Abstract
Cyclic volatile methylsiloxanes (cVMS) and short-chain chlorinated paraffins (SCCPs) use has been restricted in recent years due to environmental health concerns. Both of these classes of emerging contaminants possess long range transport potential (LRTP), highlighting the need for continuous monitoring to assess effectiveness of implemented regulations. However, emission source elucidation and understanding processes affecting atmospheric transport remain challenging. Atmospheric levels of cVMSs and SCCPs were simultaneously monitored at a background monitoring site in Norway from January–July 2020. Concentrations obtained from active air samplers ranged from 49.9 to 845 (mean: 208) pg/m3 for ƩSCCPs and from 0.4 to 3.5 (mean: 1.5), 1.1–15 (mean: 5.6) and 0.1–0.9 (mean: 0.4) ng/m3 for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6), respectively. As SCCPs pose several challenges to analysts, different quantification methodologies and blank handling procedures were investigated to ensure reliable environmental measurements. Simulations using a Lagrangian atmospheric transport model (FLEXPART) revealed air masses impacting sampling measurements were of Oceanic origin, but periodic emission events from Europe and Russia were also observed. Seasonal pattern in cVMS concentrations was mainly driven by atmospheric degradation via hydroxyl radical reaction, whereas SCCP concentrations were more influenced by periodic anthropogenic inputs from local and continental Europe. No clear correlation could be observed with SCCP atmospheric concentrations and temperature over the entire sampling campaign. However, increased volatilization at elevated temperatures may be important with emissions originating from local sources. Higher chlorinated homologue groups dominated during the winter season and declined towards spring and summer, whereas reverse was found for the lower and more volatile chlorinated homologue groups.
| Original language | English |
|---|---|
| Article number | 119754 |
| Pages (from-to) | 1-9 |
| Number of pages | 9 |
| Journal | Atmospheric Environment |
| Volume | 304 |
| Early online date | 12 Apr 2023 |
| DOIs | |
| Publication status | Published - 1 Jul 2023 |
Bibliographical note
Funding Information:Financial support for this study was provided by the Norwegian Ministry of Climate and Environment through the Strategic Institute Programs, granted through the Norwegian Research Council (Arctic, the herald of Chemical Substances of Environmental Concern, Clean Arctic, project # 117031 ) and the Fram Centre Flagship Program “Hazardous substances – effects on ecosystems and human health” (Project 481/762019 : Screening for Emerging Arctic health Risks to Circumpolar Human populations (SEARCH)). Financial support was also received through the Erasmus+ programme of the European Union. We also thank Chris Lunder and Stephen Platt for CO measurement data from Birkenes station within the framework of ICOS, downloaded via ebas.nilu.no.
Funding Information:
The cVMS oligomer and SCCP concentrations were all above MQL (0.9 ng) in the gaseous samples (Table S2). The seasonal trends in average gas phase concentrations of cVMSs and SCCPs measured at Birkenes are shown in Fig. 2 and listed in Tables S3 and S4. Different seasonal trends in concentration were observed for cVMS and SCCPs. The highest concentrations of cVMS occurred during winter (ranging from 2.0 to 3.5, 7.3 to 15 and 0.4 to 0.9 ng/m3 for D4, D5 and D6, respectively) followed by a decline in concentration towards spring (0.4 to0.9, 1.1 to 2.1 and 0.1 to 0.3 ng/m3 for D4, D5 and D6, respectively) and summer (0.5 to 1.3, 1.3 to 4.6 and 0.1 to 0.4 ng/m3 for D4, D5 and D6, respectively) (Fig. 2, Table S4). The seasonal decline in concentration from winter to summer is attributed to the seasonal increase in hydroxyl radical concentrate and subsequent reaction with cVMS (Krogseth et al., 2013; McLachlan et al., 2010). This is supported by high removal activity of an atmospheric tracer behaving like Hg0 by OH radicals at Birkenes (Fig. S3) with removal activity increasing by late winter (March) and reaching its maxima in summer (July). The removal of a substance scales linear with the rate constant, therefore the Hg0 tracer can be used as a proxy here. The temporal cVMS concentrations are comparable with previous records from Birkenes observatory (Bohlin-Nizzetto et al., 2019) from winter to summer (Table S4) and are in good agreement with those obtained from rural Sweden for seasonal variability in atmospheric concentrations of D5 (McLachlan et al., 2010). Concentrations reported here are approximately 2–3 times higher compared to recent findings reported in the Arctic from the Zeppelin Observatory, Svalbard, Norway (Warner et al., 2020) (Table S4) but follow the same pattern, attributed to seasonal changes in hydroxyl radical mediated degradation