Estimate Gaps of Montreal Protocol-Regulated Potent Greenhouse Gas HFC-152a Emissions in China Have Been Explained

1,1-Difluoroethane (HFC-152a) is a hydrofluorocarbon regulated by the Montreal Protocol, and its emissions in China are of concern as China will regulate HFC-152a in 2024. However, no observation-inferred top-down estimates were undertaken after 2017, and substantial gaps existed among previous estimates of China's HFC-152a emissions. Using the atmospheric observations and inverse modeling, this study reveals China's HFC-152a emissions of 9.4 ± 1.7 Gg/yr (gigagrams per year), 10.6 ± 1.8 Gg/yr, and 9.7 ± 1.5 Gg/yr in 2018, 2019, and 2020, respectively. In addition, we display an overall increasing trend during 2011-2020, which is in contrast to the decreasing and steady trend reported by the Emission Database for Global Atmospheric Research (EDGAR) and the Chinese government, respectively. Subsequently, we establish a comprehensive bottom-up emission inventory matching with top-down estimates and thus succeed in explaining the gaps among previous estimates. Furthermore, the contribution of China's emissions to global HFC-152a emission growth increased from 15% during 2001-2010 to >100% during 2011-2020. An emission projection based on our improved inventory shows that the Kigali Amendment (KA) would assist in avoiding 1535.6-4710.6 Gg (251.8-772.5 Tg CO2-eq) HFC-152a emissions during 2024-2100. Our findings indicate relatively accurate China's HFC-152a emissions and provide scientific support for addressing climate change and implementing the KA.

Study on CO data filtering approaches based on observations at two background stations in China

The identification of regional representative carbon monoxide (CO) measurements that are minimally influenced by local sources/sinks is essential to understand the characteristics of atmospheric CO over a certain region. In this study, three commonly used data filtering approaches were applied to atmospheric CO data obtained from 2010/2011 to 2017 at two World Meteorological Administration/Global Atmospheric Programme (WMO/GAW) regional stations (Lin'an, LAN and Shangdianzi, SDZ) in China, to study their applicability for individual stations. The three methods used were the meteorological conditions (MET), statistical approaches (robust extraction of baseline signal, REBS), and the time scale of the CO variations (standard deviations of the running mean, SDM). The results from the three methods displayed almost the same seasonal cycles at LAN but different variations at SDZ. They each extracted similar yearly CO growth rates at LAN, but there was a large difference at SDZ, with values of -10.6 ± 0.5, -2.2 ± 0.1, and - 23.5 ± 0.3 ppb yr^-1 for MET, REBS, and SDM, respectively. The slight decrease observed using REBS at SDZ was mainly due to the biased distribution of CO records, which was a purely statistical method that did not consider topography or meteorological conditions. Thus, the REBS method should be applied cautiously to CO observations at stations like SDZ. The SDM method may overestimate multi-year trends. Among the three approaches, MET may be the most suitable for filtering CO observation records, especially at stations like SDZ with special geographical and meteorological conditions in economically-developed regions.

Thirty Years of Atmospheric CO2 Observations at the Plateau Rosa Station, Italy

The atmospheric background CO2 concentration is a key quantity for the analysis and evaluation of the ongoing climate change. Long-term CO2 observations have been carried out at the high Plateau Rosa mountain station, in the north-western Alps since 1989. The complete time series covers thirty years, and it is suitable for climatological analysis. The continuous CO2 measurements, collected since 1993, were selected, by means of a BaDS (Background Data Selection) filter, to obtain the hourly background data. The monthly background data series was analysed in order to individuate the parameters that characterise the seasonal cycle and the long-term trend. The growth rate was found to be 2.05 ± 0.03 ppm/year, which is in agreement with the global trend. The increased background CO2 concentration at the Plateau Rosa site is the consequence of global anthropic emissions, whereas the natural variability of the climatic system taken from the SOI (South Oscillation Index) and MEI (Multivariate ENSO Index) signals was detected in the inter-annual changes of the Plateau Rosa growth rate.

