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Background: Primary (POA) and secondary (SOA) organic aerosols, deriving from both anthropogenic and biogenic sources, represent a major fraction of ambient particulate matter (PM) and play an important role in the etiology of respiratory and cardiovascular diseases, largely through systemic inflammation and cellular oxidative stress. The relative contributions of these species to the inhalation burden, however, are rather poorly characterized. In this study, we measured the in vitro oxidative stress response of alveolar macrophages exposed to primary and secondary PM derived from both anthropogenic and biogenic sources. Methods: POA and SOA were generated within an oxidation flow reactor (OFR) fed by pure, aerosolized α-pinene or gasoline engine exhaust, as representative emissions of biogenic and anthropogenic sources, respectively. The OFR utilized an ultraviolet (UV) lamp to achieve an equivalent atmospheric aging process of several days. Results: Anthropogenic SOA produced the greatest oxidative response (1900 ± 255 µg-Zymosan/mg-PM), followed by biogenic (α-pinene) SOA (1321 ± 542 µg-Zymosan/mg-PM), while anthropogenic POA produced the smallest response (51.4 ± 64.3 µg-Zymosan/mg-PM). Conclusions: These findings emphasize the importance of monitoring and controlling anthropogenic emissions in the urban atmosphere, while also taking into consideration spatial and seasonal differences in SOA composition. Local concentrations of biogenic and anthropogenic species contributing to the oxidative potential of ambient PM may vary widely, depending on the given region and time of year, due to factors such as surrounding vegetation, proximity to urban areas, and hours of daylight., Competing Interests: No competing interests were disclosed.

To assess particle oxidative potential in the greater Beirut area, size-resolved PM10-2.5, PM2.5-0.25 and PM0.25 samples were collected at near-freeway and urban background sites. Metals and trace elements, including Mn, Cr, Cu, Ba, Mo and Sb, displayed increased levels and crustal enrichment factors at the roadway, indicating their vehicular origin. These elements in addition to Co, V, Ni and Zn were mostly distributed in PM2.5-0.25 and PM0.25 at both sites, with moderate-to-high water-solubility (>30%). The presence of these metals, mainly air toxics, in small size ranges constitutes an added health risk. Of particular concern are elements with strong correlations (R ≥ 0.70) with reactive oxygen species (ROS)-activity, measured by a cellular assay. In PM10-2.5, road dust component Mn and soil-related element Co were highly correlated with ROS-activity. In PM2.5-0.25, vehicular abrasion element Cu and soil-derived component Co were highly associated with ROS-activity. In PM0.25, V and Ni, originating from fuel oil combustion, strongly correlated with ROS formation. ROS-activity displayed a particle-size dependency, with lowest activity associated with PM10-2.5. On a per air volume basis, size-resolved ROS-activity was 1.5-2.8 times greater at the roadside than background location, indicating that exposure to redox-active species may be greatest near the freeway. Size-fractionated PM intrinsic activity (i.e. PM mass-normalized) was comparable at both sites, possibly suggesting a similarity in the sources of ROS-active species. Relative to other urban settings, while the intrinsic redox activity of PM10-2.5 in Beirut is comparable to that measured at an urban site in Los Angeles (LA), its PM0.25-induced ROS-activity is ~2.3-fold greater. Moreover, the intrinsic ROS-activity of ambient PM2.5 in Beirut is comparable to that reported in Milan-Italy, but 3.1-times PM2.5 activity in the heavily-polluted Lahore-Pakistan. Lastly, findings suggest a dominant role of transition metals in generating ROS compared to organic carbon in the LA area., (© 2013.)

Atmospheric concentrations of PM2.5 and PM10 were measured in Beirut, Lebanon, for a period of 12 months. The daily average concentrations of PM10 and PM2.5 were found to be 51.3 ± 33.1 and 30.3 ± 9.4 µg.m-3, respectively, with corresponding maximum values of 359.7 and 208.6 µg.m-3. The annual average concentrations of PM10 and PM2.5 exceeded the World Health Organization's standards by 150% and 200%, respectively. The mean concentration of coarse particles (PM10-2.5) was found to be 41% of the average PM10, suggesting that the site was also influenced by re-suspended surface dust and soil. The mean PM2.5/PM10 ratio for the entire study period was 0.61 ± 0.12. This indicates that in Beirut, PM2.5 accounts for about 61% of PM10. Such a large fraction of fine particles could have considerable effect on health; thus, it is necessary to quantify its impact. Daily concentrations of PM10 and PM2.5 exceeded the upper threshold limit on 133 and 129 days, respectively, representing 39% and 38% of the entire sample, respectively. These findings indicate the important role dust events play within this area. Concentrations of PM2.5 were highly correlated with NO2, whereas concentrations of PM10 and PM10-2.5 were not associated with any gaseous pollutant. Regression analysis showed that 93% of PM2.5 and 43% of PM10 particle mass concentrations were derived from road traffic exhaust in Beirut. [ABSTRACT FROM AUTHOR]

In this study, we examine the oxidative potential of airborne particulate matter (PM) in Beirut, Lebanon, as influenced by dust events originating in the Sahara and Arabian deserts. Segregated fine (<2.5 μm) and coarse (2.5–10 μm) PM samples collected during dust events, as well as during non-dust periods, were analyzed for chemical composition, and the in vitro alveolar macrophage (AM) assay was utilized to determine the oxidative potential of both types of samples. We performed Spearman rank-order correlation analysis between individual chemical components and the oxidative potential of PM to examine the impact of the changes in PM chemical composition due to the occurrence of dust events on overall PM oxidative potential. Our findings revealed that the oxidative potential of Beirut's urban PM during non-dust periods was much higher than during dust episodes for fine PM. Our findings also indicated that tracers of tailpipe emissions (i.e., elemental (EC) and organic carbon (OC)), non-tailpipe emissions (i.e., heavy metals including Cu, Zn, As, Cd, and Pb), and secondary organic aerosols (SOA) (i.e., water-soluble organic carbon, WSOC) were significantly associated with the oxidative potential of PM during dust days and non-dust periods. However, the contribution of desert dust aerosols to Beirut's indigenous PM composition did not exacerbate its oxidative potential, as indicated by the negative correlations between the oxidative potential of PM and the concentrations of crustal elements that were enriched during the dust days. This suggests that aerosols generated during Saharan and Arabian dust events pose no additional health risk to the population due to PM-triggered reactive oxygen species formation. These results significantly contribute to our understanding of the effects of desert dust aerosols on the composition and oxidative potential of PM in several countries throughout the entire Middle East region that are impacted by dust events in the Sahara and Arabian deserts. [ABSTRACT FROM AUTHOR]