Mobile laboratory measurements of black carbon, polycyclic aromatic hydrocarbons and other vehicle emissions 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 (NOx), volatile organic compounds (VOCs), and particulate matter of diameter 2.5 µm and less (PM2.5) 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 is continuously sampling 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 emission factors. 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 NOx, 202 000±4000 tons VOCs, and 4400±400 tons PM2.5 per year, not including cold start emissions. The estimates for CO, NOx, 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, NOx, VOCs, and PM2.5 are 38% lower, 23% lower, 7% higher, and 26% higher, respectively. The distributions of emission factors of BC, PPAHs, and PM2.5 are highly skewed, i.e. asymmetric, while those for benzene, measured as a surrogate for total VOCs, and NOx are less skewed. As a result, the total emissions of BC, PPAHs, and PM2.5 could be reduced by approximately 50% if the highest 20% of data points were removed, but ''super polluters'' are less influential on overall NOx and VOC emissions.

Spatial and temporal variability of particulate polycyclic aromatic hydrocarbons in Mexico City

“…The mass ratio of particulate SPAH/NO x measured along roads during the MCMA-2003 field campaign was 4.7±5.9×10 −4 (Jiang et al, 2005). During the MCMA-2006 field campaign, this ratio was 1.09±0.05 ng m −3 ppb −1 , or 7.7±0.4×10 −4 in mass terms, at T0 (and similar at the other urbanized sites T1 and PEMEX).…”

Technical note: Evaluation of standard ultraviolet absorption ozone monitors in a polluted urban environment

“…Almost all of these events were observed when the ARI Mobile Lab was clearly sampling the exhaust from a diesel vehicle Herndon et al, 2005;Shorter et al, 2005); the rest of the events were from indeterminate sources. Of the various instruments on board the ARI Mobile Lab, the best correlations in time for these interferences were found with several particle instruments, specifically a DustTrak PM 2.5 instrument (TSI Model 8520), which measured the mass loading of particulate matter smaller than 2.5 microns, an EcoChem Polycyclic Aromatic Hydrocarbon (PAH) monitor (PAS 2000 CE), which measured signal response to photoionization of particulate surfaces and has been shown to respond strongly to surface bound PAHs and possibly to elemental carbon (EC), and an EcoChem Diffusion Charger monitor (DC 2000 CE), which measures particulate active surface area; see Marr et al (2004) and Jiang et al (2005) for a description of the use and interpretation of these instruments while sampling very fresh on-road exhaust emissions. Also on board the ARI Mobile Lab, an Aerodyne Aerosol Mass Spectrometer (AMS) (Jayne et al, 2000) measured size resolved chemical composition of non-refractory particles less than 1 µm.…”

Correlations of Ambient Temperature and Relative Humidity with Submicron Particle Number Concentration Size Distributions in On-Road Vehicle Plumes

“…The general measurement strategies used by mobile laboratories are well described by Kolb et al (2004) and Jiang et al (2005). In addition, Jiang et al (2005) proposed that the mobile data could be analyzed using microscopic (for an individual vehicle) and macroscopic (for a larger number of vehicles) approaches.…”

“…(2) How to isolate the influence of T on on-road vehicular particle concentration from that of RH? Several groups have developed mobile laboratories for real-time measurements to characterize gas and particulate pollutants in the atmosphere (Bukowiecki, et al 2002;Seakins et al 2002;Vogt et al 2003;Kittelson et al 2004;Kolb et al 2004;Jiang et al 2005). Mobile measurements provide "continuous snapshots" of the air quality.…”