A31C-01
Emission Sources and Chemical Composition of the Atmosphere of a Mega-city in South Asia
The environmental regulations in the countries in the western hemisphere have greatly decreased the concentrations of PM2.5, black carbon (BC), SO4, SO2, and trace elements. Owing to rapid industrialization, concentrations of many chemical species in South Asia are rising and are expected to continue to increase. The impact of aerosols on global climate and on human health would also increase with time. Therefore, we conducted an extensive campaign to determine PM2.5 mass, concentrations of 25 trace elements, 13 ions, black and organic carbon, acidic gases and NH3 in the mega-cities of Karachi (population, ~14.5 million), and Lahore (population, 10 million), Pakistan. Here we present the data from Lahore. Continuous sampling of PM2.5 (particulate matter of <2.5 µm aerodynamic diameter) and acidic and alkaline gases was carried out in winter (2005-2006) in Lahore which is highly impacted by urban and agricultural emissions but has remained unexplored in terms of atmospheric chemistry. While sampling continued from November 2005 to February 2006, it was possible to collect several samples during fog episodes. A low volume sampler equipped with two inlets was deployed for simultaneous collection of aerosol on quartz and PTFE filters, the latter being coupled to an annular diffusion denuder to collect acidic and alkaline gases. Water soluble ions in denuder gas samples and PM2.5 collected on PTFE filters were analyzed using ion chromatography, trace elements by ICP-MS, and organic and elemental carbon on quartz filters using thermal-optical carbon analyzer. Concentrations of BC were determined every 5 min with an Aethalometer. PM2.5 mass concentration varied an order of magnitude, 53 to 476 μg m-3 (mean, 191 μg m-3). Concentrations of the anthropogenic elements were exceedingly high, as much 100 to 1000 fold of those observed in cities such as New York. Maximum concentrations of BC, OC, Pb, Zn, SO4 2- , NH4+ were 110, 250, 12, 48, 66, and 60 μgm-3, respectively. HONO and NH3 concentrations of up to 25 and 117 ppb were observed. A strong diurnal pattern was evident in the concentration of elemental and organic carbon which was perhaps controlled by variation in mixing heights. We used HYSPLIT4 air trajectories, intercomponent relationships and meteorological observations to explain the sources and the impacts of fog chemistry and mixing heights on atmospheric processing of the chemical constituents. Aerosols collected on this campaign were found to carry the signatures of emissions from Afghanistan, North and Central Pakistan, North India in addition to the local pollution sources. Statistical analysis suggests emissions from coal and oil combustion, industrial processes, building construction sites and biomass burning as the primary emission sources. Carbonaceous aerosols contributed about 69% of the PM2.5 mass. Findings of our study will improve the understanding of the critical roles and interactions between chemical composition and size of atmospheric particles, atmospheric boundary layer and meteorological phenomena that manipulate the chemistry of an urban atmosphere. The results should play a vital role in any strategy to regulate emissions and improve air quality in the region.
A31C-02
Flux Emissions of SO2 and NO2 Measured at the Tula Industrial Complex (Mexico) during MCMA 2006 Field Campaign using a Mini-DOAS System
The Tula industrial zone is located 60 km northeast from the Mexico City Metropolitan Area (MCMA), in the Hidalgo State in México. This region is known as the Tula-Vito-Apasco industrial corridor, where a number of industries are located. According to the latest information from the environmental authority, about 313,000 ton/year of SO2 and 40,000 ton/year of NOx are released in this region. The Miguel Hidalgo refinery (MHR) and the Francisco Pérez Ríos power plant (FPRPP) are the main emitters, contributing almost 90% of SO2 and 80% of NOx from the total emission inside the Hidalgo State. Other industries such as cement plants, open-sky mines and agricultural activities are also responsible for important emissions of particulat matter (PM) into the atmosphere and soil erosion. This highly industrialized region is thought to influence the air quality in the MCMA, where in some occasions SO2 concentrations in the north part of the city have exceeded the Mexican air quality standard (130 ppb as a 24 hour average), which could not be attributed to irregular operations of industries located in the surrounding area. To address the question of emissions from the refinery and the power plant, the total fluxes of SO2 and NO2 were determined by measurements of their respective integrated vertical column in the neighborhood of the Tula industrial zone, using a Mini-DOAS system. These measurements were carried out as part of the MCMA-2006/MILAGRO Field Campaign, from March 24th to April 18th 2006. Meteorological measurements at the height of the plume dispersion were also determined using pilot balloons and radiosondes techniques. The experimental data were complemented by model simulations. Forward Lagrangian stochastic trajectories were calculated to simulate the plume using FLEXPART in combination with meso-scale meteorological simulations with MM5. The experimental data set was used to evaluate model performance. The simulations were used as an additional estimate of plume transport speeds. Potential air quality impacts on the MCMA were simulated. These were verified by combining surface SO2 measurements in the basin with backward trajectories, thereby providing a means of discriminating the urban impacts of different potential source regions.
