Browsing by Author "Castro, Julio"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Analysis of urban pollution episodes by inverse modeling
    (PERGAMON-ELSEVIER SCIENCE LTD, 2010) Jorquera, Hector; Castro, Julio
    Urban pollution episodes pose two relevant issues: a) was the episode controlled by specific meteorology, a rise of emissions or both? b) Were mitigation measures effective in curbing down pollution? A methodology for answering those questions comes from an inverse modeling approach. In this work we have applied the methodology to the city of Santiago, Chile for which the required input data are available. We use a Kalman filter and ambient observations to constrain sources of tracers such as CO, elemental carbon and suspended street dust. The period analyzed is the week from May 20th till May 26th 2005. We find that a posteriori CO emissions were 76% of the a priori estimates. For suspended street dust a posteriori values are 36% and 21% of the prior values for coarse and fine fractions, respectively. Elemental carbon emissions are underestimated in the prior inventory - we find a correction factor of 1.53 for the whole week. Sensitivity analyses tested the robustness of a posteriori estimates, generating ensembles of simulations for different modeling options. For different initial prior estimates, the ratio of standard deviation to mean values was below 0.20 for 75% of the a posteriori, estimated emissions. For different choices of the error covariance matrices and model errors those ratios were below 0.30 for 75% of a posteriori emissions, which shows the robustness of results for different parameter choices - only a small fraction of results were not significant. The high pollution peaks on May 21st are due to specific meteorological conditions and increased traffic emissions as well. Contingency measures taken on Sunday May 22nd and better dispersion conditions on Monday May 23rd stopped the accumulation of those pollutants, showing the effectiveness of short term strategies such as traffic bans and street sweeping operations in curbing down traffic pollution at Santiago. (C) 2009 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Application of MM5/CALMET/CAMx in Santiago, Chile
    (2003) Jorquera, Héctor; Castro, Julio; Escobar, Jaime; Jakobs, Hermann
    The Comprehensive Air Quality Model with Extensions (CAMx) has been applied to two summer photochemical episodes in the greater metro area of Santiago, Chile. It is shown that the CAMx model predicts reasonably well the spatial gradients of gaseous pollutants and the weekly cycle of variation for CO and NOx. The emission estimates for CO seem to be quite on agreement with actual emissions in 2000. NOx emissions are more appropriate for the 1998 scenario, whereas for 2000 they seem to overestimate actual emissions, so the mobile sources emission factors need to be verified. The SO2 simulations indicate that there relevant sources not accounted for in the inventory. There are problems with the VOC emissions for the area sources, because the model predictions for ozone are quite below what is being observed, for all network stations in 1998, a scenario with reliable NOx simulated levels. For the 2000 scenario, this problem is worsened because of excessive ozone scavenging. When we use the results of a comprehensive VOC campaign to produce a synthetic VOC profile of emissions for the whole city, simulated ozone gets closer to ambient measurements for the 1998 scenario. For the 2000 scenario, the overestimation in the simulated NOx levels is large enough to prevent any significant ozone sensitivity with respect to VOC increases. All things considered, CAMx has passed the "proof of the concept" for studying photochemical episodes at Santiago, Chile. The major sources of uncertainty are the emission inventory estimates for NOx and VOC. As a second source of uncertainty, meteorology was not properly represented on the second half of the January 1998 episode, and there are some problems with the stations closer to the Andes foothills overnight, particularly regarding ozone nocturnal profiles, that deserve further research.
  • No Thumbnail Available
    Item
    Carbon monoxide concentrations in Santiago City at street levels and their vertical gradient
    (2008) Rubio, María A.; Lissi, Eduardo; Jorquera, Héctor; Salinas, Elizabeth; Castro, Julio; Cádiz, Marcela
    Carbon monoxide concentrations were measured at ground level (1 m) near heavy traffic streets in downtown Santiago de Chile in periods of low (November and December), intermediate (April) and high (May) ambient concentrations. Also, measurements were carried out at several heights (from 1 to 127 m) in Santiago's main street during winter time. Measurements carried out at ground level show maximum values during the morning rush hour, with values considerably higher than those reported by the urban air quality network, particularly in summer time. However, the measured values are below air quality standards. Vertical CO profiles were measured in a tower located in the center of downtown. Below 40 m (average altitude of neighboring buildings), the profiles do not show a consistent vertical gradient, with CO concentrations increasing or decreasing with height, regardless of atmospheric stability. In this low altitude range, the observed vertical profiles are poorly predicted by a street canyon model, and the measured concentrations can not be described by a simple exponential decay. At higher altitudes (40 and 127 m) a negative gradient in CO concentrations is observed, both for stable and unstable atmospheric conditions. The values of CO measured at 127 m are relatively well described by an Eulerian dispersion model running with current CO emission inventories for Santiago, although this model tends to predict stepper CO gradients than the observed ones.