DSpace Angular :: Browsing by Author "Jorquera, H"

Browsing by Author "Jorquera, H"

Now showing 1 - 11 of 11

A ground-level ozone forecasting model for Santiago, Chile
(WILEY-BLACKWELL, 2002) Jorquera, H; Palma, W; Tapia, J
A physically based model for ground-level ozone forecasting is evaluated for Santiago, Chile. The model predicts the daily peak ozone concentration, with the daily rise of air temperature as input variable; weekends and rainy days appear as interventions. This model was used to analyse historical data, using the Linear Transfer Function/Finite Impulse Response (LTF/FIR) formalism; the Simultaneous Transfer Function (STF) method was used to analyse several monitoring stations together. Model evaluation showed a good forecasting performance across stations-for low and high ozone impacts-with power of detection (POD) values between 70 and 100%, Heidke's Skill Scores between 40% and 70% and low false alarm rates (FAR). The model consistently outperforms a pure persistence forecast. Model performance was not sensitive to different implementation options. The model performance degrades for two- and three-days ahead forecast, but is still acceptable for the purpose of developing an environmental warning system at Santiago. Copyright (C) 2002 John Wiley Sons, Ltd.
A neural network estimator for total biomass of filamentous fungi growing on two dimensional solid substrate
(KLUWER ACADEMIC PUBL, 1998) Acuna, G; Giral, R; Agosin, E; Jorquera, H; Perez Correa, R; Ferret, E; Molin, P; Thibault, J
A neural network dynamic model is proposed for the on-line estimation of total biomass during filamentous fungi cultures on two dimensional solid substrate. The neural network provides an accurate and robust estimation of biomass from macroscopic measurements of the colony radius evolution. Experiments were performed on Gibberella fujikuroi growing on Petri dishes under different conditions of temperature and water activity.
Air quality at Santiago, Chile: a box modeling approach II. PM(2.5), coarse and PM(10) particulate matter fractions
(PERGAMON-ELSEVIER SCIENCE LTD, 2002) Jorquera, H
Ambient monitored data at Santiago, Chile, are analyzed using box models with the goal of assessing contributions of different economic activities to air pollution levels. The box modeling approach was applied to PM(10), PM(2.5) and coarse (PM(10)-PM(2.5)) particulate matter (PM) fractions; the period analyzed is 1989-1999, A linear model for each PM fraction was obtained, having as independent variables CO and SO(2) concentrations, plus a term proportional to (wind speed)(-1) that lumps together non-combustion emissions and secondary generation terms; wet scavenging is included as another independent variable, Model identification results show good agreement for the different parameters across monitoring stations. The washout ratios and scavenging coefficients agree with data published in the literature, being higher for the coarse PM fraction. The CO and SO(2) coefficients fitted for 1989-1995 agree with a priori estimates for the same period. Background estimates for the PM fractions are in agreement with measurement campaigns in upwind sites. Results show that transportation sources have become the dominant contributors to ambient PM levels, while stationary sources have decreased their contributions in the last years. The relative importance of mobile sources to PM2.5 ambient concentrations has doubled in the last 10 years, whereas stationary sources have reduced their relative contributions to half the value in the early 1990s. Model estimates of regional background of PM(2.5) and PM10 have decreased 50% and 22% in the last decade, respectively; coarse background has shown no significant change. The final conclusion is that there is room and need for a more intensive emission reduction strategy for Santiago, focusing on mobile sources. The approach pursued in this work is feasible for cities or regions where comprehensive, transport and chemistry models are not available yet, but estimates of air quality contributions are needed for policy purposes. The methodology requires data on ambient air quality measurements and surface meteorology. (C) 2002 Elsevier Science Ltd. All rights reserved.
Air-pollution modelling in an urban area: Correlating turbulent diffusion coefficients by means of an artificial neural network approach
(PERGAMON-ELSEVIER SCIENCE LTD, 2006) Perez Roa, R; Castro, J; Jorquera, H; Perez Correa, JR; Vesovic, V
The vertical pollutant dispersion is quite sensitive to the eddy diffusivity, K-V. Therefore, good estimations of K-V are essential for improving the predictive performance of Eulerian dispersion models; especially in urban areas where literature based K-V correlations are not always accurate. Here, we present a methodology to obtain a more accurate, but site-specific, Kv correlation. It is based on using artificial neural networks (ANN) to find the best Kv function for a particular urban area by minimizing, in a least-squares sense, the difference between ambient measurements of carbon monoxide and dispersion simulations of this tracer species. The resulting ANN-K-V correlation is a function of three parameters namely, the stability parameter (z/L), the height within the mixing layer (z/h), and the scaled height (zf(C)/u(*))-hence the Monin-Obukhov (L), mixing (h) and Ekman (u(*)/f(C)) lengths are used to predict Kv across the atmospheric boundary layer.
An intervention analysis of air quality data at Santiago, Chile
