Composition of gaseous organic carbon during ECOCEM in Beirut, Lebanon: new observational constraints for VOC anthropogenic emission evaluation in the Middle East.

The relative importance of Eastern Mediterranean emissions is suspected to be largely underestimated compared to other regions worldwide. Here we use detailed speciated measurements of VOCs (volatile organic compounds) to evaluate the spatial heterogeneity of VOC urban emission composition and the consistency of regional and global emission inventories downscaled to Lebanon (EMEP, ACCMIP, and MACCity). The assessment was conducted through the comparison of the emission ratios extracted from the emission inventories to the ones obtained from the hourly observations collected at a sub-urban site in Beirut, Lebanon during summertime and wintertime ECOCEM campaigns. The observed ERs were calculated by two independent methods. ER values from both methods agree very well (difference up to 10%) and are comparable to the ones of the road transport sector from near-field measurements for more than 80% of the species. There is no significant seasonality in ER for more than 90% of the species unlike the seasonality usually observed in other cities worldwide. Regardless of the season, ERs agree within a factor of 2 between Beirut and other representative worldwide cities except for the unburned fuel fraction and ethane. ERs of aromatics (benzene excepted) are higher in Beirut compared to northern post-industrialized countries and even the Middle Eastern city Mecca. The comparison of the observed ER relative to CO and to acetylene as well as the ratios of every NMVOC to each of the other NMVOCs (NMVOC_i) to the ones extracted from ACCMIP and MACCity global emission inventories suggests that the overall speciation of anthropogenic sources for major hydrocarbons that act as ozone and SOA precursors in ACCMIP is reasonably represented. The comparison of the specific road transport ER relative to acetylene derived from near-field measurements to ER from ACCMIP and EMEP emission inventories for road transport sector showed that ER from the road transport sector are usually consistent within a factor of 2 with the regional emission inventory EMEP while xylenes and toluene are underestimated over a factor of 2 by ACCMIP.The observed heterogeneity of anthropogenic VOC emission composition between Middle Eastern cities can be significant for reactive VOC but is not depicted by global emission inventories. This suggests that systematic and detailed measurements are needed in the Eastern Mediterranean Basin in order to better constrain emission inventory. [ABSTRACT FROM AUTHOR]