T. Castro

Measurements of Mexico City nanoparticle size distributions: Observations of new particle formation and growth

Received 13 January 2004; revised 5 March 2004; accepted 30 April 2004; published 22 May 2004. [1] Continuous measurements of the size distribution of atmospheric aerosol in the 3–48 nm diameter range were performed in the Mexico City metropolitan area. These measurements were made during the period 10–20 April 2003 at a ground-based, mountain pass site in the southeast corner of the Mexico City Federal District and during the period 2–11 May 2003 at the CENICA site located near the city center. The objectives of this work were to determine the frequency of new particle formation and to characterize the atmospheric chemical and meteorological conditions that lead to these events. Several new particle formation events were recorded during the study. Events observed in the mountain pass correlate with northerly winds and elevated levels of sulfur dioxide in the mid-morning while events observed in the city correlate with elevated concentrations of sulfur dioxide and low particulate matter mass concentrations in the afternoon hours. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere— composition and chemistry. Citation: Dunn, M. J., J.-L.

Mexico City air quality: a qualitative review of gas and aerosol measurements (1960-2000)

Mexico City, one of the largest cities in the world, has a major problem with high levels of anthropogenic gases and aerosols. Some facets of this problem have been studied through measurements made during the past 40 years. These measurements are reviewed and evaluated with respect to physical processes that underlie the primary and secondary formation of gases and aerosols, their spatial and temporal evolution as well as their potential impact on the local and regional environment. Past measurements are heavily biased towards certain locations and time periods, and are of limited use for understanding fundamental processes that govern the formation and evolution of the principal pollutants. Recommendations are made whereby the measurement database could be expanded to better represent the characteristics of Mexico City gases and aerosols and to contribute to mitigation strategies that would lessen the environmental impact of these pollutants. # 2001 Elsevier Science Ltd. All rights reserved.

Sensitivity analysis of a UV radiation transfer model and experimental photolysis rates of NO2 in the atmosphere of Mexico City

Abstract Photolysis of key species such as nitrogen dioxide, ozone and aldehydes, are the elementary reactions leading to the formation of photochemical smog. Calculations and experimental measurements (in particular, nitrogen dioxide) of these key reactions are reported, as well as, the sensitivity of them to the ozone column, local albedo and properties of the urban aerosol layer in Mexico City. A radiation transfer model (RTM ), based on the delta-Eddington approximation, was used in the calculations. The results show the importance of providing local resolution for photolysis rates by considering different local conditions within the modeling domain of air quality models.

Study of the regional air quality south of Mexico City (Morelos state)

Results from the first study of the regional air quality in Morelos state (located south of Mexico City) are presented. Criteria pollutants concentrations were measured at several sites within Morelos in February and March of 2007 and 2009; meteorological data was also collected along the state for the same time periods; additionally, a coupled meteorology-chemistry model (Mesoscale Climate Chemistry Model, MCCM) was used to gain understanding on the atmospheric processes occurring in the region. In general, concentrations of almost all the monitored pollutants (O(3), NO(x), CO, SO(2), PM) remained below the Mexican air quality standards during the campaign; however, relatively high concentrations of ozone (8-hour average concentrations above the 60 ppb level several times during the campaigns, i.e. exceeding the World Health Organization and the European Union maximum levels) were observed even at sites with very low reported local emissions. In fact, there is evidence that a large percentage of Morelos vegetation was probably exposed to unhealthy ozone levels (estimated AOT40 levels above the 3 ppm h critical limit). The MCCM qualitatively reproduced ozone daily variations in the sites with an urban component; though it consistently overestimated the ozone concentration in all the sites in Morelos. This is probably because the lack of an updated and detailed emission inventory for the state. The main wind patterns in the region corresponded to the mountain-valley system (downslope flows at night and during the first hours of the day, and upslope flows in the afternoon). At times, Morelos was affected by emissions from surrounding states (Distrito Federal or Puebla). The results are indicative of an efficient transport of ozone and its precursors at a regional level. They also suggest that the state is divided in two atmospheric basins by the Sierras de Tepoztlán, Texcal and Monte Negro.

Least squares variational approach to the convective mixing height estimation problem

Abstract A least squares variational approach is suggested to estimate the atmospheric mixed layer depth (or mixing height ) under convective conditions from the vertical profile of virtual potential temperature. This method was implemented as a software application that could be a very useful tool to estimate the mixing height parameter required in air pollution modeling studies. The software was used to estimate Mexico City mixing heights from the atmospheric sounding data between January to May of 1993 and 1994, and the monthly statistics evolution of the 11:00z and 23:00z mixing height values is presented for this period. The estimations produced by this method for the afternoon mixing height were found in a good agreement with the daily maximum value calculated with the dry adiabatic temperature method.