(PERGAMON-ELSEVIER SCIENCE LTD, 2000) Jorquera, H; Palma, W; Tapia, J
Air quality data at Santiago, Chile (PM10, PM2.5 and ozone) from 1989 to 1998 are analyzed with the goal of estimating trends in and impacts of public policies on air quality levels. Those policies, in effect since the late 1980s, have been essentially aimed at PM10 pollution abatement. The analyses show that fall and winter air quality has been improving consistently, specially the PM2.5 levels. The estimated trends for the monthly averages of PM10 concentrations range from - 1.5 to - 3.3% per annum, whereas the trends for monthly averages of PM2.5 concentrations range from - 5 to - 7% per annum. The monthly averages of ground ozone daily maxima do not have a significant trend for two of the downtown monitor sites; at the other three monitoring sites (including the one with the highest impacts) there is a clear downward trend between - 5 and - 3% per annum. The seasonal averages of a declimatized ozone production rate show a downward trend from 1988 through 1995, and no additional improvements have occurred thereafter. These mixed results for ground ozone levels are ascribed to a shift in the magnitude and spatial distribution of emissions in the city, and so there is a need for additional ozone abatement policies and further research on air pollution abatement options. (C) 2000 Elsevier Science Ltd. All rights reserved.
An urban photochemistry study in Santiago de Chile
(PERGAMON-ELSEVIER SCIENCE LTD, 2005) Rappengluck, B; Schmitz, R; Bauerfeind, M; Cereceda Balic, F; von Baer, D; Jorquera, H; Silva, Y; Oyola, P
During spring time 2002 a field experiment was carried out in the Metropolitan Area of Santiago de Chile at three monitoring sites located along a SW-NE transect that represents upwind, downtown and downwind conditions, respectively. Three consecutive days (30 October-01 November 2002) reflecting different photochemical and meteorological conditions were selected. These days included two workdays and one holiday and thus the effect of different primary emissions could be investigated. A variety of trace gas measurements (O-3, NOx, CO, volatile organic compounds (VOC)) were obtained at these sites. Alkanes represent the largest VOC fraction at all sites, followed by aromatics and alkenes, the smallest fractions are represented by the alkynes or isoprene. Regarding reactivity ranking propene equivalent values show that during morning hours, alkenes are the most reactive compounds, at noon, aromatics are dominant, and in the afternoon isoprene becomes important. Alkanes do not contribute more than 20% to the total air mass reactivity despite being present at the higher concentration levels. Regarding liquefied petroleum gas (LPG) impacts, we find a threefold decrease of concentrations at the eastern side of the city-and no significant trend at Downtown Santiago-which we ascribe to a switch to natural gas in the higher income eastern side of town. The generation of ozone impacts above 50 ppbv is mainly due to anthropogenic traffic-related hydrocarbons. In addition, traffic emissions are contributing most to the formation of secondary organic aerosols (SOA). A model study was carried out, applying a Lagrange trajectory model coupled with photochemical and aerosol modules. The model results are in good agreement with the observations. Additionally, the relative contribution of the respective hydrocarbons to the ozone production in an air parcel along the trajectory was computed. The model also indicates SOA formation by means of oxidation of higher alkanes, alkenes, and aromatics, the latter being the major contributors to those secondary pollutants. (c) 2005 Elsevier Ltd. All rights reserved.
Data analysis using regression models with missing observations and long-memory: an application study
(ELSEVIER, 2006) Iglesias, P; Jorquera, H; Palma, W
The objective of this work is to propose a statistical methodology to handle regression data exhibiting long memory errors and missing values. This type of data appears very often in many areas, including hydrology and environmental sciences, among others. A generalized linear model is proposed to deal with this problem and an estimation strategy is developed that combines both classical and Bayesian approaches. The estimation methodology proposed is illustrated with an application to air pollution data which shows the impact of the long memory in the statistical inference and of the missing values on the computations. From a Bayesian standpoint, genuine priors are considered for the parameters of the model which are justified within the context of the air pollution model derivation. (c) 2005 Elsevier B.V. All rights reserved.
Forecasting ozone daily maximum levels at Santiago, Chile
(PERGAMON-ELSEVIER SCIENCE LTD, 1998) Jorquera, H; Perez, R; Cipriano, A; Espejo, A; Letelier, MV; Acuna, G
