A23C-01 INVITED
Air Pollution in the Mexico Megacity
Mexico City is a megacity whose metropolitan area includes the country federal district, 18 municipalities of the State of Mexico. In year 1992, only 16 municipalities of the State of Mexico were part of MCMA. In year 1940 the Mexico City population was 1.78 millions in an area of 118 km2, in year 2000 the population was 17.9 millions in an area of 1,500 km2. Population has grown a ten fold whereas population density has dropped 20%. Total number of private cars has grown from 2,341,731 in year 1998 to 2,967,893 in year 2004. Nowadays, people and goods travel longer at lower speed to reach school, work and selling points. In addition highly efficient public transport lost a significant share of transport demand from 19.1 in 1986 to 14.3 in 1998. Air pollution is a public concern since early eighties last century; systematic public efforts have been carried out since late eighties. Energy consumption has steadily increased in the MCMA whereas emissions have also decreased. From year 2000 to 2004, the private cars fleet increased 17% whereas CO, NOx and COV emissions decreased between 20-30%. Average concentrations of criteria pollutants have decreased The number of days that the one-hour national standard for bad air quality was exceeded in year 1990 was 160. In year 2005 was 70. Research efforts and public policies on air pollution have been focused on public health. We are now better able to estimate the cost in human lives due to air pollution, or the cost in labor lost due to illness. Little if none at all work has been carried out to look at the effect of air pollution on private and public property or onto the cultural heritage. Few reports have can be found on the impact of air pollution in rural areas, including forest and crops, around the mega city. Mexico City is in the south end of a Valley with mountain ranges higher than 1000 m above the average city altitude. In spite the heavy loss of forested areas to the city, the mountains still retain large forest under strong demographic pressure and under heavy impact of air pollution. Flow patterns induced by complex terrain in the center of Mexico induce strong interaction between the mega city and the rural areas in the Mexico Basin. In and out mesoscale transport to and from the neighboring valleys with cities already larger than one million inhabitants increase the complexity of air pollution processes. Fast urbanization in these valleys suggests even more complicated and full of concerns scenarios. Some recent results on these issues will be shown.
A23C-02 INVITED
Air Quality Impairment Associated to Local and Regional Pollutants Sources in the Megacity of Sao Paulo, Brazil
The Metropolitan Area of Sao Paulo (MASP), with more than 19 million inhabitants in 2006, about 2000 major industrial facilities, and more than 7 million vehicles based on diesel, gasoline, and ethanol, has 8051 km2. MASP is one of the biggest urban agglomerate in the world. Associated to its dimension many important problems appear and among them the bad air quality is one of the most important due to the human health effects. MASP is the richest area in Brazil representing 17% of Brazilian GNP in 2000. Not only the high pollutants concentration but also the accentuated modification of the land use in the area resulted in bad quality of life characterized by local and regional climate modification, as for instance the light rain suppression and the increase of the heavier rain. In MASP the air pollution has worsened due to the cumulative effects of population growth, industrialization and increased vehicle use. Currently there are about 7.2 million passenger and commercial vehicles: 93.5% light- duty and 6.5% heavy-duty diesel vehicles. Of the light-duty vehicles, approximately 76.3% burn a mixture of 78-80% (v/v) gasoline and 22% ethanol (referred to as gasohol), and 17.2% use hydrated ethanol (95% ethanol + 5% water), these data were obtained from the Sao Paulo Environmental Protection Agency. Over the past several years, ambient ozone concentrations in the MASP have reached levels of more than five times that considered protective of public health by the World Health Organization. In the wintertime, ozone levels routinely exceed the 160 ug/m3 hourly Brazilian National Ambient Air-Quality Standard. About 90% of the O3 precursors in the MASP atmosphere are emitted by the vehicle fleet. According to the official state EI of HC (hydrocarbons) emissions from mobile sources, 22% are from gasohol-powered vehicles, 15% from diesel-powered vehicles, 6% from ethanol-powered vehicles and 5% from motorcycles. In addition, a significant contribution to HC emissions comes from evaporative emissions, which constitute 48% of total HC emissions to the atmosphere. In the specific case of nitrogen oxides (NOx), 78% comes from diesel-powered vehicles, 13% from gasohol-powered vehicles, and 4% from ethanol-powered vehicles. One source of uncertainty is the lack of a vehicular emissions inventory (EI). To improve the vehicular EI for the light- and heavy-duty fleet, measurements of vehicle emissions in road tunnels located in the MASP were performed. On March 22-26, 2004 and May 04-07, 2004, respectively, CO, CO2, NOx, SO2, and volatile organic compounds (VOCs) emissions were measured in two tunnels: the Janio Quadros, which carries light-duty vehicles; and the Maria Maluf, which carries light-duty vehicles and heavy-duty diesel trucks. Pollutant concentrations were measured inside the tunnels, and background pollutant concentrations were measured outside of the tunnels. The mean CO and NOx emission factors (in g km-1) were, respectively, 14.6 ± 2.3 and 1.6 ± 0.3 for light-duty vehicles, compared with 20.6 ± 4.7 and 22.3 ± 9.8 for heavy-duty vehicles. The total VOCs emission factor for the Maria Maluf tunnel was 1.4 ± 1.3 g km-1. The main VOCs classes identified were aromatic, alkane, and aldehyde compounds. For the heavy-duty fleet, NOx emission factors were approximately 14 times higher than those found for the light-duty fleet. This was attributed to the high levels of NOx emissions from diesel vehicles. Other important results were related to the identification of the most reactive species for O3 formation using the metrics of MIR potential (Maximum Incremental Reactivity). For São Paulo the more reactive species are the alkenes and aromatics in the O3 formation.
