Source Identification and Apportionment of Non-Methane Hydrocarbons Compounds in Rural Area in France
Non-methane hydrocarbons (NMHC) play an important role in the chemistry of the troposphere considering their key role in ozone production. Both biogenic and anthropogenic sources are known to contribute to their presence in urban atmosphere. But few data are available on their contribution to individual hydrocarbon levels in rural areas and its temporal and spatial variations.
Long term measurements of Ozone (O3), nitrogen oxides (NOx) and NMHC were performed on the three French rural sites, as part of EMEP program.
The examination of the levels and trends showed a global decrease of background NMHC concentrations. These results are in accordance with the trends observed in other studies in Europe and are in agreement with the decrease of NMHC emissions in France as positive consequences of the European directive 99/13/CE. Nevertheless, we observed a slight increase in long-lived species like ethane and propane, associated to the long-range transport. We also noted a pronounced increase in biogenic compounds like isoprene, one of the most reactive species.
Data analysis was also based on receptor modelling using Positive Matrix Factorization (PMF) to characterize NMHC source profiles and their contributions. Moreover, a backward trajectory method was applied to source contributions deduced from PMF in order to locate source regions. By completing this approach with photochemical aging, we can discern formation, removal and long-range transport process. The main goal of this study is to carry out a NMHC data extensive analysis in order to improve the comprehension of the increase trend of background ozone.