A31C-03
Flux Measurements of Trace Gases, Aerosols and Energy from the Urban Core of Mexico City
As part of the MILAGRO field campaign in March 2006 we deployed a flux system in a busy district of Mexico City surrounded by congested avenues. The flux system consisted of a tall tower instrumented with fast-response sensors coupled with eddy covariance (EC) techniques to measure fluxes of volatile organic compounds (VOCs), CO2, CO, aerosols and energy. The measured fluxes represent direct measurements of emissions that include all major and minor emission sources from a typical residential and commercial district. In a previous study we demonstrated that the EC techniques are valuable tools to evaluate emissions inventories in urban areas, and understand better the atmospheric chemistry and the role that megacities play in global change. We measured fluxes of olefins using a Fast Olefin Sensor (FOS) and the EC technique, fluxes of aromatic and oxygenated VOCs by Proton Transfer Reaction-Mass Spectroscopy (PTR-MS) and the disjunct eddy covariance (DEC) technique, fluxes of CO2 and H2O with an open path Infrared Gas Analyzer (IRGA) and the EC technique, fluxes of CO using a modified gradient method and a commercial CO instrument, and fluxes of aerosols (organics, nitrates and sulfates) using an Aerodyne Aerosol Mass Spectrometer (AMS) and the EC technique. In addition we used a disjunct eddy accumulation (DEA) system to extend the number of VOCs. This system collected whole air samples as function of the direction of the vertical wind component, and the samples were analyzed on site using gas chromatography / flame ionization detection (GC-FID). We also measured fluxes of sensible and latent heat by EC and the radiation components with a net radiometer. Overall, these flux measurements confirm the results of our previous flux measurements in Mexico City in terms of the magnitude, composition, and distribution. We found that the urban surface is a net source of CO2 and VOCs. The diurnal patterns show clear anthropogenic signatures, with important contributions from vehicular traffic. The DEA results for individual hydrocarbons show that the alkane fluxes are considerably higher than alkene fluxes, which is consistent with ambient concentration measurements and with the emission inventory for Mexico City. CO fluxes, estimated from a modified gradient technique, were more than 10% of the measured CO2 fluxes (on a molar basis) which is much higher than is generally expected for combustion efficiencies in mobile and other sources. Investigation of this result is underway. The energy balance distribution and radiative parameters observed are similar to distributions and parameters reported for other urban sites.
A31C-04
Improving emissions inventories in Mexico through systematic analysis of model performance along C-130 and DC-8 flight tracks during MILAGRO
During the MILAGRO campaign in March 2006 the University of Iowa provided regional air quality forecasting for scientific flight planning for the C-130 and DC-8. Model performance showed positive bias of ozone prediction (~15ppbv), associated to overpredictions in precursor concentrations (~2.15 ppbv NOy and ~1ppmv ARO1). Model bias showed a distinct geographical pattern in which the higher values were in and near Mexico City. Newer runs in which NOx and VOC emissions were decreased improved ozone prediction, decreasing bias and increasing model correlation, at the same time reducing regional bias over Mexico. This work will evaluate model performance using the newly published Mexico National Emissions Inventory, and the introduction of data assimilation to recover emissions scaling factors to optimize model performance. Finally the results of sensitivity runs showing the regional impact of Mexico City emissions on ozone concentrations will be shown, along with the influence of Mexico City aerosol concentrations on regional photochemistry.
