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231.
Barbara?BarlettaEmail authorView authors OrcID profile Isobel?J.?Simpson Nicola?J.?Blake Simone?Meinardi Louisa?K.?Emmons Omar?S.?Aburizaiza Azhar?Siddique Jahan?Zeb Liya?E.?Yu Haider?A.?Khwaja Muhammad?A.?Farrukh Donald?R.?Blake 《Journal of Atmospheric Chemistry》2017,74(1):87-113
We investigate the composition of 63 C2-C10 nonmethane hydrocarbons (NMHCs), methane (CH4) and carbon monoxide (CO), in Jeddah, Mecca, and Madina (Saudi Arabia), in Lahore, (Pakistan), and in Singapore. We established a database with which to compare and contrast NMHCs in regions where ambient levels and emissions are poorly characterized, but where conditions are favorable to the formation of tropospheric ozone, and where measurements are essential for improving emission inventories and modeling. This dataset will also serve as a base for further analysis of air pollution in Western Saudi Arabia including, but not limited to, the estimation of urban emissions and long range pollution transport from these regions. The measured species showed enhanced levels in all Saudi Arabian cities compared to the local background but were generally much lower than in Lahore. In Madina, vehicle exhaust was the dominant NMHC source, as indicated by enhanced levels of combustion products and by the good correlation between NMHCs and CO, while in Jeddah and Mecca a combination of sources needs to be considered. Very high NMHC levels were measured in Lahore, and elevated levels of CH4 in Lahore were attributed to natural gas. When we compared our results with 2010 emissions from the MACCity global inventory, we found discrepancies in the relative contribution of NMHCs between the measurements and the inventory. In all cities, alkenes (especially ethene and propene) dominated the hydroxyl radical (OH) reactivity (k OH) because of their great abundance and their relatively fast reaction rates with OH. 相似文献
232.
G. Chen D. Davis J. Crawford B. Heikes D. O'Sullivan M. Lee F. Eisele L. Mauldin D. Tanner J. Collins J. Barrick B. Anderson D. Blake J. Bradshaw S. Sandholm M. Carroll G. Albercook A. Clarke 《Journal of Atmospheric Chemistry》2001,38(3):317-344
Reported are the results from a comparison of OH,H2O2CH3OOH, and O3 observationswithmodel predictions based on current HOx–CH4reaction mechanisms. The field observations are thoserecorded during the NASA GTE field program, PEM-Tropics A. The major focus ofthis paper is on thosedata generated on the NASA P-3B aircraft during a mission flown in the marineboundary layer (MBL) nearChristmas Island, a site located in the central equatorial Pacific (i.e.,2° N, 157° W). Taking advantage of thestability of the southeastern trade-winds, an air parcel was sampled in aLagrangian mode over a significantfraction of a solar day. Analyses of these data revealed excellent agreementbetween model simulated andobserved OH. In addition, the model simulations reproduced the major featuresin the observed diurnalprofiles of H2O2 and CH3OOH. In the case ofO3, the model captured the key observational feature whichinvolved an early morning maximum. An examination of the MBL HOxbudget indicated that the O(1D) + H2Oreaction is the major source of HOx while the major sinks involveboth physical and chemical processes involving the peroxide species,H2O2 and CH3OOH. Overall, the generally goodagreement between modeland observations suggests that our current understanding ofHOx–CH4 chemistry in the tropical MBL isquite good; however, there remains a need to critically examine this chemistrywhen both CH2O and HO2are added to the species measured. 相似文献
233.
T. G. Milligan G. C. Kineke A. C. Blake C. R. Alexander P. S. Hill 《Estuaries and Coasts》2001,24(5):734-744
Extremely rapid deposition of fine-grained sediment has been observed near an artificially created channel between the Edisto and Ashepoo Rivers in South Carolina. Accumulation rates on the order of 0.05 m mo−1 formed a region of fluid mud known as the Mud Reach that was present during a study carried out in May 1998. Subsequent surveys in March and May 1999 found no evidence of fluid mud in this area. Image analysis of photographs of the suspended sediment from 1998 showed that the water column was populated by flocs with a median diameter on the order of 0.3 mm which tended to remain in suspension over the tidal cycle, and flocs on the order of 0.8 mm which remained in the near bottom region except at maximum current speeds. In 1999, both the size and concentration of flocs at the surface remained the same, but the size and abundance of flocs near the bottom was reduced. Disaggregated inorganic grain size analysis of the suspension and samples from a core collected in the Mud Reach indicated that in 1998 the accumulation of material on the bottom was the result of floc settling and that in spite of highu s values, little sorting of this material was occurring. Grain size analysis of samples deeper in the core showed that the rapidly floc-deposited mud was underlain by coarser, well-sorted sediment, confirming that the Mud Reach was a transient feature. The observed flocculation processes may play a significant role in the trapping of fine-grained sediment throughout this region. 相似文献
234.
G. H. Blake Dr. 《GeoJournal》1992,28(3):365-373
International boundaries in the Middle East are less likely to represent a major source of international stress than is generally perceived. Formal treaties exist for 80% of the regions' land boundaries and current political processes seem to be working in favour of the status quo and territorial stability. Regarding maritime boundaries, over 60 such issues have yet to be delimited throughout the region. Of these, the major maritime boundary disputes are concentrated in the Persian Gulf, while the boundary between Greece and Turkey remains a focus of regional conflict in the Mediterranean Basin. Although the function of international boundaries are changing, the delimitation process can be expected to continue in the Middle East. Given political will to resolve problems of delimitation, the ultimate demarcation of boundaries should progress without serious conflict between states in the region. 相似文献
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Sarah Elwood 《Urban geography》2017,38(3):329-331
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