Sources of PM<sub>2.5</sub> carbonaceous aerosol in Riyadh, Saudi Arabia

Abstract

Abstract. Knowledge of the sources of carbonaceous aerosol affecting air quality in Riyadh, Saudi Arabia, is limited but needed for the development of pollution control strategies. We conducted sampling of PM 2.5 from April to September 2012 at various sites in the city and used a thermo-optical semi-continuous method to quantify the organic carbon (OC) and elemental carbon (EC) concentrations. The average OC and EC concentrations were 4.7 ± 4.4 and 2.1 ± 2.5 µg m −3 , respectively, during this period. Both OC and EC concentrations had strong diurnal variations, with peaks at 06:00-08:00 LT and 20:00-22:00 LT, attributed to the combined effect of increased vehicle emissions during rush hour and the shallow boundary layer in the early morning and at night. This finding suggested a significant influence of local vehicular emissions on OC and EC. The OC / EC ratio in primary emissions was estimated to be 1.01, close to documented values for diesel emissions. Estimated primary organic carbon (POC) and secondary organic carbon (SOC) concentrations were comparable, with average concentrations of 2.0 ± 2.4 and 2.8 ± 3.4 µg m −3 , respectively.We also collected 24 h samples of PM 10 onto quartz microfiber filters and analyzed these for an array of metals by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Total OC was correlated with Ca (R 2 of 0.63), suggesting that OC precursors and Ca may have similar sources, and the possibility that they underwent similar atmospheric processing. In addition to a ubiquitous dust source, Ca is emitted during desalting processes in the numerous refineries in the region and from cement kilns, suggesting these sources may also contribute to observed OC concentrations in Riyadh. Concentration weighted trajectory (CWT) analysis showed that high OC and EC concentrations were associated with air masses arriving from the Persian Gulf and the region around Baghdad, locations with high densities of oil fields and refineries as well as a large Saudi Arabian cement plant. We further applied positive matrix factorization to the aligned dataset of EC, OC, and metal concentrations (Al, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, and V). Three factors were derived and were proposed to be associated with oil combustion, industrial emissions (Pb based), and a combined source from oil fields, cement production, and local vehicular emissions. The dominant OC and EC source was the combined source, contributing 3.9 µg m −3 (80 %) to observed OC and 1.9 µg m −3 (92 %) to observed EC.

Source Apportionment of Ambient Black Carbon during the COVID-19 Lockdown

“…The WCWT values indicated a relatively narrow distribution in the post-LD stage During the entire study period, long-range source locations with WCWT values > 1 µg/m 3 , including the central and southeastern section of Iraq, Iran's western border with Iraq, Kuwait, distributed zones in the Arabian Gulf, and the United Arab Emirates, were associated with moderate to high eBC concentrations observed at the receptor site (Figure 7a). The impacts of long-range source zones mentioned herein were also recently reported for the BC levels over Riyadh and Dammam's rainwater chemical compositions [52,83]. In addition, it is evident from Figure 7a that the effects of regional source locations, such as the Arabian Gulf coastline of the KSA, Bahrain, and Qatar, with moderate to high WCWT values on the observed eBC levels were substantial.…”

“…Their study revealed that the high BC concentrations were associated with local traffic emissions and long-range transport contributions. Bian et al [52] researched the sources of carbonaceous aerosols from April to September 2012 in Riyadh, the capital of the KSA. The mean BC concentration was 2.1 ± 2.5 µg/m 3 during their study period.…”

Evolution of organic carbon during COVID-19 lockdown period: Possible contribution of nocturnal chemistry

“…In most of these previous studies, the lowest value (5–20%) of OC/EC was used empirically ( Yao et al, 2020 ; Zhang et al, 2019a ). In this study, the appropriate value of (OC/EC) pri was determined using the MRS method ( Bian et al, 2018 ; Ji et al, 2018b ; Millet et al, 2005 ; Sun et al, 2020a ; Wu and Yu, 2016 ), which determining the (OC/EC) pri when the smallest correlation coefficient (R 2 ) between SOC and EC achieved by assuming a series of continuous OC/EC ratios. More details can be found elsewhere ( Wu et al, 2019 ; Wu and Yu, 2016 ; Yao et al, 2020 ).…”

Amplification of black carbon light absorption induced by atmospheric aging: temporal variation at seasonal and diel scales in urban Guangzhou

“…In our previous work, numerical studies were performed and the results showed that the minimum R squared method (MRS) is more robust in SOC estimation than the minimum OC/EC and percentile OC/EC method (Wu and Yu, 2016). As a result, the MRS method had been gradually adopted for SOC estimation in recent studies (Xu et al, 2018b;Bian et al, 2018;Ji et al, 2018;Ying et al, 2018;Ji et al, 2019;Wu et al, 320 2019).…”