Xiaohu Xiong

Is the amplitude of the methane seasonal cycle changing

Abstract Twelve years of atmospheric CH4 data from a globally distributed set of sampling sites ranging in latitude from 82°N to 90°S are analyzed to determine if a statistically significant trend in the peak-to-peak seasonal cycle amplitude exists. Two analysis methods are used. Agreement between amplitude trends determined by the two methods is reasonable. Trends in amplitude determined from sampling sites of similar latitude are not consistent, except in the high southern latitudes, so we focus on the latitude zone 30–90°S, where CH4 destruction is the primary factor determining the seasonal cycle amplitude. In this high southern hemisphere latitude zone, the trend in seasonal cycle amplitude is not statistically different from zero. Statistical uncertainties in the peak-to-peak seasonal cycle amplitude suggest that the observations are consistent with the change in the amplitude expected due to the increasing burden of atmospheric CH4, but not with an increase in the globally averaged OH concentration.

Atmospheric Fossil Fuel CO2 Traced by Δ14C in Beijing and Xiamen, China: Temporal Variations, Inland/Coastal Differences and Influencing Factors

One year of atmospheric Δ(14)CO2 were observed in 2014 in the inland city of Beijing and coastal city of Xiamen, China, to trace temporal CO2ff variations and to determine the factors influencing them. The average CO2ff concentrations at the sampling sites in Beijing and Xiamen were 39.7 ± 36.1 ppm and 13.6 ± 12.3 ppm, respectively. These contributed 75.2 ± 14.6% and 59.1 ± 26.8% to their respective annual ΔCO2 offsets over background CO2 concentrations. Significantly (p < 0.05) high CO2ff values were observed in winter in Beijing. We did not find any significant differences in CO2ff values between weekdays and weekends. Diurnal CO2ff variations were plainly evident, with high values between midnight and 4:00, and during morning and afternoon rush hours. The sampling site in the inland city of Beijing displayed much higher CO2ff inputs and overall temporal variations than the site in the coastal city of Xiamen. The variations of CO2ff at both sites were controlled by a combination of emission sources, topography, and atmospheric dispersion. In particular, diurnal observations at the urban site in Beijing showed that CO2ff was easily accumulated under the southeast wind conditions.