Forest Fires Enhance the Emission and Transport of Persistent Organic Pollutants and Polycyclic Aromatic Hydrocarbons from the Central Himalaya to the Tibetan Plateau

Abstract

Forest fires are considered one of the drivers of global carbon and aerosol emissions; however, few studies have focused on the release of persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) from forest fires and their regional impacts. In this study, we estimated the emissions of POPs and PAHs from South Asian forest fires and simulated the atmospheric transport of these fire-emitted pollutants to the Tibetan plateau over the Himalaya. It was found that forest fires on the southern slopes of the central Himalaya contributed 20−30% of atmospheric POPs and PAHs during the nonmonsoon season. Under a forest fire scenario, the transport fluxes of DDTs and PAHs increased by ∼25% and ∼20%, respectively, suggesting that forest fires can enhance the transboundary transport of organic pollutants to remote regions, even breaking the barrier of the Himalaya, the highest mountain range in the world. Considering the growth of large-scale wildfires driven by climatic and anthropogenic influences in recent years, forest fires may redistribute POPs globally and thus weaken the regulatory efficiency of the Stockholm Convention to protect remote/polar regions from POP pollution.

Mapping the Contribution of Biomass Burning to Persistent Organic Pollutants in the Air of the Indo-China Peninsula Based on a Passive Air Monitoring Network

“…This estimated BB contribution value was close to the 15% contribution value of incineration sources to PAH emissions in Kolkata, India, comparable with the BB contribution to PAHs (11%) at a regional background site in East China and vegetation fires to the exposure of PCDDs (1–10%) and PAHs (>10%) in Africa observed by satellite and models . However, it was higher than the estimated BB contribution (6%) of PCBs in a non-metropolitan city of northern India and lower than the contribution of forest fires on the southern slopes of central Himalaya to the atmospheric DDTs and PAHs (20–30%) during non-monsoon season . Other identified factors for PCBs are described in Section S4 of Supporting Information.…”

“…Many POPs have been reported in open-field BB. ,, The concentrations of PCDD/Fs and polybrominated diphenyl ethers (PBDEs) at farm sites were elevated by 6–21 times by rice straw open burning. , Emission factors of 2.6 μg/kg for ∑ 13 PCBs and 0.8 μg/kg for dichlorodiphenyltrichloroethane congeners (DDTs) were reported from subtropical eucalypt forest fires . Moreover, elevated concentrations of polycyclic aromatic hydrocarbons (PAHs), PCBs, and pesticides were found to originate from trans-Pacific and regional BB aerosol undergoing long-range atmospheric transport. ,− …”

“…Previous studies on POP emissions from BB were mostly based on emission factors at the combustion sources ,,, and/or predictions via regional remote sensing data and chemistry-transport models. ,, However, emission factors varied with different local typical vegetation and pre-accumulations of POPs in local plants or soil. Regional BB contributions to airborne POPs have been reported only in Africa and Tibetan Plateau and were estimated using daily global emissions from vegetation fires observed by satellite and models. , The limitations of fire data availability or quality may result in large deviations between the predictions and the measurements in these emissions or contribution estimations . For example, non-open fires and small-scale BB incidents, mostly unresolved by satellites, , may also contribute to regional POPs and may likely have been neglected in emission regulations over the long term.…”

Pixel-Based Long-Term (2001–2020) Estimations of Forest Fire Emissions over the Himalaya

“…These regions have high proximity to the densely populated areas (mainly the Indo-Gangetic plain) of the western to eastern Himalaya (Figure S6). The previous studies based on ground-based and remote sensing-based measures also found a significant association between forest fire episodes and declining air quality over the western Himalayan region [40][41][42], the central Himalaya (Nepal) [79,80], and the eastern Himalaya [81].…”