A23C-03 INVITED
An Overview of Air Pollution Problem in Megacities and City Clusters in China
China has experienced the rapid economic growth in last twenty years. City clusters, which consist of one or several mega cities in close vicinity and many satellite cities and towns, are playing a leading role in Chinese economic growth, owing to their collective economic capacity and interdependency. However, accompanying with the economic boom, population growth and increased energy consumption, the air quality has been degrading in the past two decades. Air pollution in those areas is characterized by concurrent occurrence of high concentrations of multiple primary pollutants leading to form complex secondary pollution problem. After decades long efforts to control air pollution, both the government and scientific communities have realized that to control regional scale air pollution, regional efforts are needed. Field experiments covering the regions like Pearl River Delta region and Beijing City with surrounding areas are critical to understand the chemical and physical processes leading to the formation of regional scale air pollution. In order to formulate policy suggestions for air quality attainment during 2008 Beijing Olympic game and to propose objectives of air quality attainment in 2010 in Beijing, CAREBEIJING (Campaigns of Air Quality Research in Beijing and Surrounding Region) was organized by Peking University in 2006 to learn current air pollution situation of the region, and to identify the transport and transformation processes that lead to the impact of the surrounding area on air quality in Beijing. Same as the purpose for understanding the chemical and physical processes happened in regional scale, the fall and summer campaigns in 2004 and 2006 were carried out in Pearl River Delta. More than 16 domestic and foreign institutions were involved in these campaigns. The background, current status, problems, and some results of these campaigns will be introduced in this presentation.
A23C-04
Air Pollution in São Paulo and Santiago de Chile: Sources and Impacts
Urban air pollution is a serious issue for millions in Latin America. São Paulo, Santiago de Chile, México City and many other large urban conglomerates. Fast industrialization, large population growth, emissions from the transportation sectors and many other issues are the cause for the air pollution in these mega cities. São Paulo, with 17 million people, 5.5 million vehicles and strong industry suffers from severe particulate matter and ozone exposure. Santiago de Chile with very unfavorable dispersion characteristics also has problems with PM10 and ozone. Health effects in these areas are a public health concern. In Sao Paulo alone, about 30,000 excess deaths are attributable to air pollution issues. There are also critical institutional issues in the São Paulo metropolitan area, which has 39 municipalities, as well as three other metropolitan areas within a 100-km radius. In Santiago de Chile, a dry climate makes ressuspended soil dust an important PM10 component, and vehicle emissions produces high concentration of secondary organic aerosols. Old diesel buses make black carbon concentrations very high in Santiago. We carried out extensive aerosol source apportionment studies for several years, using PIXE as trace element analysis technique and multivariate statistical analysis to separate and quantify aerosol sources in Santiago and Sao Paulo. We will present results from 5 years studies in both Santiago and Sao Paulo. Vehicles and soil dust dominates the picture, with a strong sulfate component in Santiago de Chile.
A23C-05
Radical production in the near field chemical regime during MILAGRO
A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area. During MILAGRO an extensive set of measurements was collected at T0 (MCMA-2006) to quantify time resolved ROx (sum of OH, HO2, RO2) radical production from the photolysis of nitrous acid (HONO), formaldehyde (HCHO), glyoxal (CHOCHO), ozone (O3), acetaldehyde (CH3CHO), acetone (CH3COCH3). Respective photolysis-frequencies (J-values) were measured by spectroradiometry at ground-level. The Master Chemical Mechanism (MCMv3.1) is employed to calculate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e. taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals). Quasi-simultaneous observations of HONO, HCHO and CHOCHO concentrations at ground-level (by open-path DOAS) and total vertical columns (by MAX-DOAS) enable the assessments of the vertical structure of radical production. Further, the total vertical column measurements enable a comparison with aircrafts intercepting the same airmass. The radical production during MILAGRO-2006 is compared MCMA-2003, which was held three years earlier in a different location of Mexico City. Further, a comparison of Mexico City with Milano, Chelmsford (near London), Birmingham, Pabstthum (near Berlin), and Nashville reveals differences in the magnitude and the timing of radical production. Since the photochemical processing of pollutants is radical limited in Mexico City, our analysis identifies the drivers for such processing. Opportunities are identified for effective air quality controls to reduce peak concentrations of secondary pollutants like O3 and secondary organic aerosol (SOA). Our measurements and analysis comprise a database that enables testing of the representation of radical sources in photochemical models.