Physical–chemical characterisation of the particulate matter inside two road tunnels in the São Paulo Metropolitan Area

Abstract

Abstract. The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in particulate matter vehicular emission profiles. In an effort to better characterise the emitted particulate matter, measurements of aerosol physical and chemical properties were undertaken inside two tunnels located in the São Paulo Metropolitan Area (SPMA). The tunnels show very distinct fleet profiles: in the Jânio Quadros (JQ) tunnel, the vast majority of the circulating fleet are light duty vehicles (LDVs), fuelled on average with the same amount of ethanol as gasoline. In the Rodoanel (RA) tunnel, the particulate emission is dominated by heavy duty vehicles (HDVs) fuelled with diesel (5 % biodiesel). In the JQ tunnel, PM 2.5 concentration was on average 52 µg m −3 , with the largest contribution of organic mass (OM, 42 %), followed by elemental carbon (EC, 17 %) and crustal elements (13 %). Sulphate accounted for 7 % of PM 2.5 and the sum of other trace elements was 10 %. In the RA tunnel, PM 2.5 was on average 233 µg m −3 , mostly composed of EC (52 %) and OM (39 %). Sulphate, crustal and the trace elements showed a minor contribution with 5 %, 1 %, and 1 %, respectively. The average OC : EC ratio in the JQ tunnel was 1.59 ± 0.09, indicating an important contribution of EC despite the high ethanol fraction in the fuel composition. In the RA tunnel, the OC : EC ratio was 0.49 ± 0.12, consistent with previous measurements of diesel-fuelled HDVs. Besides bulk carbonaceous aerosol measurement, polycyclic aromatic hydrocarbons (PAHs) were quantified. The sum of the PAHs concentration was 56 ± 5 ng m −3 and 45 ± 9 ng m −3 in the RA and JQ tunnel, respectively. In the JQ tunnel, benzo(a)pyrene (BaP) ranged from 0.9 to 6.7 ng m −3 (0.02-0. 1 ‰ of PM 2.5 ) whereas in the RA tunnel BaP ranged from 0.9 to 4.9 ng m −3 (0.004-0. 02 ‰ of PM 2.5 ), indicating an important relative contribution of LDVs emission to atmospheric BaP.Real-time measurements performed in both tunnels provided aerosol size distributions and optical properties. The average particle count yielded 73 000 cm −3 in the JQ tunnel and 366 000 cm −3 in the RA tunnel, with an average diameter of 48 nm in the former and 39 nm in the latter. Aerosol single scattering albedo, calculated from scattering and absorption observations in the JQ tunnel, indicates a value of 0.5 associated with LDVs. Such single scattering albedo is 20-50 % higher than observed in previous tunnel studies, possibly as a result of the large biofuel usage. Given the exceedingly high equivalent black carbon loadings in the RA tunnel, real time light absorption measurements were possible only in the JQ tunnel. Nevertheless, using EC measured from the filters, a single scattering albedo of 0.31 for the RA tunnel has been estimated. The results presented here characterise particulate matter emitted from nearly 1 million vehicles fuelled with a considerable amount of...

Particulate pollutants in the Brazilian city of São Paulo: 1-year investigation for the chemical composition and source apportionment

“…BbF was also the most abundant PAH in the 2013 intensive campaign (Pereira et al, 2017). This species was also among the most abundant PAHs in the study performed at the Jânio Quadros (JQ) tunnel, with a predominance of LDVs (Brito et al, 2013). Correlations were strong between all PAHs heavier than Flt (R > 0.8), suggesting different sources of the PAHs with lower molecular weight at this site.…”

“…It reached the mean values of 5.5, 7.6 and 12.5 ng m −3 in Int 2.5 , Ext 2.5 and Ext 10 , respectively. In the tunnels, its presence was associated with the higher contribution of LDV emissions (Brito et al, 2013). Among the nitro-PAHs with highest concentrations were 2-NFlu and 2-NBP.…”

Comparison of Two Receptor Model Techniques for the Size Fractionated Particulate Matter Source Apportionment

“…This factor appeared to represent vehicular emission (Kothai et al, 2008). As mentioned by Brito et al (2013) a significant fraction of sulphur is either emitted directly from the tailpipes or quickly oxidized to the particle phase and the study further states, sulphur as one of the most abundant trace element emitted by vehicular sources. Specially, PM emitted by diesel fueled vehicles emit soot formed during combustion, heavy hydro carbons condensed or adsorbed on the soot and sulphates (Bhandarkar, 2013).…”

Gas-Phase Polycyclic Aromatic Hydrocarbons in the Parking Lot Impacted by Light-Duty Vehicles Burning Gasoline and Ethanol Blends

“…[19][20][21][22] Results from studies conducted in Brazil in environments with characterized sources were performed in road tunnels in the city of São Paulo. 5,12 However, they reported PAHs in particulate phase, which does not enable DR comparison. In addition, comparisons using results obtained in different countries are not recommended due to the difference in the composition of combustible mixtures.…”

“…These studies presented results on particulate phase PAHs, which characterize emissions arising from the use of diesel/biodiesel and fuel mixtures in Brazil. 5,[8][9][10][11][12] However, the characterization of PAH concentrations on the vapor phase of ethanol-gasoline blends from light-duty vehicles in real operation conditions is scarce both in Brazil and in the world.…”