together with known emissions scenarios (Krogseth et al., 2013; McLachlan et al., 2010). Recent findings from Saitama, Japan showed the same seasonal variability for D4 and D6, but in contrast, no trend was observed for D5 (Horii et al., 2021). This is likely attributed to high emissions of D5 from the surrounding population within Saitama (7.3 million inhabitants) and that atmospheric inputs are dominating over losses caused by hydroxyl mediated degradation, regardless of the season. Warner et al. (2020) observed greater abundance of D4 compared to D5 in air measurements at Zeppelin station between May to September. This can be attributed to the higher persistence of D4 towards hydroxyl-mediated atmospheric degradation (half-life of D4 (10.6 d) > D5 (6.9 d) ((Xu et al., 2019)) and that Zeppelin Observatory was not impacted by nearby emission sources. Despite Birkenes being a background station, D5 was the dominant cVMS detected with the D5/D4 ratio remaining greater than 1 (i.e., 1.7–3.4) throughout all time points within this study. D5/D4 ratio >1 can be attributed to Birkenes having closer proximity to emission sources within Norway/Europe compared to the Zeppelin Observatory. Similar seasonal patterns observed for cVMS among various locations (McLachlan et al., 2010; Warner et al., 2020) (Table S1) indicates that distribution of cVMS within the atmosphere is uniform and mainly being driven by proximity to emission sources and atmospheric degradation mechanisms. Higher SCCP concentrations during the onset of winter were also observed at Birkenes, but concentrations decreased after February and remained stable until late spring ranging between 49.9 to 85.7 pg/m3 (Fig. 2, Table S3). Little information exists regarding atmospheric degradation of SCCPs via hydroxyl radical reaction. Li et al. (2014) used density functional theory to predict hydroxyl radical reaction rates for SCCPs. Estimates of atmospheric half-lives ranged between 0.4 and 67 days, with chain lengths containing 5–8 chlorines exhibiting longer half-lives. Concentrations increased significantly from the end of spring (85.7 pg/m3) into the beginning of summer (May 27 to June 24) with a maximum concentration of 845 pg/m3. Unlike cVMS, increase in SCCP concentration during spring/summer indicates that atmospheric degradation via hydroxyl radical reaction is of minimal importance. Changes in seasonal temperature will contribute to increasing atmospheric concentrations of SCCPs due to their semi-volatile nature with predicted log Koa of 8.9–12.7 for C10–13Cl5-8 (Endo and Hammer, 2020). However, such changes will be dependent on chain length and chlorination degree. This will be further discussed along with other factors driving the observed SCCP seasonal pattern.Financial support for this study was provided by the Norwegian Ministry of Climate and Environment through the Strategic Institute Programs, granted through the Norwegian Research Council (Arctic, the herald of Chemical Substances of Environmental Concern, Clean Arctic, project #117031) and the Fram Centre Flagship Program “Hazardous substances – effects on ecosystems and human health” (Project 481/762019: Screening for Emerging Arctic health Risks to Circumpolar Human populations (SEARCH)). Financial support was also received through the Erasmus+ programme of the European Union. We also thank Chris Lunder and Stephen Platt for CO measurement data from Birkenes station within the framework of ICOS, downloaded via ebas.nilu.no.
Publisher Copyright:
© 2023 Elsevier Ltd
Funding
Financial support for this study was provided by the Norwegian Ministry of Climate and Environment through the Strategic Institute Programs, granted through the Norwegian Research Council (Arctic, the herald of Chemical Substances of Environmental Concern, Clean Arctic, project # 117031 ) and the Fram Centre Flagship Program “Hazardous substances – effects on ecosystems and human health” (Project 481/762019 : Screening for Emerging Arctic health Risks to Circumpolar Human populations (SEARCH)). Financial support was also received through the Erasmus+ programme of the European Union. We also thank Chris Lunder and Stephen Platt for CO measurement data from Birkenes station within the framework of ICOS, downloaded via ebas.nilu.no. The cVMS oligomer and SCCP concentrations were all above MQL (0.9 ng) in the gaseous samples (Table S2). The seasonal trends in average gas phase concentrations of cVMSs and SCCPs measured at Birkenes are shown in Fig. 2 and listed in Tables S3 and S4. Different seasonal trends in concentration were observed for cVMS and SCCPs. The highest concentrations of cVMS occurred during winter (ranging from 2.0 to 3.5, 7.3 to 15 and 0.4 to 0.9 ng/m3 for D4, D5 and D6, respectively) followed by a decline in concentration towards spring (0.4 to0.9, 1.1 to 2.1 and 0.1 to 0.3 ng/m3 for D4, D5 and D6, respectively) and