Luisa T. Molina

UV absorption cross sections of HO2NO2 vapor

Abstract The UV absorption cross sections for gas phase pernitric acid (HO 2 NO 2 ) were measured between 190 and 330 nm at 298 K and 1 atm total pressure. The HO 2 NO 2 vapor was prepared in a flowing stream of nitrogen in the presence of H 2 O, H 2 O 2 , HNO 3 and NO 2 . The composition of the mixture was established by visible and IR absorption spectroscopy and by chemical titration after absorption in aqueous solutions. The HO 2 NO 2 cross sections ranged from approximately 10 −17 cm 2 molecule −1 at 190 nm to about 10 −21 cm 2 molecule −1 at 330 nm. The experimental uncertainty (one standard deviation) ranged from 5% at 200 nm to 30% at 330 nm and fell mainly in the 10% range. The solar photodissociation rate in the troposphere and lower stratosphere was estimated to be about 10 −5 s −1 for a solar zenith angle of 0°.

The rate constant for the reaction of O/3P/ atoms with ClONO2

Abstract The O( p3 P) + ClONO 2 reaction has been studied in a fast flow system over the temperature range from 213 to 295 K, using the air-afterglow technique for the detection of oxygen atoms under pseudo first order conditions. A value of (3.4± 0.6) × 10 −12 exp[(−840 ± 60)/ T ] cm 3 molecule −1 s −1 has been obtained for the rate constant.

Remote Sensing of Glyoxal by Differential Optical Absorption Spectroscopy (DOAS): Advancements in Simulation Chamber and Field Experiments

Air pollution in many large cities is linked with the photochemical transformation of primary pollutants like VOCs (volatile organic compounds) and NOx, which in the presence of sunlight foster the formation of secondary pollutants including ozone (O3) and secondary organic aerosol (SOA) (Finlayson-Pitts and Pitts 2000; Molina and Molina 2002). ‘Photochemical smog’ has adverse effects on human health (Kunzli et al. 2000; Evans et al. 2002), the ecosystem (Middleton et al. 1950; Gregg et al. 2003) and regional climate (Lelieveld et al. 2001; Ramanathan and Crutzen 2003).

Impacts of using an ensemble Kalman filter on air quality simulations along the California-Mexico border region during Cal-Mex 2010 field campaign.

The purpose of this study is to investigate the impact of using an ensemble Kalman filter (EnKF) on air quality simulations in the California-Mexico border region on two days (May 30 and June 04, 2010) during Cal-Mex 2010. The uncertainties in ozone (O3) and aerosol simulations in the border area due to the meteorological initial uncertainties were examined through ensemble simulations. The ensemble spread of surface O3 averaged over the coastal region was less than 10ppb. The spreads in the nitrate and ammonium aerosols are substantial on both days, mostly caused by the large uncertainties in the surface temperature and humidity simulations. In general, the forecast initialized with the EnKF analysis (EnKF) improved the simulation of meteorological fields to some degree in the border region compared to the reference forecast initialized with NCEP analysis data (FCST) and the simulation with observation nudging (FDDA), which in turn leading to reasonable air quality simulations. The simulated surface O3 distributions by EnKF were consistently better than FCST and FDDA on both days. EnKF usually produced more reasonable simulations of nitrate and ammonium aerosols compared to the observations, but still have difficulties in improving the simulations of organic and sulfate aerosols. However, discrepancies between the EnKF simulations and the measurements were still considerably large, particularly for sulfate and organic aerosols, indicating that there are still ample rooms for improvement in the present data assimilation and/or the modeling systems.

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

This study investigates the effects of using the US-EPA MOVES2010a model for estimating PM2.5 emission factors in the Mexican vehicle fleet; the results are compared with the current PM2.5 emissions estimates in the 2005 Mexican National Emissions Inventory (MNEI). Our results show that model-based PM2.5 emissions factors updated from recent studies can have significant impacts on the estimated PM2.5 emissions from mobile sources in Mexico. Higher fractions of older vehicles tend to increase PM2.5 emissions estimates using MOVES2010a with respect to the 2005 MNEI estimates; however, the overall impact on PM emissions varies depending on the vehicle population and vehicle age composition for each Mexican state fleet. These effects are primarily driven by the higher PM2.5 emission factors from the gasoline-powered vehicles and by the high fractions of older gasoline and diesel vehicles. The results also indicate that the estimated MOVES2010a PM2.5 emission factors for Mexico were particularly sensitive to vehicle speed, ambient temperature and sulfur content, but not the relative humidity. There is a strong need to better understand the characteristics of fine particulate matter (PM) emitted from gasoline and diesel-powered vehicles in major urban areas in Mexico.

Determination of particulate lead during MILAGRO/MCMA-2006 using Aerosol Mass Spectrometry

D. Salcedo, T. B. Onasch, A. C. Aiken, L. R. Williams, B. de Foy, M. J. Cubison, D. R. Worsnop, L. T. Molina, and J. L. Jimenez Centro de Investigaciones Quı́micas, Universidad Autónoma del Estado de Morelos, Cuernavaca, México Center for Aerosol and Cloud Chemistry, Aerodyne Research, Billerica, MA, USA Cooperative Institute for Research in the Environmental Sciences (CIRES) and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA Department of Earth and Atmospheric Sciences, Saint Louis University, Saint Louis, MO, USA Molina Center for Energy and the Environment, La Jolla, CA, USA

Conclusions: Key Findings and Recommendations

During this past decade, the government of the Mexico City Metropolitan Area (MCMA) has made tremendous progress in improving air quality. Substantial reductions in the concentrations of criteria pollutants (such as lead, carbon monoxide, and sulfur dioxide, among others) have been secured through the development and implementation of comprehensive air quality management programs; improvements in monitoring and evaluation or air pollution; strengthening and enforcing vehicle inspection and maintenance systems; replacement of fuel oil by natural gas in industry and the power sector; specific actions to reduce volatile emission from gasoline stations and storage tanks in industry; improved specifications for transport and industrial fuels; and other measures. The closure of the 18 de Marzo oil refinery and the transition to natural gas by power plants have contributed to a major reduction in pollutants, notably sulfur dioxide. In addition, programs such as “No driving day” (Hoy No Circula) have been effective incentives to modernize the vehicle fleet and to help insure the proper maintenance of vehicles. Efforts have also been undertaken specifically to address institutional barriers and to integrate air quality concerns with transport and related issues.