Previous research on atmospheric chemistry in the forest environment has shown that the total reactivity from biogenic volatile organic compound(BVOC) emissions is not well considered in forest chemistry models. One possible explanation for this discrepancy is the unawareness and neglect ofreactive biogenic emissions that have eluded common monitoring methods. This question motivated the development of a total ozone reactivity monitor(TORM) for the direct determination of the reactivity of foliage emissions. Emission samples drawn from a vegetation branch enclosure experimentare mixed with a known and controlled amount of ozone (resulting in, e.g., 100  ppb of ozone) and directed through a temperature-controlledglass flow reactor to allow reactive biogenic emissions to react with ozone during the approximately 2  min residence time in thereactor. The ozone reactivity is determined from the difference in the ozone mole fraction before and after the reaction vessel. An inherentchallenge of the experiment is the influence of changing water vapor in the sample air on the ozone signal. Sample air was drawn through Nafion dryers to mitigate the water vapor interference, and a commercial UV absorption ozone monitor was modified to directly determine the ozone differential with one instrument. Thesetwo modifications significantly reduced interferences from water vapor and errors associated with the determination of the reacted ozone as thedifference from two individual measurements, resulting in a much improved and sensitive determination of the ozone reactivity. This paper provides adetailed description of the measurement design, the instrument apparatus, and its characterization. Examples and results from field deploymentsdemonstrate the applicability and usefulness of the TORM.

In order to establish a creditable greenhouse gas (GHG) monitoringnetwork to support the goals of carbon peak/neutrality, it is necessary toknow what we have done and what we have to do in the future. In this study,we summarize an overview of the status and perspective of GHG monitoring inChina. With decades of effort, China has made a great breakthrough in GHGmonitoring capacity and steadily improved the performance of homemade GHGmonitoring instruments. However, most GHG monitoring studies have beenresearch-oriented, temporal, sparse, and uncoordinated. It is suggested totake full advantage of various monitoring technologies, monitoringplatforms, numerical simulations, and inventory compilation techniques toform a creditable GHG stereoscopic monitoring and assessment system at anoperational level. We envisage that this system can routinely quantify GHGson national, provincial, regional, and even individual scales with highspatiotemporal resolution and wide coverage to support low-carbon policy inChina.

Synthetic halogenated organic chlorofluorocarbons (CFCs) play animportant role in stratospheric ozone depletion and contribute significantlyto the greenhouse effect. In this work, the mid-infrared solar spectrameasured by ground-based high-resolution Fourier transform infraredspectroscopy (FTIR) were used to retrieve atmospheric CFC-11 (CCl 3 F)and CFC-12 (CCl 2 F 2 ) at Hefei, China. The CFC-11 columns observedfrom January 2017 to December 2020 and CFC-12 columns from September 2015 toDecember 2020 show a similar annual decreasing trend and seasonal cycle,with an annual rate of - 0.47 ± 0.06  % yr −1 and - 0.68 ± 0.03  % yr −1 , respectively. So the decline rate of CFC-11 issignificantly lower than that of CFC-12. CFC-11 total columns were higher insummer, and CFC-12 total columns were higher in summer and autumn. BothCFC-11 and CFC-12 total columns reached the lowest in spring. Further, FTIRdata of NDACC (Network for the Detection of Atmospheric Composition Change)candidate station Hefei were compared with the ACE-FTS (Atmospheric Chemistry Experiment Fourier transform spectrometer) satellite data, WACCM(Whole Atmosphere Community Climate Model) data, and the data from otherNDACC-IRWG (InfraRed Working Group) stations (St. Petersburg, Jungfraujoch, and Réunion). Themean relative difference between the vertical profiles observed by FTIR andACE-FTS is - 5.6 ± 3.3  % and 4.8±0.9  % for CFC-11 and CFC-12 for an altitude of 5.5 to 17.5 km, respectively. The results demonstrate that our FTIR data agree relatively well with the ACE-FTS satellite data. The annual decreasing rate of CFC-11 measured from ACE-FTS and calculated by WACCM is - 1.15 ± 0.22  % yr −1 and - 1.68 ± 0.18  % yr −1 , respectively. The interannual decreasing ratesof atmospheric CFC-11 obtained from ACE-FTS and WACCM data are higher thanthat from FTIR observations. Also, the annual decreasing rate of CFC-12 fromACE-FTS and WACCM is - 0.85 ± 0.15  % yr −1 and - 0.81 ± 0.05  % yr −1 , respectively, close to the corresponding values from the FTIR measurements. The total columns of CFC-11 and CFC-12 at the Hefei and St. Petersburg stations are significantly higher than those at the Jungfraujoch and Réunion (Maïdo) stations, and the two values reached the maximum in local summer or autumn and the minimum in local spring or winter at the four stations. The seasonal variability at the three stations in the Northern Hemisphere is higher than that at the station in the Southern Hemisphere.