Sources and environmental effects of glyoxal and methylglyoxal
Background,aim,and scope Glyoxal and methylglyoxal,which are intermediate products of the oxidation of volatile organic compounds(VOCs),are key precursors of ozone(O3)and secondary organic aerosols(SOA).Glyoxal and methylglyoxal have complicated origins and can be emitted directly from a wide range of natural or anthropogenic sources as well as secondarily formed through the oxidation of many VOCs.Therefore,the concentrations and sources of glyoxal and methylglyoxal have clear spatial and temporal variations,which further result in spatial and temporal variations in their environmental effects.This paper reviews studies on the abundance,distribution,sources,and health risks associated with glyoxal and methylglyoxal and their contributions to ozone and secondary organic aerosol formation.This paper,thus,provides basic data and scientific information for a better understanding of the origins,chemical degradation,and environmental effects of glyoxal and methylglyoxal in the atmosphere.Materials and methods We collected the concentration data of glyoxal and methylglyoxal in different environments and laboratory experiments from recent studies,analyzed the spatial and temporal variations in the concentrations of glyoxal and methylglyoxal,investigated their source apportionments,and evaluated the environmental effects based on different parameterization methods and model simulations.Results(1)The distribution of glyoxal and methylglyoxal concentrations was characterized by higher concentrations in developed cities than in underdeveloped areas,higher concentrations in than in the suburbs and villages,high concentrations in the early morning,and low concentrations at midday.(2)Seasonal patterns of glyoxal and methylglyoxal levels vary across different areas.The variations in glyoxal and methylglyoxal concentrations in urban areas were characterized by low concentrations in winter and high concentrations in summer,whereas,glyoxal and methylglyoxal concentrations in rural and mountainous areas were high in summer and low in winter.(3)The primary sources of glyoxal and methylglyoxal emissions include biomass burning,vehicular emissions,and cooking emissions.Secondary formation is the most important source of glyoxal and methylglyoxal,and their key precursors include isoprene,acetone,acetylene,and toluene etc.(4)Glyoxal and methylglyoxal are recognized as important contributors to ozone production based on the analysis of their ozone formation potentials(OFPs).(4)Glyoxal and methylglyoxal contribute significantly to the production of secondary organic aerosols through heterogeneous processes,with irreversible uptake being the dominant contribution pathway.(5)High levels of glyoxal and methylglyoxal can induce cellular damage and glycosylation.This can result in the formation of advanced glycation end products(AGEs),which play important roles in the pathogenesis of diabetes,aging,and neurodegenerative diseases.Discussion(1)The temporal and spatial distributions of glyoxal and methylglyoxal were mainly related to variations in their emissions,abundance of their precursors,and the influence of regional transport.(2)The relative contributions of primary and secondary emissions to the abundances of glyoxal and methylglyoxal remain unclear because of the lack of direct measurements of different emissions.(3)Although heterogeneous processes were found to be the key pathways of glyoxal and methylglyoxal in the formation of secondary organic aerosols,large uncertainties were found for these processes,as they were influenced by factors such as meteorological parameters,concentrations of oxidants,acidity,and composition of aerosols.(4)The health effects of atmospheric glyoxal and methylglyoxal remain unclear,and their exposure pathways need to be further determined,as their atmospheric levels are much lower than those in the experiments investigating their health effects.Conclusions Glyoxal and methylglyoxal have distinct spatial and temporal variations with a wide range of sources,including primary emissions and secondary formation from the oxidation of VOCs.Glyoxal and methylglyoxal are important contributors to ozone and secondary organic aerosols.However,the health effects of glyoxal and methylglyoxal in different atmospheric environments remain unclear.Recommendations and perspectives More field measurements,particularly long-term continuous measurements and emission-based measurements,are needed for an accurate description of seasonal variations in glyoxal and methylglyoxal as well as the contributions of primary emissions.The role of long-range transport in the abundance of glyoxal and methylglyoxal as well as their sources and sinks on the sea surface need to be explored.Furthermore,parametrization and numerical methods are required to better estimate the contributions of glyoxal and methylglyoxal to ozone formation.Finally,experimental studies should be combined with field measurements to better understand the evolution and impact factors of glyoxal and methylglyoxal,respectively.Based on the results of these studies,parameterization and degradation schemes for glyoxal and methylglyoxal in different numerical models are expected to be improved.For their health effects,exposure-response studies are needed to explore the long-term health effects related to different concentrations of glyoxal and methylglyoxal,as well as the epidemiological studies in different atmospheric environments.
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