Ozone Formation Potentials of Volatile Organic Compounds and Ozone Sensitivity to Their Emission in the Megacity of São Paulo, Brazil (original) (raw)
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Determining VOCs Reactivity for Ozone Forming Potential in the Megacity of São Paulo
Aerosol and Air Quality Research, 2018
High ozone (O 3) concentrations are a major concern about air quality in the São Paulo Metropolitan Area (SPMA). During 2016, the 8-hour state standard of 140 µg m-3 was exceeded on 32 days, whereas the 1-hour national standard of 160 µg m-3 was exceeded on 76 days. Exposure to such unhealthy O 3 levels and other pollutants can lead to respiratory disease. The focus of this study is to determine the main O 3 precursor in terms of the volatile organic compounds (VOCs) in order to provide a scientific basis for controlling this pollutant. In this work, 66 samples of hydrocarbons, 62 of aldehydes and 42 of ethanol were taken during the period from September 2011 to August 2012 from 7:00 to 9:00 a.m. The OZIPR trajectory model and SAPRC atmospheric chemical mechanism were used to determine the major O 3 precursors. During the studied period, aldehydes represented 35.3% of the VOCs, followed by ethanol (22.6%), aromatic compounds (15.7%), alkanes (13.5%), ketones (6.8%), alkenes (6.0%) and alkadienes (less than 0.1%). Considering the concentration of VOCs and their typical reactivity, the simulation results showed that acetaldehyde contributed 61.2% of the O 3 formation. The total aldehydes contributed 74%, followed by aromatics (14.5%), alkenes (10.2%), alkanes (1.3%) and alkadienes (e.g., isoprene; 0.03%). Simulation results for the SPMA showed that the most effective alternative for limiting the O 3 levels was reducing the VOC emissions, mainly the aldehydes.
Main ozone-forming VOCs in the city of Sao Paulo: observations, modelling and impacts
Air Qual Atmos Health, 2017
High-ozone concentrations currently represent the main air pollution problem in the city of São Paulo, Brazil. To elucidate the main volatile organic compounds (VOCs), which act as ozone precursors, samples from air quality monitoring stations were evaluated. Thirty-five samples were collected in August-September of 2006 and 43 in July-August of 2008, when the consumption of ethanol was about 50 % of the total fuel used in the São Paulo Metropolitan Area. Samples were collected using electropolished stainless canisters. Chemical analyses were performed on pre-concentrated samples followed by gas chromatograph with flame ionization and mass spectrometry detection. The incremental reactivity scale was used to rank the ozone precursors using the Ozone Isopleth Package for Research (OZIPR) trajectory model coupled with chemical mechanism Statewide Air Pollution Research Center (SAPRC). Sixty-nine species of VOCs were quantified, and the ten main ozone precursors identified in 2008 were as follows: formaldehyde (42.8 %), acetaldehyde (13.9 %), ethene (12.2 %), propene (5.1 %), 1-methylcyclopentene (3.0 %), p-xylene (2.4 %), 1-butene (2.1 %), trans-2-pentene (1.9 %), 2-methyl 2-butene (1.7 %) and trans-2-butene (1.6 %). Volatile organic compound mass distribution showed that in 2008 alkanes represented 46 % of the total VOCs, alkenes 27 %, aromatics 14 %, alkadienes 1 % and aldehydes 12 %.
Simplified Modeling of Tropospheric Ozone Formation Considering Alternative Fuels Using
Anuário do Instituto de Geociências - UFRJ, 2014
Brazilian cities have been constantly exposed to air quality episodes of high ozone concentrations (O 3). Known for not be emitted directly into the environment, O 3 is a result of several chemical reactions of other pollutants emitted to atmosphere. The growth of vehicle fleet and government incentives for using alternative fuels like ethanol and Compressed Natural Gas (CNG) are changing the Brazilian Metropolitan Areas in terms of acetaldehyde and formaldehyde emissions, Volatile Organic Compounds (VOC's) present in the atmosphere and known to act on the kinetics of ozone. Driven by high concentrations of tropospheric ozone in urban/industry centers and its implications for environment and population health, the target of this work is understand the kinetics of ozone formation through the creation of a mathematical model in FORTRAN 90, describing a system of coupled ordinary differential equations able to represent a simplified mechanism of photochemical reactions in the Brazilian Metropolitan Area. Evaluating the concentration results of each pollutant were possible to observe the precursor's influence on tropospheric ozone formation, which seasons were more conducive to this one and which are the influences of weather conditions on formation of photochemical smog.