In major urban areas, air pollution impact on health is serious enough to include it in the group of meteorological variables that are forecast daily. This work focusses on the comparison of different forecasting systems for daily maximum ozone levels at Santiago, Chile. The modelling tools used for these systems were linear time series, artificial neural networks and fuzzy models. The structure of the forecasting model was derived from basic principles and it includes a combination of persistence and daily maximum air temperature as input variables. Assessment of the models is based on two indices: their ability to forecast well an episode, and their tendency to forecast an episode that did not occur at the end (a false positive). All the models tried in this work showed good forecasting performance, with 70-95% of successful forecasts at two monitor sites: Downtown (moderate impacts) and Eastern (downwind, highest impacts). The number of false positives was not negligible, but this may be improved by expressing the forecast in broad classes:low, average, high, very high impacts; the fuzzy model was the most reliable forecast, with the lowest number of false positives among the different models evaluated. The quality of the results and the dynamics of ozone formation suggest the use of a forecast to warn people about excessive exposure during episodic days at Santiago. (C) 1998 Elsevier Science Ltd. All rights reserved.
Macroscopic growth of filamentous fungi on solid substrate explained by a microscopic approach
(JOHN WILEY & SONS INC, 1999) Ferret, E; Simeon, JH; Molin, P; Jorquera, H; Acuna, G; Giral, R
A quantitative model predicting biomass growth an solid media has been developed. The model takes into account steric interactions between hyphae and tips at the microscopic level (competition for substrate and tip-hypha collisions), These interactions effect a slowing down of the hyphal, population-averaged extension rate and are responsible, at the microscopic level, for the distribution of tip orientations observed at the colony border. At the macroscopic level, a limiting value of the colony radial extension rate is attained. A mathematical model that combines hyphal branching, tip diffusion, and biomass growth was proposed to explain such behavior. Experiments using Gibberella fujikuroi were performed to validate the model; good agreement between experiments and simulations was achieved. Most parameters can be measured by simple image analysis on the peripheral growth zone, and they have clear physical meaning; that is, they correspond to properties of single, leading hyphae. The model can be used to describe two-dimensional (2D) solid media fermentation experiments under varying culture conditions; the model can also be extended to consider growth in three-dimensional (3D), complex geometry substrates. (C) 1999 John Wiley & Sons, Inc.
Receptor modeling of ambient VOC at Santiago, Chile
(PERGAMON-ELSEVIER SCIENCE LTD, 2004) Jorquera, H; Rappengluck, B
Ambient VOC measured at a 1996 spring campaign at Santiago, Chile, have been analyzed using the receptor models UNMIX and Positive Matrix Factorization (PMF). The ambient campaign took place at two sites: a downtown site, close to major traffic emissions, and a residential site, downwind of major industrial sources and highways. At the downtown site the following source apportionments estimates were obtained: fuel evaporation, 29.1 +/- 1.1%; gasoline exhaust, 22.0 +/- 3.4%; diesel exhaust, 18.1 +/- 2.9%; biogenic, LPG and evaporative emissions, 18.0 +/- 3.4%, unexplained: 12%. At the residential site, the following source apportionment was obtained: transported gasoline exhaust, 31.2 +/- 4.1%; local gasoline exhaust, 25.5 +/- 4.0%; evaporative losses, 11.7 +/- 2.8%; LPG losses, 11.0 +/- 2.5%; biogenic emissions, 7.7 +/- 1.7%; diesel exhaust, 6.2 +/- 1.5%; unexplained, 7.7%. Thus, near 70% of ambient VOC impacts at both sites are due to mobile sources. The receptor analyses produced source profiles that had distinctive, dominant compounds; in addition, source contributions exhibited diurnal profiles that were consistent with ambient temperature and wind speed data, and the expected activity patterns within the city. Typical errors in the source contributions vary between 15% for the larger sources-like gasoline exhaust-and 25% for the smaller sources-like biogenic emissions. It was found that the number of factors given by the UNMIX model was a good starting point to refine the solution using PMF. Both models showed good performance at discriminating between source profiles that had similar compositions in subsets of common species, but PMF was able to find better, cleaner source profiles that did UNMIX. At both monitoring sites LPG losses appear mixed in with other source profiles, and this feature could not be solved by adding more source profiles in the analyses; this was likely due to a lack of C-3 measurements needed to better resolve an LPG source profile. (C) 2004 Elsevier Ltd. All rights reserved.
Trends in air quality and population exposure in Santiago, Chile, 1989-2001
(INDERSCIENCE ENTERPRISES LTD, 2004) Jorquera, H; Orrego, G; Castro, J; Vesovic, V
This study focused on establishing trends in the period 1988-2001 in PM2.5, PM10 and ozone concentrations in Santiago, Chile, and linking those to population exposure. There is strong seasonality in the concentration levels, driven by prevailing meteorological conditions, with the concentration of particulates peaking at the beginning of winter, whereas the ozone concentration is highest during the summer. The levels of PM2.5 and PM10 have substantially decreased since the late 1980s and so has the population exposure. Nevertheless, the majority of the population is still exposed to annual average levels that are above standard values. The situation with ozone exposure is different; no substantial decrease can be observed in the data. If anything certain parts of Santiago, notably the south-east, have shown increased levels of ozone. Overall population exposure indicates that the average person was more at risk of ozone in the year 2000 than they were in 1993.

Browsing by Author "Jorquera, H"

Results Per Page

Sort Options