Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Methane emission factors from different cattle manure management systems including simulated slurry system fermentation were experimentally determined in this and a previous study (González-Avalos and Ruiz-Suárez, 2001). Combining results from both studies, we report values for maximum CH4 yield, called B0, for manure produced by cattle under different production systems and climates, which also implies different quality of feeds and associated methane conversion factors (MCF) for distinct manure management systems. This set of data has the same functionality than that of the current IPCC methodology, but offer a wider set of key parameters to estimate methane emissions from manure, which may be of interest in other countries. In this work, we report MCF can be up to 17.3 times smaller than those suggested in the 1996 Revised IPCC Methodology Guidelines (IPCC, 1997) and Good Practice Guidance (IPCC, 2000).  

In urban areas high air pollutant concentrations may be observed, mostly within street canyons, where buildings and other obstacles disturb the airflow and turbulence. Air motions inside the street canyons are influenced by aerodynamic and thermal effects and by the movements of the vehicles. In this article, we analyze hourly CO and NOx concentrations measured at 1.5 m height on the west side of a street canyon of Göttinger Strasse in Hannover (Germany) and background CO and NOx, wind speed and direction that have been measured on the roof of a nearby building. Information of traffic flow in the street is also available. Results show the presence of a vortex cell inside the street canyon when the ambient wind is greater than 1.8 m/s and is mainly perpendicular to the street axis. We evaluated of the relative influence of ambient and traffic-induced turbulences on local concentrations inside the canyon. The results show that traffic-induced turbulence becomes important when the wind is lower than 2 m/s.

Variations of solar irradiance (total and spectral) are quantities purported to have an influence on climate. The aim of this paper is to reconstruct the total solar irradiance from 1832 to the present. The contributions of active regions and the quiet sun are modelled separately using the method developed by Solanki and Fligge (1999). The areas of sunspots observed since 1832 are used to compute the contribution of active regions to the irradiance changes.

In many cities, the main tool used to assess pollution abatement policies is the air quality information obtain-ed from local monitoring network. However, in the context of a complex meteorology and land use such as those prevailing in México City, the point-wise character and lack of detailed chemistry of this information may confer conflictive or biased information. The approach to understand the problem could be not based on solid ground. It is not until the measurement effort is complemented with detailed meteorological and air quality modeling that proper use of the information can be assured. In order to provide an example of this assertion, the usefulness of measured air quality data is gauged in a simplified manner, constructing three dimensional graphs containing local emission concentrations of nitrogen oxides (NOx), volatile organic compounds (VOC) and maximum ozone (O3) concentrations, that we call “ozone isopleths”, for three sites in México City. Together with corresponding wind rose data, an interpretation of the air pollution transport in the Valley of México using only measured data is attempted. This interpretation, based on measured information subject to local influences, is compared with recent air quality modeling results showing that when measured data is used in conjunction with air quality modeling a better interpretation of air pollution problem can be obtained. A correct strategy to study the air quality problem, especially in the case of México City where complex meteorology and land use is present, should be that both endeavors, measuring and modeling, are pursued with equal vigor.  

Both the enhancement of the aerosol number concentration and the relative dispersion of the cloud droplet size distribution (spectral dispersion) on a regional scale can modify the cloud reflectivity. This work is focused on the role that pre-cloud aerosol plays in cloud reflectivity. Log-normal aerosol size distributions were used to describe two aerosol types: marine and rural. The number of aerosols that activate to droplets was obtained based on Abdul-Razzak and Ghan’s (2000) activation parameterization. The cloud albedo taking into account the spectral dispersion effect in the parameterization of cloud effective radius and in the scattering asymmetry factor has been estimated. Two different scaling factors to account for dispersion were used. The sensitivity of cloud albedo to spectral dispersion-cloud droplet number concentration relationship in connection to the changes in liquid water content (LWC), and the cloud droplet effective radius has been also investigated. We obtained higher values of effective radius when dispersion is taken into account, with respect to the base case (without considering dispersion). The inferred absolute differences in effective radius values between calculations with each of the scaling factors are below 0.8 μm as LWC ranges between 0.1 and 1.0 g m-3. The optical depth decreased by up to 14% (marine), and up to 29% (continental) when dispersion is considered in both effective radius and asymmetry factor (βLDR scaling factor). Correspondingly, the relative change in cloud albedo is up to 6% (marine) and up to 11% (continental) clouds. For continental clouds, the calculated effective radius when dispersion is considered fits well within the measured range of effective radius in SCAR-B project. The calculated cloud albedo when dispersion is considered shows better agreement with the estimated cloud albedo from measured effective radius in SCAR-B project than the cloud albedo calculated without dispersion. In cleaner conditions of marine clouds, only βPL-scaled albedo fits satisfactory within the validity range of albedo inferred using an effective radius-liquid water content relationship proposed by Reid et al. (1999) from ASTEX project. The low correlation coefficient of the effective radius-liquid water content parameterization in ASTEX may also play a role within.  

