A32A-01
Nocturnal Lagrangian Transport of Industrial Plumes from a US Megacity
A Twin Otter research aircraft equipped with a suite of instruments measuring O3, NOx, and volatile organic compounds (VOCs) in conjunction with an altitude controlled balloon (tetroon) was used to investigate nocturnal transport of industrial plumes from the Houston metropolitan area during the 2005 Southeast Texas Tetroon Study (SETTS). Polluted air masses with elevated O3, CO, and NOx along with elevated mass peaks characteristic of industrial VOCs detected by a proton transfer reaction-mass spectrometer (PTR-MS) were tracked from the Houston metropolitan area to remote locations over distances as far as 200 miles. In addition, high levels of biogenic isoprene and its oxidation products such methyl vinyl ketone and methacrolein were detected outside of the polluted plumes. The measurements revealed efficient nocturnal transport of highly reactive VOCs, particularly light alkenes and their oxidation products from the industrial sources, which needs to be considered when assessing the regional effects of a major metropolitan/industrial urban center.
A32A-02
Regional and Local Influences on Surface O3 over Beijing: Constraints from Integrated Surface observations and Modeling
Beijing, the Chinese capital, faces the challenge of improving its atmospheric environment while seeing an annual growth rate of 15% in the number of personal vehicles on the road. Among many pollutants, surface ozone is of particular concern for Beijing as it will host the "green" Olympics Games in summer 2008. Continuous measurements of surface O3 and CO at Miyun (a rural site 50km northeast of Beijing) in 2006 are analyzed using a 3-dimensional chemical transport model (GEOS-Chem) to improve our understanding of regional and local factors contributing to changes in tropospheric O3 in the Beijing area. The location of the site was selected to sample both clean continental air and pollution included in the plume from Beijing. To our knowledge, this is the first station in mainland China providing continuous measurements of O3 and related species (CO and CO2) over a relatively long period (years). Observations show that O3 peaks in June and September, while CO has a broad maximum in winter. Using updated emissions for China, the model successfully reproduces the seasonal variability in O3, CO, and their correlations observed at Miyun. Regional O3 levels representative of north China are identified from observations using concurrent measurements of CO. Events with daytime peak O3 concentrations exceeding 100 ppb were observed mainly in summer (JJA) and in September. A major discrepancy of the model is an overestimate of O3 in July. Observations show a decrease of 16 ppb in mean (median) O3 from June to July, presumably associated with enhanced precipitation and cloudiness in July. Implications of high levels of O3 for crop production will be discussed.
A32A-03
Study on Sources of Volatile Organic Compounds (CMB) in Pearl River Delta region, China
The profiles of major Volatile organic compounds (VOCs) sources including vehicle exhaust, gasoline vapor, painting, asphalt, liquefied petroleum gas (LPG), biomass burning and petrochemical industry in Pearl River Delta were experimentally determined. Source samples were taken by using dilution chamber for mobile and stationary sources, laboratory simulation for biomass burning. The concentrations of 108 VOC species of sources were quantified by using canister with pre-concentration-GC/MS system, from which 52 PAMS hydrocarbons and one kind of chlorinated hydrocarbon were deployed to build the source profiles for source apportionment of VOCs. Based the measurement of source profiles, the possible tracers for various emission sources were identified, e.g 2-methylbutane and 1,3-butadiene were the tracers for motor vehicle exhaust, the characteristic compounds of architectural and furnishing coatings are aromatics such as toluene and m/p-xylene; the light hydrocarbons, namely n-butane, trans-2-butene and n-pentane, dominated the composition of gasoline vapor; and the nonane, decane and undecane are found to represent the asphalt emissions etc.. The CMB receptor model was applied to source apportionment of 58 hydrocarbons measured at seven sites during the PRD campaign, 2004. The 12 kinds of VOC sources include gasoline/diesel-powered vehicle exhaust, gasoline/diesel headspace vapor, vehicle evaporative emissions, liquid petroleum gas (LPG) leakage, painting vapors, asphalt emission from paved road, biomass burning, coal burning, chemical industry and petroleum refinery. Vehicle exhaust was the largest sources contributing over half of the ambient VOCs at the three urban sites (GuangZhou, FoShan and ZhongShan). LPG leakage played an important role with the percentage of 8- 16% in most sites in PRD. Contributions from solvents usage were highest at DongGuan, an industrial site. At XinKen, the solvents and coatings had the largest percentage of 31% probably due to the influence of its upwind area of DongGuan. The local biomass burning was also found to be a noticeable source at XK.
A32A-04
Spatial Variability and a Quality Assurance Check of VOC Measurements During MILAGRO
We present the results of a quality assurance check of volatile organic compound (VOC) measurements made at the T0 urban site during the MILAGRO-2006 field campaign in Mexico City. We focus on a comparison of point- sampling methods and continuous-sampling methods: VOC canisters were collected and co-located with measurements by Proton Transfer Mass Spectrometry (PTR-MS), Fourier-Transform Infrared Spectroscopy (FTIR), and Differential Optical Absorption Spectroscopy (DOAS). Further, we compare point-sampling with open- path DOAS measurements over two light paths (250 m and 1026 m) to investigate spatial gradients of aromatic VOC, including toluene, benzene, and xylenes. We also compare measurements from MILAGRO-2006 with a similar set of measurements that were made during MCMA-2003. Characterizing the VOC speciation and conducting the quality assurance check is a valuable first-step towards constructing a detailed chemical box model to assess the oxidative capacity of the atmosphere during MILAGRO-2006.