Ozone precursors for the São Paulo Metropolitan Area
Science of The Total Environment, 2010
Ozone represents the main atmospheric pollutant in the São Paulo Metropolitan Area (SPMA). In this region, its concentration exceeds the national air quality standards for several days out of the year. Ozone is a secondary pollutant and is a product of VOCs, NO x , and sunlight. Thus, it is very difficult to elaborate efficient strategies for its reduction. Computational simulations may provide an interesting alternative to evaluate the many factors that affect ozone formation. In this study, the trajectory model OZIPR was used together with the SAPRC chemical mechanism to determine the incremental reactivity scale for VOCs in the SPMA. VOC input data were obtained from two campaigns that were performed in the studied area in 2006. Values for CO, NO x , and meteorological parameters were obtained by automatic monitors. Five base-cases were created to verify the variation in maximum ozone concentration and thus determine the ozone formation potential of each VOC. NO x and VOC emissions were independently and simultaneously reduced by 5, 10, 20, and 30% to verify variations in ozone formation. With the simulator output data, ozone isopleths charts were generated for the city of São Paulo. Analysis of the obtained results shows that the most frequent compounds found among the ten main ozone precursors in São Paulo, using the reactivity scales created from the five base-cases, were: formaldehyde, acetaldehyde, propene, isoprene, cis-2-butene, and trans-2-butene, with formaldehyde being always the main ozone precursor compound. The simulations also show that an efficient strategy to decrease ozone concentrations in the SPMA would be to reduce total VOC emissions. The same strategy is not possible for NO x , as the reduction of these pollutants would increase ozone concentrations.
Monitoring of tropospheric ozone precursors in the Metropolitan Area of São Paulo
In recent years, the ambient concentrations of tropospheric ozone in the Metropolitan Area of São Paulo (MASP) reached levels of more than five times those considered safe for public health according to the World Health Organization (WHO). Since volatile organic compounds (including hydrocarbons, carbonyl compounds and alcohols), NOx and ultraviolet radiation (λ ≤ 394nm) have a key role in the formation of this pollutant, the current study presents data from continuous sampling and analysis of these precursors to the formation of tropospheric ozone in São Paulo city. The hydrocarbons and ozone were continuously sampling and analyzed automatically 24 hours a day. Statistical analyses were applied to the base data to evaluate the winds direction effects on the hydrocarbons variability. The main focus was to find specific tracers for the fuels used in São Paulo.
2015
Using a method developed by Lurmann et al. (1991), for lumped molecule or lumpedsurrogate, we were able to define the respective base mixture for determining the re activity of volatile organic compounds (VOCs) in ozone formation in the Mexico City metropolitan area (MCMA). A sampling campaign for collecting VOCs was carried out to determine the individual compounds in the MCMA atmosphere. Samples were collected simultaneously in stainless steel canisters at six sites: Xalostoc, Pedregal, Tlalnepantla, Cerro de la Estrella, Instituto Mexicano del Petroleo, and la Merced. Seven samples were taken at each site during the sampling period. Ten VOC groups were established applying the Lurmann methodology, and each group was represented by one compound as follows: i) n-butane for the first alkane group, ii) n-octane for the second alkane group, iii) ethylene in a group by itself, iv) propene for the first olefin group, v) t-2-butene for the second olefin group, vi) toluene for mono alkyl ...