Total peroxides were analyzed in 26 rainwater samples collected on board of the R/V El Puma of the National Autonomous University of México (UNAM) during the Climatic Experiment in the Americas Warm Water Pools (ECAC-1) over the eastern Pacific Ocean between 12 and 14º N, and between 98 and 100º W, from May 23 to 25, 2001. The volume weighted mean concentration of total peroxides was 13.1 ± 1.94 μM. Also, sulfate ion was analyzed. The volume weighted mean concentrations for sulfate and sea-salt sulfate were 0.76 ± 0.59 and 0.04 ± 0.06 mg L-1, respectively. Excess sulfate (non-sea-salt sulfate) represented 95% of the total sulfate. The total peroxides concentration in rainwater correlated significantly with total sulfate and excess sulfate (0.560 and 0.586 at a p < 0.05, respectively) possibly because most of the excess sulfate and hydrogen peroxide, observed in the Mexican eastern Pacific Ocean, could have been produced from the oxidation of biogenic sulfur compounds. The non-significant correlation between sea-salt sulfate and total peroxides was due to the fact that H2O2 does not react with the sulfate already present in sea salt aerosols. Also, the concentration of total peroxides did not correlate with rain intensity probably because a significant fraction of H2O2 could have been generated within cloud droplets.  

The objective of this work is to provide a detailed description of the onset of the South American Monsoon based on precipitation observations available over tropical and subtropical South America. The analysis was also performed using outgoing longwave radiation (OLR) data in order to assess the ability of this particular dataset to reproduce the main features associated with precipitation evolution during austral spring. Results show that both OLR and precipitation data agree in describing the progression of convection from the northwest and southeast into central Brazil by the beginning of October. Moreover the assessment of available methods to identify onset dates shows that the method of Kousky (1988), based on the OLR evolution, provides the onset date in most of South America, without regionally adaptation, as the methods based on rainfall generally require. Composite fields show that rainfall in central Brazil begins with moderate rates, which are still lower than those observed over the northwestern and southeastern tropical regions. After the rainfall jump, that on average occurs three pentads later than the onset of rainfall, precipitation rates increase over central Brazil and similar rates are observed over the entire tropical region. It is suggested that transient activity, which occurs around the onset period when the atmospheric mean conditions are getting more unstable as they approach summer-like conditions, is the one that imprints a rainfall-jump feature in the precipitation evolution. The character of changes in the precipitation rate, as the rainy season develops, provides complementary information that can be used together with onset date.  

Features of long- and short-range atmospheric transport to El Tajín, an important archaeological site in Veracruz, México, are investigated. The study is motivated by the need for an increased understanding of the meteorological processes contributing to acidic precipitation at Mesoamerican heritage sites, and is part of ongoing investigations of air quality in southeastern México. Using a variety of meteorological resources including global reanalysis fields, upwind trajectory analysis and local wind measurements, we find that both large-scale and local meteorological forcings in the region of the El Tajín archaeological zone favor transport from easterly and northerly sources. Significant acid precursor emissions exist in both of these upwind directions, including a large area of active oil platforms in the Bay of Campeche, about 500 km east or one day upwind of El Tajín.

Peroxyacetylnitrate (PAN) and ozone are considered typical photochemical secondary pollutants and, as such, are expected to reach higher concentrations in periods of high irradiance (summer). However, in Santiago, PAN highest values are reached in autumn. The average of daily maximums are: 4.0 ± 1.7 ppb in autumn (May and June); 0.9 ± 0.5 ppb in winter (July and August); 1.9 ± 1.0 ppb in spring (October and November); 3.1 ± 1.4 ppb in summer (January and March). In autumn the integrated daily values are also considerably higher than in other periods (averages of 38 ppb h in May and 13 ppb h in January). This behavior is related to a lower PAN’s thermal stability in summer. This factor, together with an increased atmospheric stability and lower height of the mixing layer in autumn explains the high levels measured in periods of relatively low solar irradiance.

Mt. Everest is relatively inaccessible and little is known about its meteorology. On 27 April 2005, an automatic weather station was displayed on the north column (28º01′0.95″N, 86º57′48.4″E, 6523 masl) of Mt. Everest. This paper summarizes the meteorological data collected from 1 May to 22 July 2005. The measured variables included long-wave radiation, air temperature, relative humidity and baromteric pressure. The daily record indicates synoptic scale variability in the thermodynamic variables, while short-wave radiation and wind speed decrease gradually at different degree, net radiation changes little with a slight increase, and wind direction turns from north to south.