A quantitative assessment of distributions and sources of tropospheric halocarbons measured in Singapore

Abstract

This work reports the first ground-based atmospheric measurements of 26 halocarbons in Singapore, an urban-industrial city-state in Southeast (SE) Asia. A total of 166 whole air canister samples collected during two intensive 7 Southeast Asian Studies (7SEAS) campaigns (August-October 2011 and 2012) were analyzed for C-C halocarbons using gas chromatography-electron capture/mass spectrometric detection. The halocarbon dataset was supplemented with measurements of selected non-methane hydrocarbons (NMHCs), C-C alkyl nitrates, sulfur gases and carbon monoxide to better understand sources and atmospheric processes. The median observed atmospheric mixing ratios of CFCs, halons, CCl and CHCCl were close to global tropospheric background levels, with enhancements in the 1-17% range. This provided the first measurement evidence from SE Asia of the effectiveness of Montreal Protocol and related national-scale regulations instituted in the 1990s to phase-out ozone depleting substances (ODS). First- and second-generation CFC replacements (HCFCs and HFCs) dominated the atmospheric halocarbon burden with HFC-134a, HCFC-22 and HCFC-141b exhibiting enhancements of 39-67%. By combining near-source measurements in Indonesia with receptor data in Singapore, regionally transported peat-forest burning smoke was found to impact levels of several NMHCs (ethane, ethyne, benzene, and propane) and short-lived halocarbons (CHI, CHCl, and CHBr) in a subset of the receptor samples. The strong signatures of these species near peat-forest fires were potentially affected by atmospheric dilution/mixing during transport and by mixing with substantial urban/regional backgrounds at the receptor. Quantitative source apportionment was carried out using positive matrix factorization (PMF), which identified industrial emissions related to refrigeration, foam blowing, and solvent use in chemical, pharmaceutical and electronics industries as the major source of halocarbons (34%) in Singapore. This was followed by marine and terrestrial biogenic activity (28%), residual levels of ODS from pre-Montreal Protocol operations (16%), seasonal incidences of peat-forest smoke (13%), and fumigation related to quarantine and pre-shipment (QPS) applications (7%).

Long-range transport patterns into the tropical northwest Pacific during the CAMP<sup>2</sup>Ex aircraft campaign: chemical composition, size distributions, and the impact of convection

“…5b), but the observation frequency of 295 MC air dropped sharply above 750 hPa, consistent with previous modeling studies (e.g., Xian et al, 2013). Such distinct vertical distributions between MC and PSEA air are perhaps due to highly sheared environment during the SWM, generally contributing to distinct air mass sources across different altitudes (Atwood et al, 2013;Sarkar et al, 2018) and varying degrees to which these air masses are processed (Section 3.3).…”

“…The inclusion of a monsoon phase filter more explicitly highlights the temporal aspect of meteorology in the TWNP; however, without this 165 monsoon phase criterion, resulting air mass classifications remain largely unchanged (Section 3.2). Furthermore, to account for regional vertical inhomogeneity (Atwood et al, 2013;Sarkar et al, 2018), our analysis of air mass characteristics differentiates between boundary layer (BL; < 2 km) and free troposphere (FT; > 2 km) (Section 3.3).…”

Measurement report: Long-range transport patterns into the tropical northwest Pacific during the CAMP&lt;sup&gt;2&lt;/sup&gt;Ex aircraft campaign: chemical composition, size distributions, and the impact of convection

“…7c) and SO 2− 4 / CO (Fig. 7d) ratios point to higher hygroscopicity in EA air than MC air (Cheung et al, 2020;Saxena et al, 1995;X. Wang et al, 2017;.…”

Observations of High Levels of Ozone-Depleting CFC-11 at a Remote Mountain-Top Site in Southern China

“…As expected, the CFC-11 levels of the pollution events (418 pptv) at the Nanling site (as a regional background site) were much lower than recent results reported in Chinaʼs southwestern developing cities of Chongqing (600 pptv) and Chengdu (960 pptv), the center of the China “Go West” region. However, at the Nanling site, the observed CFC-11 concentrations during the pollution events were even higher than those observed in developed metropolitan areas in Asia such as Beijing (330 and 270 pptv), , Guangzhou (252 pptv), Hangzhou (260 pptv), Taipei (249 pptv), and Singapore (249 pptv) . One possible reason is that these well-developed cities may have implemented stricter regulations of CFC-11 and have fewer CFC-11 emission sources near the sampling locations.…”