Photolytic rates for NO2, O3 and HCHO in the atmosphere of Mexico City

Abstract We report theoretical calculations of photolysis rates for NO 2 , O 3 and HCHO in the atmosphere of Mexico City. To estimate the radiance needed in the calculations, the equation of transfer is solved by the delta-Eddington method. An atmosphere of air, NO 2 , O 3 and dry aerosols is modeled.

Main Characteristics of Mexico City Local Wind Events during the MILAGRO 2006 Campaign within a Meso-β Scale Lattice Wind Modeling Approach

A characterization of local wind events in Mexico City, which occurred during MILAGRO campaign, was carried out within the framework of a lattice wind modeling approach at a meso-β scale. Mexico City was modeled as a 2D lattice domain with a given number of identical cells. Local wind conditions at any cell were described by a state variable defined by the spatial averages of wind attributes such as speed, direction, divergence, and vorticity. Full and partial densities of wind states were discussed under different conditions using two simple lattice wind models. We focus on the results obtained with the 1-cell lattice wind model and provide brief comments about preliminary results obtained with the 4-cell model. The 1-cell model allowed identifying the main patterns of the wind circulation in Mexico City throughout the study period (anabatic and katabatic winds, winds induced by the urban heat island, and winds with high possibilities for exchanging pollutants between Mexico City and the neighboring settlements, among others). The model showed that Mexico City wind divergence and vorticity disclose superposed oscillations whose most important periods were 24 and 12 hours, suggesting strong connections with the diurnal cycle of incoming solar radiation and the urban heat island.

Spatial variability of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the southern Gulf of Mexico

Environmental context Dimethylsulfide (DMS), the main biogenic sulfur compound in the atmosphere, is produced by the marine biosphere and plays an important role in the atmospheric sulfur cycle. This study recorded the spatial variability of DMS and dissolved and particulate dimethylsulfoniopropionate (DMSP) in the water column of the southern Gulf of Mexico. The results suggest that the spatial variability of DMS and DMSP is directly related to the hydrodynamics of the study area. Abstract The spatial variability of dimethylsulfide (DMS) and dissolved and particulate dimethylsulfoniopropionate (DMSPd and DMSPp) was recorded in the southern Gulf of Mexico at three different depths (10, 30 and 60m) in January 2013. DMS and DMSP values were recorded through solid-phase microextraction coupled to gas chromatography. Average concentrations of DMS (2.8±1.5nM), DMSPd (1.7±0.9nM) and DMSPp (352±157nM) were significantly correlated with chlorophyll-a concentrations and the depth of the mixed layer. Vertical concentration profiles were similar, indicating a well-mixed water column with a thermocline at a depth of 50–100m. Average DMS sea-to-air flux was 5.0±1.7µmolm–2day–1. The greatest fluxes were recorded at the stations in the western region of the study area, owing to the combined effect of high DMS concentrations (3.7–7.21nM) and a high wind speed (4.4–6.8ms–1). The greatest concentrations were recorded at the stations nearest the coast. The distribution of DMS and DMSP was apparently related to the oceanic hydrodynamics.

Do we need an Ad hoc chemical mechanism for Mexico City's photochemical smog?

Chemical mechanisms in mathematical models for air quality studies represent the synthesis of about 30 years of research in gas kinetics and atmospheric chemistry, and are able to represent, to a good extent, the chemistry of photochemical smog. However, due to the large amount of computer resources required by these models, different well-known approaches have been used in order to make them operative. In any of these approaches, a set of educated guesses is made, based upon the knowledge of the conditions under which the reactions occur and the competition between them, and upon the expected absolute and relative concentrations of the emitted reactive organic gases (ROG)

Photolysis Of Nitrogen Dioxide And Ozone InThe Atmosphere Of Mexico City

We report theoretical photolysis rates for the nitrogen dioxide and ozone in the atmosphere of Mexico City. To estimate the spectral irradiance needed in the calculations, the equation of transfer is solved by the delta-Eddington method. An atmosphere of air, nitrogen dioxide, ozone and dry aerosol is modeled. INTRODUCTION A state-of-the art photochemical kinetics model requires the specification of time-dependant rates for the two most important photolytic reactions: NO + hy > NO + 0 (1) 0 + hv > 0 + 0(*D) (2) Transactions on Ecology and the Environment vol 1,