind speed-source distance analysis identified regional transport as the dominant contributor. Quantitative assessment using a meteorological condition - transmission channels - carbon emission (MTE) framework revealed source contributions dominated by Guangdong (55%), Jiangxi (17%), and Jiangsu (12%), with negligible inputs (<0.5%) from Anhui and Henan provinces. These findings emphasize the critical role of sustained GHG observations in coastal megacities for understanding regional emission dynamics and informing climate mitigation strategies.

Keywords: CH4, CO2, meteorological conditions-transmission channels-carbon emission (MTE), planetary boundary layers (PBL), Transportation