Paolo Ciccioli

Reactive Hydrocarbons in the Atmosphere at Urban and Regional Scales

Publisher Summary In urban and suburban areas where vehicular emissions are the dominant sources of hydrocarbons, olefins and arenes are the most reactive organic components. Together, they may account for about 80% of the ozone production. Particularly important are the C4 to C8 branched and cyclic olefins and dienes and aromatics from xylenes to tetramethylbenzenes. The semivolatile fraction from C8 to C20 can be important in producing ozone in areas, such as many European cities, where diesel emissions account for a significant portion (20 to 40%) of the total hydrocarbon emissions. This chapter discusses the reactivity of hydrocarbons in the atmosphere on the basis of aerometric observations made at different tropospheric sites. The rapid and selective removal from the atmosphere of components capable of reacting rapidly with OH radicals, NO3 radicals, and ozone suggests that photochemical pollution is the main tropospheric sink for hydrocarbons. Examples showing the selective removal of hydrocarbons during photochemical smog episodes are provided in the chapter. Using Rome as a case study, diurnal changes in reactivity and the effects of dilution and transport in an urban plume are also discussed in the chapter. Differences between fluxes and emission rates measured in a forest site are used to assess the reactivity of biogenic hydrocarbons.

Biogenic Volatile Organic Compound Emissions

A GIS-based model was developed so to predict Biogenic Volatile Organic Compounds (BVOCs) emissions from the Italian forest ecosystems in order to estimate the fraction of the Net Primary Production lost as reduced carbon and to assess the impact of BVOCs in the formation of ozone and secondary organic aerosols. The performance of the model was verified by comparing the predictions with BVOC fluxes measured in a CarboItaly site using the gradient method with tethered balloon profiles, but also with BVOC fluxes measured in previous years. The agreement between observations and predictions indicated a rather accurate estimation of the model and confirmed the importance in the Italian peninsula of monoterpene emissions, expecially of the fast reacting sabinene in areas dominated by Fagus sylvatica L. and Castanea sativa L.