Comparison of emissions from on-road sources using a mobile laboratory under various driving and operational sampling modes

Abstract

Abstract. Mobile sources produce a significant fraction of the total anthropogenic emissions burden in large cities and have harmful effects on air quality at multiple spatial scales. Mobile emissions are intrinsically difficult to estimate due to the large number of parameters affecting the emissions variability within and across vehicles types. The MCMA-2003 Campaign in Mexico City has showed the utility of using a mobile laboratory to sample and characterize specific classes of motor vehicles to better quantify their emissions characteristics as a function of their driving cycles. The technique clearly identifies "high emitter" vehicles via individual exhaust plumes, and also provides fleet average emission rates. We have applied this technique to Mexicali during the Border Ozone Reduction and Air Quality Improvement Program (BORAQIP) for the Mexicali-Imperial Valley in 2005. We analyze the variability of measured emission ratios for emitted NO x , CO, specific VOCs, NH 3 , and some primary fine particle components and properties by deploying a mobile laboratory in roadside stationary sampling, chase and fleet average operational sampling modes. The measurements reflect various driving modes characteristic of the urban fleets. The observed variability for all measured gases and particle emission ratios is greater for the chase and roadside stationary sampling than for fleet average measurements. The fleet Correspondence to: M. Zavala (miguelz@mce2.org) average sampling mode captured the effects of traffic conditions on the measured on-road emission ratios, allowing the use of fuel-based emission ratios to assess the validity of traditional "bottom-up" emissions inventories. Using the measured on-road emission ratios, we estimate CO and NO x mobile emissions of 175±62 and 10.4±1.3 metric tons/day, respectively, for the gasoline vehicle fleet in Mexicali. Comparisons with similar on-road emissions data from Mexico City indicated that fleet average NO emission ratios were around 20% higher in Mexicali than in Mexico City whereas HCHO and NH 3 emission ratios were higher by a factor of 2 in Mexico City than in Mexicali. Acetaldehyde emission ratios did not differ significantly whereas selected aromatics VOCs emissions were similar or smaller in Mexicali. Nitrogen oxides emissions for on-road heavy-duty diesel truck (HDDT) were measured near Austin, Texas, as well as in both Mexican cities, with NO y emission ratios in Austin < Mexico City < Mexicali.

Modeling the Dynamics of Air Pollutants: Trans-Boundary Impacts in the Mexicali-Imperial Valley Border Region

“…Overall, the gas-phase species results indicate a tendency of the model to underestimate the pollutant concentrations. This is in line with the results obtained from mobile laboratory measurements that indicate an underestimation of the official emissions inventory for Mexicali (Zavala et al, 2009). PM proved to be more difficult to simulate correctly, which is a known setback of current CTMs (Russell, 2008).…”

Analysis of model-based PM2.5 emission factors for on-road mobile sources in Mexico

“…An analysis of the data inputs used for estimating the PM2.5 emissions from mobile sources in the 2005 MNEI indicates that the average vehicle speed and temperature had the highest sensitivity on the MOVES2010a PM2.5 emission factors estimates. In general, PM2.5 emission factors were higher for higher average vehicle speeds, consistent with studies indicating higher PM emission rates observed under high engine load conditions (i.e., vehicle Table 1. speeds) (Kean et al, 2003;Cadle et al, 2007;Zavala et al, 2009b). Similarly, recent studies are consistent with the observation that fine PM emissions increase with engine load for diesel-powered engines and that volatile fraction of fine PM decreases with increasing load (Ziemmann et al, 2002;Kwon et al, 2003).…”

Aerosol effects on the photochemistry in Mexico City during MCMA-2006/MILAGRO campaign

“…Aerosols influence climate directly by scattering or absorbing a fraction of the incoming solar radiation to cool or warm the atmosphere, and indirectly via their roles as cloud condensation nuclei (CCN) and ice nuclei (IN), by modifying optical properties and lifetime of clouds (e.g., Penner et al, 2001;Zhang et al, 2007). Additionally, scattering or absorbing a fraction of solar radiation by aerosols also increase or decrease photolysis rates in the atmosphere, affecting ozone (O 3 ) formation and atmospheric oxidation capacity Li et al, 2005).…”