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 C1-C2 halocarbons using gas chromatography-electron capture/mass spectrometric detection. The halocarbon dataset was supplemented with measurements of selected non-methane hydrocarbons (NMHCs), C1-C5 alkyl nitrates, sulfur gases and carbon monoxide to better understand sources and atmospheric processes. The median observed atmospheric mixing ratios of CFCs, halons, CCl4 and CH3CCl3 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 (CH3I, CH3Cl, and CH3Br) 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%).
Highlights
Chlorofluorocarbons (CFCs) and their first- and second-generation replacement products, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), are entirely anthropogenic in origin and were developed in the 1930s and continued evolving through the 1980s for domestic and industrial applications as refrigerants, solvents, propellants, and foam blowing agents
A separate group of bromine-containing halocarbons primarily used as fire suppression agents, undergo similar troposphere-stratosphere transport. This is followed by photolytic production of Br, which is more efficient than Cl on a per-atom basis in destroying stratospheric O3
Global increases in industrially produced ozone depleting substances (ODS) and non-ODS halocarbons from 1750 to 2000 are estimated to exert a positive radiative forcing (RF) of +0.33 ± 0.03 W m−2, corresponding to ~13% of the total RF exhibited by all greenhouses gases (IPCC/TEAP, 2005)
Summary
Chlorofluorocarbons (CFCs) and their first- and second-generation replacement products, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), are entirely anthropogenic in origin and were developed in the 1930s and continued evolving through the 1980s for domestic and industrial applications as refrigerants, solvents, propellants, and foam blowing agents. Because of their chemical inertness, the only realistic sink mechanism of tropospheric CFCs upon their release is transport to the stratosphere. Global increases in industrially produced ODS and non-ODS halocarbons from 1750 to 2000 are estimated to exert a positive RF of +0.33 ± 0.03 W m−2, corresponding to ~13% of the total RF exhibited by all greenhouses gases (IPCC/TEAP, 2005)
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