summer (0.5 to 1.3, 1.3 to 4.6 and 0.1 to 0.4 ng/m3 for D4, D5 and D6, respectively) (Fig. 2, Table S4). The seasonal decline in concentration from winter to summer is attributed to the seasonal increase in hydroxyl radical concentrate and subsequent reaction with cVMS (Krogseth et al., 2013; McLachlan et al., 2010). This is supported by high removal activity of an atmospheric tracer behaving like Hg0 by OH radicals at Birkenes (Fig. S3) with removal activity increasing by late winter (March) and reaching its maxima in summer (July). The removal of a substance scales linear with the rate constant, therefore the Hg0 tracer can be used as a proxy here. The temporal cVMS concentrations are comparable with previous records from Birkenes observatory (Bohlin-Nizzetto et al., 2019) from winter to summer (Table S4) and are in good agreement with those obtained from rural Sweden for seasonal variability in atmospheric concentrations of D5 (McLachlan et al., 2010). Concentrations reported here are approximately 2–3 times higher compared to recent findings reported in the Arctic from the Zeppelin Observatory, Svalbard, Norway (Warner et al., 2020) (Table S4) but follow the same pattern, attributed to seasonal changes in hydroxyl radical mediated degradation together with known emissions scenarios (Krogseth et al., 2013; McLachlan et al., 2010). Recent findings from Saitama, Japan showed the same seasonal variability for D4 and D6, but in contrast, no trend was observed for D5 (Horii et al., 2021). This is likely attributed to high emissions of D5 from the surrounding population within Saitama (7.3 million inhabitants) and that atmospheric inputs are dominating over losses caused by hydroxyl mediated degradation, regardless of the season. Warner et al. (2020) observed greater abundance of D4 compared to D5 in air measurements at Zeppelin station between May to September. This can be attributed to the higher persistence of D4 towards hydroxyl-mediated atmospheric degradation (half-life of D4 (10.6 d) > D5 (6.9 d) ((Xu et al., 2019)) and that Zeppelin Observatory was not impacted by nearby emission sources. Despite Birkenes being a background station, D5 was the dominant cVMS detected with the D5/D4 ratio remaining greater than 1 (i.e., 1.7–3.4) throughout all time points within this study. D5/D4 ratio >1 can be attributed to Birkenes having closer proximity to emission sources within Norway/Europe compared to the Zeppelin Observatory. Similar seasonal patterns observed for cVMS among various locations (McLachlan et al., 2010; Warner et al., 2020) (Table S1) indicates that distribution of cVMS within the atmosphere is uniform and mainly being driven by proximity to emission sources and atmospheric degradation mechanisms. Higher SCCP concentrations during the onset of winter were also observed at Birkenes, but concentrations decreased after February and remained stable until late spring ranging between 49.9 to 85.7 pg/m3 (Fig. 2, Table S3). Little information exists regarding atmospheric degradation of SCCPs via hydroxyl radical reaction. Li et al. (2014) used density functional theory to predict hydroxyl radical reaction rates for SCCPs. Estimates of atmospheric half-lives ranged between 0.4 and 67 days, with chain lengths containing 5–8 chlorines exhibiting longer half-lives. Concentrations increased significantly from the end of spring (85.7 pg/m3) into the beginning of summer (May 27 to June 24) with a maximum concentration of 845 pg/m3. Unlike cVMS, increase in SCCP concentration during spring/summer indicates that atmospheric degradation via hydroxyl radical reaction is of minimal importance. Changes in seasonal temperature will contribute to increasing atmospheric concentrations of SCCPs due to their semi-volatile nature with predicted log Koa of 8.9–12.7 for C10–13Cl5-8 (Endo and Hammer, 2020). However, such changes will be dependent on chain length and chlorination degree. This will be further discussed along with other factors driving the observed SCCP seasonal pattern.Financial support for this study was provided by the Norwegian Ministry of Climate and Environment through the Strategic Institute Programs, granted through the Norwegian Research Council (Arctic, the herald of Chemical Substances of Environmental Concern, Clean Arctic, project #117031) and the Fram Centre Flagship Program “Hazardous substances – effects on ecosystems and human health” (Project 481/762019: Screening for Emerging Arctic health Risks to Circumpolar Human populations (SEARCH)). Financial support was also received through the Erasmus+ programme of the European Union. We also thank Chris Lunder and Stephen Platt for CO measurement data from Birkenes station within the framework of ICOS, downloaded via ebas.nilu.no.
Keywords
- cVMSs
- Emission source elucidation
- Long-range transport (LRT)
- Quantification
- SCCPs
- Seasonal variability
