Vehicle fleet emissions of black carbon, polycyclic aromatic hydrocarbons, and other pollutants measured by a mobile laboratory in Mexico City

Abstract

Abstract. Black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) are of concern due to their effects on climate and health. The main goal of this research is to provide the first estimate of emissions of BC and particle-phase PAHs (PPAHs) from motor vehicles in Mexico City. The emissions of other pollutants including carbon monoxide (CO), oxides of nitrogen (NO x ), volatile organic compounds (VOCs), and particulate matter of diameter 2.5 µm and less (PM 2.5 ) are also estimated. As a part of the Mexico City Metropolitan Area field campaign in April 2003 (MCMA-2003, a mobile laboratory was driven throughout the city. The laboratory was equipped with a comprehensive suite of gas and particle analyzers, including an aethalometer that measured BC and a photoionization aerosol sensor that measured PPAHs. While driving through traffic, the mobile lab continuously sampled exhaust plumes from the vehicles around it. We have developed a method of automatically identifying exhaust plumes, which are then used as the basis for calculation of fleet-average emissions. In the approximately 75 h of on-road sampling during the field campaign, we have identified ∼30 000 exhaust measurement points that represent a variety of vehicle types and driving conditions. The large sample provides a basis for estimating fleet-average emission factors and thus the emission inventory. Motor vehicles in the Mexico City area are estimated to emit 1700±200 metric tons BC, 57±6 tons PPAHs, 1 190 000±40 000 tons CO, 120 000±3000 tons NO x , 240 000±50 000 tons VOCs, andCorrespondence to: L. C. Marr (lmarr@vt.edu) 4400±400 tons PM 2.5 per year, not including cold start emissions. The estimates for CO, NO x , and PPAHs may be low by up to 10% due to the slower response time of analyzers used to measure these species. Compared to the government's official motor vehicle emission inventory for the year 2002, the estimates for CO, NO x , VOCs, and PM 2.5 are 38% lower, 23% lower, 27% higher, and 25% higher, respectively. The distributions of emission factors of BC, PPAHs, and PM 2.5 are highly skewed, i.e. asymmetric, while those for benzene, measured as a surrogate for total VOCs, and NO x are less skewed. As a result, the total emissions of BC, PPAHs, and PM 2.5 could be reduced by approximately 50% if the highest 20% of data points were removed, but "super polluters" are less influential on overall NO x and VOC emissions.

Global anthropogenic emissions of particulate matter including black carbon

“…for Euro 1 to 6, were developed based on existing studies mainly from the United States (Ban-Weiss et al, 2009;Durbin et al, 1999;Hsu and Mullen, 2007;Yanowitz et al, 2000) and Europe (Carslaw et al, 2011;Ekström et al, 2004), studying the 90-95th percentile as the cut-off between high and normal emitting behaviour. Similar datasets from Australia (Smit and Bluett, 2011), China (Guo et al, 2007), Thailand (Subramanian et al, 2009), and Mexico City (Jiang et al, 2005) were also studied in order to find which percentiles would represent the local fleets if the amplification factors identified, based on the 90-95th percentiles in the European and US studies, were also applied there. The identified percentiles then determined what share of the vehicle fleet corresponded to the amplification factors specified for the highemitting vehicles.…”

Air quality in North America's most populous city – overview of the MCMA-2003 campaign

“…Most importantly the mean emissions ratios for nitrogen dioxide, formaldehyde, benzene and toluene measured by open path methods at CENICA agreed surprisingly well with the integrated distributions of nearby on-road exhaust plume measurements made with the ARI mobile laboratory. Figure 3 shows mobile emissions estimated from measured on-road emission indices by the ARI mobile laboratory on a wide range of MCMA roadways for NO x from light-duty gasoline vehicles , and CO and VOC from the full on-road fleet (Jiang et al, 2005), although without distinction of the corresponding type of vehicle and are more likely to represent aggregated emission factors of everything on the road (diesel, gasoline, LPG, CNG) plus some non-road emissions. Figure 3 also shows estimated on-road fleet SO 2 emissions determined from SO 2 /CO 2 concentration growth measurements obtained by long open-path absorption at CENICA .…”

“…Peak concentrations of PAHs were reached during the morning rush hour and were of the order of 120 ng m −3 , which is higher than in US cities . Motor vehicles were found to be a significant source of PAHs, with 20% of the vehicles accounting for 50% of the emissions (Jiang et al, 2005), while garbage and biomass burning were also sources of these species. Photoelectric measurements (PAS) detect a very rapid decay of surface PAHs in the morning photochemistry, which may be due to surface reactions of the PAHs and/or to coating of the particles with secondary species that reduce the response of the instrument Baumgardner et al, 2006).…”

Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry

“…The most recent and detailed studies of aerosols in Mexico City were carried out during the MCMA-2003 campaign Dunn et al, 2004;Jimenez et al, 2004;Jiang et al, 2005;Marr et al, 2006;. Electron microscopy was used to infer the mixing state and transformation of soot particles (Johnson et al, 2005).…”