A32A-05
Measurements of Nitric Acid (HNO3) during 06 MILAGRO Campaign
Nitric acid (HNO3) represents an important end product of photochemical oxidation and contributes significantly to the problem of acid deposition in the urban and regional atmospheres. Formation of nitric acid occurs from the termolecular reaction between OH and NO2 during the daytime, and from the hydrolysis of N2O5 during the nighttime. Measurements of HNO3 during the MILAGRO Campaign at the T0 site using ion drift-chemical ionization mass spectrometry (ID-CIMS) will be presented and compared with those collected at T0 using complementary techniques and with model simulations using WRF-CHEM. The implications of HNO3 measurements on photochemistry in Mexico City will be discussed.
A32A-06
Insights Into Mega-City Ozone Pollution From the IONS (INTEX Ozonesonde Network Study, 2004 and 2006) Ozonesonde Network
We have used ozone and radiosonde profile data from strategically designed networks (IONS-04, IONS-06; SHADOZ) for better interpretation of atmospheric chemistry and dynamics in the tropics, sub-tropics and mid- latitudes and in critical regions: the urban boundary layer, at the tropopause, free troposphere and at urban-non- urban interfaces. A consistent finding from mega-city regions is how variable ozone is throughout boundary layer and free troposphere - within individual soundings and at a given site over a 3-4 -week campaign. The variability is due to complex interactions between meteorological and chemical factors and between natural and anthropogenic contributions to the ozone budget. Stratospheric influences and lightning influences in the free troposphere are robust. The variability is illustrated by Mexico City ozone soundings trajectories and tracers during INTEX-B (Intercontinental Transport Experiment - 2006) and Milagro/MIRAGE-Mex (Megacity Impacts of Regional and Global Environments) and by Houston, Hunstville, suburban Washington DC (Beltsville, Maryland) and Narragansett in IONS-04 and IONS-06. Trans-boundary pollution within mega-cities (eg. Washington to Boston corridor, Mexico City), is mediated by phenomena like the low-level jet and terrain impacts. Images of the soundings and meteorological information for IONS are at http:croc.gsfc.nasa.gov/intex/ions; http:croc.gsfc.nasa.gov/intexb/ions06.
A32A-07
Analysis of the Mexico City Urban Plume at Altzomoni Site at 4.000 m a.s.l.
Within the scope of the ALTZOMONI campaign in March 2006 it was possible to sample various times the urban plume of Mexico City at a site located at about 4000 m a.s.l. and approximately 60 km to the southeast of the city. Continuous GC-ECD measurements of peroxiacetic nitric anhydride (PAN) and peroxipropionic nitric anhydride (PPN) were used to determine the pollution plume events. High PAN and PPN levels usually coincided with higher CO levels and slightly enhanced O3 values as determined by FTIR. Aerosol Mass Spectrometer results show that, overall, organic aerosols correlate well with PANs. However, some individual PAN peaks are also accompanied by higher aerosol fractions of NO3 and SO4. The results indicate that polluted air masses are present at high altitudes over the Mexico City basin and may likely have a long-range effect. This is in particular true for PAN and PPN. Maximum values up to 2.84 ppbv for PAN and 570 pptv for PPN were observed, which are remarkably high values for almost mid-tropospheric conditions. Together with considerable long lifetimes in the range of weeks at this altitude PAN may serve efficiently as a reservoir species for NO2.
A32A-08
Evolution of trace gas concentrations and the chemical properties of particles at the top of the Mexico City boundary layer.
The Altzomoni ridge is located in the Cortez Pass, in a national park, between the volcanoes of Iztaccíhuatl and Popocatépetl, at an altitude of 4010 m, and 60 km to the SE of the center of Mexico City. This region is isolated from local emissions from combustion yet there is a daily incursion of pollution from either the Mexico City basin, when winds are from the west or from the Puebla valley when winds are from the east. This was the motivation for setting up instruments at this site to measure the concentrations of trace gases and the physical, chemical and optical properties of aerosol particles. Measurements were begun during the last week of November, 2005 and continued until early June, 2006. The concentrations of CN, CO2 and CO clearly indicate that the site is in the free troposphere at night and early morning, but the regional boundary layer grows to altitudes above the site every day. Hence, this site is ideal for making observations of atmospheric chemistry at the interface between rural and urban regions. The preliminary analyses have shown that the "free tropospheric" values of CN, particle bound polycyclic aromatic hydrocarbons (PPAH) and black carbon (BC) rarely decrease below 1000 cm-3, 4 ng m-3, 100 ng m-3, respectively, suggesting the presence of a residual layer of contaminants. Nighttime CO and O3 are usually above 0.1 and 0.05 ppm. The CO concentration at the measurement site is a tenth of the Mexico City value and reached its maximum approximately six hours after the maximum in the city center. The maximum O3 in Mexico City and Altzomoni are frequently the same concentration but with no repeatable pattern in the phase differences. The highly linear relationship between BC and CO reflects the removal and dilution processes, i.e. the average ratio between BC and CO in Mexico City is 1000:1 whereas it is 3000:1 in Altzomoni. This relationship also depends on the origin of the boundary layer air, i.e. whether it comes from the east or west. The relationship between BC and PPAH is also sensitive to air mass origin and reflects secondary processes occurring between the sources and the measurement site.