A31C-05
VOCs Speciation From Steam Boiler Stacks of Industries Located in Naucalpan
Results of VOCs speciation from industrial steam boiler stacks located in Naucalpan are presented and discussed. This municipality is located north of the Metropolitan Zone of the Valley of Mexico (MZVM). Speciation of VOCs is important to generate information about sources of pollution, to update emission inventories, to study the dynamics of pollutants in the atmosphere, and to estimate possible risks of population exposure. This information is valuable for decision making on air pollution control strategies. Samples from 35 steam boilers form industries burning Diesel, LPG, or CNG were taken using the US-EPA Method 18. Selected samples from the use of different fuels were analyzed using gas chromatography and flame ionization detection (GC-FID) according to US-EPA protocol TO-14. The VOCs analyzed included alkanes of 9 carbons or less, alkenes of 7 carbons or less and aromatics (families of benzene). The results show consistency on the VOCs detected on Diesel samples. The main compounds found were 1- Butene+iButylene, m/p-Xylene, Ethane, Propene, Propane, Acetylene, 2Me-1Butene, and Toluene. The average concentrations of these compounds were in the range of 130 to 385 ppbC. The results of LPG samples did not show a definite pattern of VOCs, although light components predominate and, in some samples, Toluene and Xylene. These last components were not expected for industries reporting the use of LPG, perhaps due to the use of a combination of fuels and mistakes in the reports of fuel used at the time of sampling. The analysis of CNG samples show predominance of light VOCs, in the range of 90 to 300 ppbC. As in the case of LPG, some aromatics showed high concentrations in some samples analyzed perhaps due to the use of different fuels in the boiler. The results of this study are the first results of VOCs speciation obtained form exhaust gases from stacks of Mexican industries. The data reported are valuable to analyze emission inventories of VOCs and to better understand the dynamics of pollutants in the MZVM.
A31C-06
OH and H2SO4 observations during MIRAGE/IMPEX
The MIRAGE/IMPEX program provided a unique opportunity to observe OH within a variety of environments ranging from a large urban mega-city, rural farmland, to the marine. Depending on the SO2 concentration, OH can produce various amounts of H2SO4 within these environments, leading to aerosol formation and growth. Measured OH and H2SO4 concentrations from the MIRAGE/IMPEX study will be presented including some of the largest ambient H2SO4 concentrations observed by our group. Comparisons of model simulated OH will also be presented.
A31C-07
Hydrogen Cycle in a Megacity: Diurnal Variation, Holiday Effect and Source Fingerprinting
Mexico City with a population of 25 million, the largest mega-city in North America, provides a testing ground for
regional and global impacts on air quality and climate of increasing urbanization. To help understand the
biogeochemistry of Mexico City a comprehensive international multi-agency Megacity Initiative: Impact on
Regional and Global Environment (MILAGRO) field campaign was conducted in March 2006. We report diurnal
and weekly observations of molecular hydrogen, CO, and CO2 in Mexico City. A regular diurnal profile with
peak concentrations of hydrogen in early morning caused by the high traffic and shallow boundary layer was
revealed. A record level of hydrogen of 5 ppm, a factor of 10 above background levels, was measured. We
hypothesize that most of the hydrogen is coming from automobiles. However, we did observe emissions from
other industrial or power plant sources. Analysis of the H2/CO, CO/CO2, and H2/CO2 ratios
are developed as a chemical fingerprinting method to delineate these sources and relate them to combustion
efficiency. We utilize H2/CO ratios to diagnose traffic patterns, for example the early morning H2/CO
peak is attributed to sluggish rush our traffic. We also observe significantly (25%) lower hydrogen during the
weekend holidays than workdays. Finally, regional scale modeling of the Mexico City hydrogen cycle is performed
using the Weather Research Forecast: Chemistry (WRF-CHM) model at 1 km resolution. The model results are
compared to our measurements to gain a quantitative understanding of hydrogen sources and sinks in Mexico
City. Our findings are significant to the understanding of the global hydrogen cycle and developing an urban
baseline for hydrogen to assess potential perturbations to it from transitioning to a hydrogen economy.
http:aerosols.lanl.gov
A31C-08
Automatic Monitoring of Criteria Pollutants and Meteorological Parameters in Boundary Sites of Mexico City under QA/QC Standards
MILAGRO, an extensive air quality monitoring campaign, was conducted in the Mexico City Metropolitan Area
(MCMA) during March 2006, in order to assess the air pollutants transport and their influence at regional and
global scales.
In support of this campaign a number of criteria pollutants and meteorological parameters measurements were
conducted in boundary sites of the MCMA in order to determine the surface conditions in these transition sites.
The boundary sites were selected based on results from previous studies, information provided systematically by
the Mexico City Ambient Air Monitoring Network (Sistema de Monitoreo Atmosférico, SIMAT), pollutants trends
and meteorological and climatic factors that participate in the dispersion and transport under different ventilation
scenarios. Seven mobile units and two fixed stations were deployed for the continuous determination of criteria
pollutants and meteorological parameters. In order to warranty the pollutants concentrations measurements'
quality and comparability, calibrations and verifications were implemented at the designated monitoring sites.
Data had been analyzed with statistical tools and comparisons were made against nearby SIMAT stations.
Several interesting conclusions were achieved.
http:www.mce2.org/