A regional data assimilation system for estimating CO surface flux from atmospheric mixing ratio observations-a case study of Xuzhou, China

Carbon monoxide (CO) emission inventory data are crucial for air quality control. However, the emission inventories are labor-intensive and time-consuming and generally have large uncertainties. In this study, we developed a new regional data assimilation system (TracersTracker) for estimating the surface CO emission flux from continuous mixing ratio observations using the proper orthogonal decomposition (POD)-based four-dimensional variational (4D-VAR) data assimilation method (POD-4DVar) and a coupled regional model (Weather Research and Forecasting model (WRF) with the Models-3 Community Multi-scale Air Quality (CMAQ) model). This system was applied to estimate CO emissions in Xuzhou city, China. An experiment was conducted with the continuous hourly surface CO mixing ratio observations from 21 monitoring towers in January and July of 2016. The experimental results of the system were examined and compared with the continuous surface CO observations (a priori emission). We found that the retrieved CO emission fluxes were higher than the a priori emission and were mainly distributed in urban and industrial areas, which were 104% higher in January (winter) and 44% higher in July (summer).

Ten years of continuous observations of stratospheric ozone depleting gases at Monte Cimone (Italy)--comments on the effectiveness of the Montreal Protocol from a regional perspective

Halogenated gases potentially harmful to the stratospheric ozone layer are monitored worldwide in order to assess compliance with the Montreal Protocol requiring a phase out of these compounds on a global scale. We present the results of long term (2002-2011) continuous observation conducted at the Mt. Cimone GAW Global Station located on the highest peak of the Italian Northern Apennines, at the border of two important regions: the Po Valley (and the Alps) to the North and the Mediterranean Basin to the South. Bi-hourly air samples of CFC-12, CFC-11, CFC-114, CFC-115, H-1211, H-1301, methyl chloroform, carbon tetrachloride, HCFC-22, HCFC-142b, HCFC-124 and methyl bromide are collected and analysed using a gas chromatograph-mass spectrometer, providing multi annual time series. In order to appreciate the effectiveness of the Montreal Protocol from a regional perspective, trends and annual growth rates of halogenated species have been calculated after identification of their baseline values. A comparison with results from other international observation programmes is also presented. Our data show that the peak in the atmospheric mixing ratios of four chlorofluorocarbons, two halons and two chlorocarbons has been reached and all these species now show a negative atmospheric trend. Pollution episodes are still occurring for species like halon-1211, methyl chloroform and carbon tetrachloride, indicating fresh emissions from the site domain which could be ascribed both to fugitive un-reported uses of the compounds and/or emissions from banks. For the hydrofluorocarbons changes in the baseline are affected by emissions from fast developing Countries in East Asia. Fresh emissions from the site domain are clearly declining. Methyl bromide, for which the Mediterranean area is an important source region, shows, in a generally decreasing trend, an emission pattern that is not consistent with the phase-out schedule of this compound, with a renewed increase in the last two years of pollution episodes.

Observations of long-lived anthropogenic halocarbons at the high-Alpine site of Jungfraujoch (Switzerland) for assessment of trends and European sources

Anthropogenic halocarbons, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), bromocarbons (halons) and long-lived chlorinated solvents have been measured continuously at the high-Alpine site of Jungfraujoch (Switzerland) since January 2000. Chloro- and bromo-containing halocarbons are responsible for the stratospheric ozone depletion and will be globally banned from usage within the next years. With the exception of the stable CFC-12 (CF2 Cl2), all major CFCs and chlorinated solvents show a negative trend in recent years in their background concentrations at Jungfraujoch. HCFCs, as their first-generation substitute, are still increasing with a few percent per year. However, the frequency and the strength of HCFCs pollution events, which are caused by regional European emissions, are already declining. This can be seen as a sign of the impending ban of these gases within the next years in Europe. On the other hand, HFCs as the second-generation substitutes, are increasing with relative rates of at least 10% per year (e.g. almost 5 ppt per year for HFC-134a). An allocation of European sources was attempted by combining measured concentrations with trajectories of air masses reaching the Jungfraujoch during pollution events. Potential source regions could be detected in Italy, France, Spain and Germany.

Localization of source regions of selected hydrofluorocarbons combining data collected at two European mountain stations

Ground-based in situ measurements of hydrofluorocarbons HFC-125, HFC-134a, and HFC-152a, which are regulated under the Kyoto Protocol, are carried out at four European sites within the SOGE (System of Observation of Halogenated Greenhouse Gases in Europe) program. Concentrations measured at the high mountain stations of Jungfraujoch (Switzerland) and Mte Cimone (Italy) together with back-trajectory statistical analysis are used in order to identify potential source regions on a European scale. Combining concentration data recorded at the two sites allows to reduce one of the problem which is inherent to the back-trajectory approach, i.e. the localisation of "ghost" sources in the wake of real sources. In this way, a more reliable picture of the location of European potential source regions is given.