| Biomass burning(BB),particularly open biomass burning events such as land clearing,agricultural waste burning,prescribed burning,field burning,and wildfires,is of global concern for its primary source of pollutant emissions into the atmosphere across the world.It not only had significant impact on regional air quality and human health,but also the biogeochemical cycle on a regional/global scale.The production or concomitant emissions of large quantities of toxic organic pollutants during biomass burning,such as persistant organic pollutants(POPs),would transport across regions and influence larger scale via long-distance transport.Natural molecular markers with “chemical fingerprint” would be released during the combustion of biomass,which can be used to trace the source of BB and to evaluate the diffusion behavior including migration and transformation of BB aerosols in the atmosphere.BB often occurs accidentally and in backcountry,which increases the difficulties of “capturing” fire emissions over time.Indoor biomass burning includes domestic biofuel burning used for cooking and heating which is currently still hard to assess.Therefore,the lack of data on accurate regional field combustion,and comparison information on reliable source-area,it is difficult to obtain the empirical data of biomass combustion types,patterns and their impact on regional environment and health assessments in different regions.Active sampling is expensive,bulky,heavy,electricdriving and high requirements for operators,which is not suitable for synchronous monitoring of intensive sampling on a regional scale.Passive air sampler(PAS)has advantages of the small size,the low cost,the portability,the easy installation,the power-free operation and the convenient maintenance of PAS,making it more applicable for a large-scale and a long-period sampling comparing with active samplers.Polyurethane foam(PUF)disk based on PAS(PUF-PAS)is the most popular PAS type for cross-temporal and cross-regional synchronous sampling and observation.It has been widely used in different regions and worldwide.It can effectively collect gaseous and particulate semi-volatile organic compounds(SVOCs)including polycyclic aromatic hydrocarbons(PAHs)and POPs.However,as for its application in a sampling of molecular tracers of biomass burning in air,to our knowledge,has not been reported.In this study,the feasibility of collecting BB markers by PUF-PAS was explored,and the BB markers and POPs were simultaneously collected by using PUF-PAS on a regional scale.We investigated the temporal and spatial distribution of biomass burning,and the regional impact of POPs from biomass burning.Four regions with different biomass burning characteristics including Indo-China Peninsula,Pakistan,Southwest China and Pearl River Delta of China were selected as the study area.Indo-China Peninsula has the high natural productivity of vegetation,intensive agricultural activities,and frequent and intensive burning of natural and agricultural biomass,which is one of the research hotspots of biomass burning emissions.The biomass burning in Indo-China Peninsula has the characteristics of large emissions,high diversity of burning fuels,relatively intensive burning period,human health impacts,highlighting its comprehensive and representativeness.Therefore,IndoChina Peninsula is considered as an ideal area to carry out research on biomass burning pollution emissions and its impact on environmental effects.Southwest China,which is adjacent to Indo-China peninsula and the local biomass burning frequency is far lower than that of Indo-China peninsula,can be regarded as the receptor area of biomass burning emissions from Indo-China peninsula.Due to the lack of fossil fuel resources in Pakistan,biomass burning is the primary energy supply.Fuelwood,agricultural resides such as straw and cattle dung are the main biomass burning fuel in Pakistan.Pearl River Delta(PRD)has a densely population,which could also be a comparison region since its biomass burning frequency is far lower than those of Indo-China peninsula and Pakistan.The following are the major results:1.First,we established the PUF-PAS approach for collecting BB biomarkers.PUF-PAS sampling rates for individual monosaccharides were calibrated using an active sampler for 92 days,the capture of monosaccharides by the PUF-PAS increased linearly over 73 days,degradation of monosaccharides in PUF-PAS was demonstrated to be negligible,and the final acquired sampling rates were 1.1,1.5,and 1.1 m3/d for levoglucosan,mannosan,and galactosan,respectively.2.Second,PUF-PAS were deployed in the regions of Indo-China Peninsula,Pakistan,Southwest China and Pearl River Delta.Sampling campaign lasted from January to September in 2016 for three deployment periods.The temporal-spatial distribution of atmospheric monosaccharides,saccharides,sterols and lignins were investigated.During the high-incidence season of BB,the emissions of monosaccharides were the highest,while the amounts of saccharides,sterols and lignins in January-April were higher than those in June-September.Indo-China Peninsula had higher amounts of biomarkers than those in comparison regions such as Pearl River Delta and Southwest China.Monosaccharides concentrations were higher in Indo-China Peninsula(10.4-1240 ng/m3)than those of Pakistan(43.8-455 ng/m3),while the situations were contrary for the saccharides and sterols.The amounts of lignins were comparable in both Indo-China Peninsula and Pakistan.Among the countries of Indo-China Peninsula,Laos had the higher amounts of BB biomarkers than the other countries.To explore the influence factors of biomass burning to the concentrations of monosaccharides derived by PUF-PAS in study areas,we take Pearl River Delta for example.There is a clear correlation between the monosaccharide concentrations and the number of MODIS fire activities corresponding to each sampling site during January-April of 2015,revealing that the feasibility of PUFPAS to monitor the regional concentrations of monosaccharides,the monosaccharides collected by PUF-PAS can reflect the sitation of regianl BB during the period.However,no significant correlation was observed between them in July-September,implying that the open BB intensity could not accurately reflect the influence of BB to ground layer,which might be probably related to the JulySeptember meteorological factors and atmospheric conditions including frequent precipitation and high humidity.To explore the source characterization of biomass combustion types in different study regions,a dual-value combination tracing method by the degradation products of cellulose and lignins could be used to qualitatively differenciated the biomass burning source.Mixed biomass combustion emissions affected Indo-China Peninsula,Pakistan,Southwest China and the Pearl River Delta region.The major biomass fuel in Pearl River Delta were arbor,while the other regions were influenced by shrubs3.Last,PAHs,organochlorine pesticides(OCPs)and polychlorinated biphenyls(PCBs)were primarily orginated from biomass combustion byproducts,agricultural and industrial activities,respectively.As the representatives of POPs,PAHs,OCPs and PCBs were selected to investigate the temporal and spatial distribution in Indo-China Peninsula,Pakistan,Southwest China and the Pearl River Delta Region.Take Indo-china Peninsula for example,we explored the relationships between POPs and BB,and evaluate the contribution of BB to POPs.It turns out that BB were related to several congeners of OCPs and PAHs,and PCB-77,101,105,118 and 153.The contribution of BB to PAHs,OCPs and PCBs were 5%,10% and 4%.The potential emission mechanism of PCBs and OCPs from biomass burning were involved by the revolatilization from the residues of soil and plants,and the de novo formation by the precursors containing chlorine and metal catalysts to the biomass fuels.In summary,using PUF-PAS technique to investigate regional BB pollution and the contribution to POPs in the above study regions,not only fill the gaps of BB field monitor on a regional scale,but also provide reliable comparison information on BB for the other regions of the world.It is of great significance to improve understanding of regional BB pollutants emissions and its environmental effects,and to assess the possible impact of BB on the atmospheric environment in Southwest China and South China. |
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