Luciana Vanni Gatti

Ozone precursors for the São Paulo Metropolitan Area.

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.

Estudos dos compostos orgânicos voláteis precursores de ozônio na cidade de São Paulo

O ozonio e o principal problema de poluicao do ar na cidade de Sao Paulo. Este estudo, que foi realizado em uma estacao de monitoramento da qualidade do ar da Companhia de Tecnologia de Saneamento Ambiental (CETESB), enfoca a elucidacao dos principais compostos orgânicos volateis precursores de ozonio na atmosfera paulistana. Foram coletadas 36 amostras nos meses de agosto e setembro de 2006, nos quais o consumo de etanol era de aproximadamente 50% nesta epoca. Foram quantificadas 69 especies de compostos orgânicos volateis, nos quais os dez compostos mais importantes na formacao de O3 foram: 1-buteno (6,8%), eteno (6,5%), formaldeido (6,1%), acetaldeido (5,5%), tolueno (4,8%), 1-etil-4-metilbenzeno (3,7%), trans-2-penteno (3,7%), propeno (3,7%), trans-2-buteno (3,5%) e 1-metilciclopenteno (3,5%). As classes mais abundantes em concentracao no ar foram: alcanos (45%), alcenos (26%), aromaticos (14%), aldeidos (13%) e alcadienos (2%).

Measurements of emissions from motorcycles and modeling its impact on air quality

The increase in the number of motorcycles in large Brazilian cities is due to several factors such as traffic, low cost, mobility, few parking lots and the low efficiency of public transportation, becoming an important factor in air quality deterioration. In this context, vehicle emissions monitoring is essential to understand the contribution to air pollution as a whole. In this scenario, the emissions were sampled on a motorcycle dynamometer test bench and analyzed by gas chromatography and on-line analyzers according to the EC/97/24 standard (European Commission). Emissions from motorcycles using commercial gasoline (with 22% of ethanol) were used in combination with meteorological data and ambient air pollutants for Rio de Janeiro City (Brazil) during the Winter of 2011, using the trajectory model OZIPR (Ozone Isopleth Package for Research) and the chemical model SAPRC99 (State-wide Air Pollution Research Centre) to assess the impact on the ozone formation in the troposphere of Rio de Janeiro for the next several years. The results indicate that ozone levels will exceed the established limits by national legislation within three years. The study also showed that pollutant emission rates stay in agreement with emissions recommended by the Brazilian legislation for all phases. The increase in ozone concentration occurs due to high emissions of reactive volatile organic compounds in an atmosphere with high levels of nitrogen oxides (NOx). Given this scenario, additional measures are necessary to manage emissions from mobile sources in the future.

Main ozone-forming VOCs in the city of Sao Paulo: observations, modelling and impacts

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 50xa0% 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 (42.8xa0%), acetaldehyde (13.9xa0%), ethene (12.2xa0%), propene (5.1xa0%), 1-methylcyclopentene (3.0xa0%), p-xylene (2.4xa0%), 1-butene (2.1xa0%), trans-2-pentene (1.9xa0%), 2-methyl 2-butene (1.7xa0%) and trans-2-butene (1.6xa0%). Volatile organic compound mass distribution showed that in 2008 alkanes represented 46xa0% of the total VOCs, alkenes 27xa0%, aromatics 14xa0%, alkadienes 1xa0% and aldehydes 12xa0%.

Tropical land carbon cycle responses to 2015/16 El Niño as recorded by atmospheric greenhouse gas and remote sensing data

The outstanding tropical land climate characteristic over the past decades is rapid warming, with no significant large-scale precipitation trends. This warming is expected to continue but the effects on tropical vegetation are unknown. El Niño-related heat peaks may provide a test bed for a future hotter world. Here we analyse tropical land carbon cycle responses to the 2015/16 El Niño heat and drought anomalies using an atmospheric transport inversion. Based on the global atmospheric CO2 and fossil fuel emission records, we find no obvious signs of anomalously large carbon release compared with earlier El Niño events, suggesting resilience of tropical vegetation. We find roughly equal net carbon release anomalies from Amazonia and tropical Africa, approximately 0.5 PgC each, and smaller carbon release anomalies from tropical East Asia and southern Africa. Atmospheric CO anomalies reveal substantial fire carbon release from tropical East Asia peaking in October 2015 while fires contribute only a minor amount to the Amazonian carbon flux anomaly. Anomalously large Amazonian carbon flux release is consistent with downregulation of primary productivity during peak negative near-surface water anomaly (October 2015 to March 2016) as diagnosed by solar-induced fluorescence. Finally, we find an unexpected anomalous positive flux to the atmosphere from tropical Africa early in 2016, coincident with substantial CO release. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

Volatile Organic Compounds in a Residential and Commercial Urban Area with a Diesel, Compressed Natural Gas and Oxygenated Gasoline Vehicular Fleet

Air samples were collected in a typical residential and commercial area in Rio de Janeiro, Brazil, where buses and trucks use diesel and light duty vehicles use compressed natural gas, ethanol, and gasohol (gasoline blended with ethanol) as fuel. A total of 66 C3–C12 volatile organic compounds (VOCs) were identified. The most abundant compounds, on a mass concentration basis, included propane, isobutane, i-pentane, m,p-xylene, 1,3,5-trimethylbenzene, toluene, styrene, ethylbenzene, isopropylbenzene, o-xylene and 1,2,4-trimethylbenzene. Two VOCs photochemical reactivity rankings are presented: one involves reaction with OH and the other involves production of ozone.

COMPOSTOS ORGÂNICOS VOLÁTEIS: PRINCIPAIS PRECURSORES DE OZÔNIO NA CIDADE DE SÃO PAULO

The main air quality problems registered in the in the city of Sao Paulo are caused by ozone (O 3 ) concentrations. This study, which was carried out in the Brazilian Basic Sanitation Engineering Company (CETESB) monitoring station of air quality located in the University of Sao Paulo - USP, focused on the elucidation of the main volatile organic compounds (VOCs) ozone precursors in Sao Paulo atmosphere between January to December 2006. Seventy-eight samples of air were collected during the study period, which the ten most important compounds in the formation of O3 were but-1-ene (12%), propene (10%), ethylene (8%), p-xylene (7% ) buta-1,3-diene (6%), 1-ethyl-4-methylbenzene (4%), isoprene (4%), trans-but-2-ene (4%), 2-methyl-but-2-ene (4%) and cis-but-2-ene (3%). The most abundant classes concentration in the air were alkanes (45%), alkenes (26%), and aromatics (14%), aldehydes (13%) and alkadienes 2%.