10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Characteristics and Origins of Carbonaceous Aerosols at an Urban Site of Qatar Peninsula
WASIM JAVED, Bing Guo, Minas Iakovides, Qi Ying, Euripides G. Stephanou, Texas A&M University at Qatar
Abstract Number: 1117 Working Group: Carbonaceous Aerosol
Abstract Doha, the capital of Qatar, has the world’s twelfth highest levels of atmospheric particulate matter (PM). However, research has been scarce on the level, composition and sources of aerosol pollution in the city. In this study, mass concentrations of PM, elemental carbon (EC) and organic carbon (OC) fractions as well as ninety individual organic compounds, grouped into PAHs, n-alkanes, hopanes and steranes, were measured in PM2.5 and PM10 filter samples at an urban site in Doha, aiming to establish concentration profiles and quantify the contributions of major sources in the area. Three sets of 24-hr filter samples were collected for each PM2.5 and PM10 mass determination, EC/OC analysis and organics speciation from May to December 2015. The real-time mass concentration of PM and black carbon (BC) were also measured by using a DustTrak aerosol monitor and a 7-channel Aethalometer, respectively.
The 24-hr average PM10 and PM2.5 concentrations (±SD) were 145±70 and 40±15 µg m-3 respectively, about 2-3 times higher than the WHO standards. The average EC in PM2.5 and PM10 were 2.61±1.1 and 3.0±1.3 µg m-3 and that of OC were 1.78 ±1.14 and 6.97 ±4.2 µg m-3, respectively. Temporally, PM and BC mass concentrations exhibited well-defined diurnal variations, comprising of a single prominent peak occurring in the morning (6-7am), and were always higher by a factor of about 1.5 during nighttime than the concentrations during daytime. The average PM2.5/PM10 ratio was 0.30, a value that is typical of urban sites affected by the desert environment, suggesting the dominance of coarser particles.
It was found that total carbonaceous contents accounted for 10 to 18% of the PM mass. A dominant fraction (90%) of EC was associated with PM2.5 particles, while about 71% of OC was present in coarser fraction (PM2.5-10), out of which around 68% is in the form of secondary OC. The n-alkanes were the most abundant group followed by PAHs and hopanes, while steranes concentration was the lowest. Long-chain n-alkanes (C25 to C35) accounted for about 90% of the total analyzed n-alkanes with a predominance of odd carbon numbered congeners (C27-C31). High molecular weight PAHs (5-6 rings) accounted for 63% of the total measured PAHs, while Benzo[b+j] fluoranthene (Bb+jF) was the most dominant species. PAHs were mainly (80%) associated with PM2.5 size fraction. The hopane and sterane tracers also confirmed the contribution from petroleum sources (vehicles and refineries).
Remote sources and local sources both contributed to the carbonaceous aerosols observed at the site, depending on the wind speed and direction. Two pollution episodes were observed during the sampling period that provided additional insight into the transport mechanisms and potential sources of these organic pollutants. The PMF model and diagnostic ratios/indices all suggested that vehicular emissions were the primary pollution sources. In descending order of importance, PMF-derived organic sources were fugitive dust and gas-phase fugitive emissions (32.9%), gasoline engine emissions (26.7%), diesel engine emissions (20.1%), petrogenic/biogenic emissions (12.9%) and waste burning (7.4%). Because of site’s location relative to the city, local vehicular and fugitive emissions were predominant during south-easterly winds from urban areas, while long-distance petrogenic/biogenic emissions were particularly significant under prevailing north-westerly strong-wind conditions.
This first report regarding the compositional profile of carbonaceous aerosols and their sources in Doha provides information that can be used to monitor trends over time, identify primary sources of pollutants, evaluate health and environmental consequences and finally initiate pollution mitigation strategies.