Atmospheric Chemistry and Physics, 2007
An episodic simulation is conducted to characterize ozone (O 3) photochemical production and investigate its sensitivity to emission changes of ozone precursors in the Mexico City Metropolitan Area (MCMA) using the Comprehensive Air Quality Model with extensions (CAMx). High O x (O 3 +NO 2) photochemical production rates of 10-80 ppb/h are predicted due to the high reactivity of volatile organic compounds (VOCs) in which alkanes, alkenes, and aromatics exert comparable contributions. The predicted ozone production efficiency is between 4-10 O 3 molecules per NO x molecule oxidized, and increases with VOC-to-NO 2 reactivity ratio. Process apportionment analyses indicate significant outflow of pollutants such as O 3 and peroxyacetyl nitrate (PAN) from the urban area to the surrounding regional environment. PAN is not in chemicalthermal equilibrium during the photochemically active periods. Sensitivity studies of O 3 production suggest that O 3 formation in the MCMA urban region with less chemical aging (NO z /NO y <0.3) is VOC-limited. Both the simulated behavior of O 3 production and its sensitivities to precursors suggest that midday O 3 formation during this episode is VOC sensitive in the urban region on the basis of the current emissions inventory. More episodic studies are needed to construct a comprehensive and representative picture of the O 3 production characteristics and its response to emission controls.
Atmospheric …, 2006
Ozone concentrations in the heavily polluted metropolitan area of Sa˜o Paulo (MASP), in Brazil, frequently exceed established international standards. This study aims to describe the impact that three meteorological variables (mixing height, wind speed and air temperature) on the ozone concentration, as well as reactive hydrocarbon (RHC) limitation and nitrogen oxide (NO x ) limitation, have on ozone formation in the area. To achieve these objectives the California Institute of Technology (CIT) Eulerian air quality model was applied combined with the same methodology described in Baertsch-Ritter et al. [2004. Atmospheric Chemistry and Physics 4, 423-438] In addition, NO x and RHC emission inventory reductions were used to evaluate their sensitivities in the CIT model. A simulation of an episode occurring in the MASP on 22 August 2000, when a peak ozone level of 127 ppbv was recorded, is presented. In the CIT model results for the base case, primary pollutant concentrations and ozone concentrations are in good agreement with the measured data. In addition, changes in mixing height, wind speed and air temperature input files have the greatest effect on peak ozone in the MASP, and the isolated effect of RHC emission inventory reduction leads to 26% lower ozone levels than in the base case. Based on the results of this study, we can conclude that with reduction of RHC emission could provide the best scenario for promoting lower ozone concentrations in the MASP. r
Journal of Geophysical Research, 2004
1] Emissions of volatile organic compounds (VOCs) and of CO are often underestimated, and correcting this underestimate is important for modeling ozone formation and sensitivity. The California Institute of Technology three-dimensional photochemical model is used to test the official emissions inventory for the Mexico City metropolitan area through a direct comparison of measured and modeled total nonmethane hydrocarbons (NMHCs) and CO. The model is applied to six 2-day periods during the IMADA measurement campaign of March 1997. When using emissions based on the official emissions inventory, the model significantly underestimates measurements of total NMHCs and of CO. A best fit to the measurements (with lowest bias) is found when increasing emissions of CO and VOCs by factors of 2 and 3, respectively. Adjusting total emissions accordingly, the model produces good estimates of ozone and NO x , with average normalized biases over 6 days of 3% and 32%, respectively, and with better agreement during daytime hours. This agreement for ozone and NO x supports the suggestion that VOC and CO emissions are underestimated. Other uncertainties are analyzed, finding that while some uncertainties are important, none is individually significant enough to account for the discrepancy. Correcting the total emissions, the overall model performance is found to be adequate, particularly on 3 days, for the model to be used for analysis of control strategies. Using the results of a chemical mass balance identification of NMHC sources highlights sources that are more likely underestimated, but confidence in the appropriate correction to emissions from different sources is low and should be investigated further.