Atmospheric Environment (v.39, #37)

Sampling artifact estimates for alkanes, hopanes, and aliphatic carboxylic acids by Tanasri Sihabut; Joshua Ray; Amanda Northcross; Stephen R. McDow (6945-6956).
Sampling artifacts for molecular markers from organic speciation of particulate matter were investigated by analyzing forty-one samples collected in Philadelphia as a part of the Northeast Oxidant and Particulate Study (NEOPS). Samples were collected using a high volume sampler with two quartz fiber filters in series. n-Alkanes (C23–C31), hopanes (C27–C31), and n-alkanoic acids (C10–C22) were analyzed by gas chromatography-mass spectrometry (GCMS). The extent of artifact error was dependent on vapor pressure and species concentration. Particulate organic species are classified into the following three categories: (1) the amount collected on the backup filter was often a large fraction of the amount collected on the front filters (n-alkanes C23 and C24, n-carboxylic acids C10–C14); (2) the amount collected on the backup filter was consistently a small fraction of the amount collected on the front filter (n-alkanes C25–C28, hopanes C27–C30, n-carboxylic acids C15–C18, and dicarboxylic acids C3–C9); (3) the species was rarely observed on backup filters (n-alkanes C29–C31, hopanes C31 and C32).
Keywords: Organic aerosol; Sampling artifact; GCMS; n-alkanes; Hopanes; Carboxylic acids;

Fully coupled “online” chemistry within the WRF model by Georg A. Grell; Steven E. Peckham; Rainer Schmitz; Stuart A. McKeen; Gregory Frost; William C. Skamarock; Brian Eder (6957-6975).
A fully coupled “online” Weather Research and Forecasting/Chemistry (WRF/Chem) model has been developed. The air quality component of the model is fully consistent with the meteorological component; both components use the same transport scheme (mass and scalar preserving), the same grid (horizontal and vertical components), and the same physics schemes for subgrid-scale transport. The components also use the same timestep, hence no temporal interpolation is needed. The chemistry package consists of dry deposition (“flux-resistance” method), biogenic emission as in [Simpson et al., 1995. Journal of Geophysical Research 100D, 22875–22890; Guenther et al., 1994. Atmospheric Environment 28, 1197–1210], the chemical mechanism from RADM2, a complex photolysis scheme (Madronich scheme coupled with hydrometeors), and a state of the art aerosol module (MADE/SORGAM aerosol parameterization).The WRF/Chem model is statistically evaluated and compared to MM5/Chem and to detailed photochemical data collected during the summer 2002 NEAQS field study. It is shown that the WRF/Chem model is statistically better skilled in forecasting O3 than MM5/Chem, with no appreciable differences between models in terms of bias with the observations. Furthermore, the WRF/Chem model consistently exhibits better skill at forecasting the O3 precursors CO and NO y at all of the surface sites. However, the WRF/Chem model biases of these precursors and of other gas-phase species are persistently higher than for MM5/Chem, and are most often biased high compared to observations. Finally, we show that the impact of other basic model assumptions on these same statistics can be much larger than the differences caused by model differences. An example showing the sensitivity of various statistical measures with respect to the treatment of biogenic volatile organic compounds emissions illustrates this impact.
Keywords: Urban and regional pollution; Urban and regional air quality modeling; Air quality forecasting; Aerosols and particles;

Global warming potential of manure amended soils under rice–wheat system in the Indo-Gangetic plains by A. Bhatia; H. Pathak; N. Jain; P.K. Singh; A.K. Singh (6976-6984).
Use of organic amendments such as farmyard manure (FYM), green manure (GM) and crop residues is important to improve soil health and reduce the dependence on synthetic chemical fertilizer. However, these organic amendments also effect the emissions of greenhouse gas (GHG) from soil. Influence of different organic amendments on emissions of GHG from soil and their global warming potential (GWP) was studied in a field experiment in rice–wheat cropping system of Indo-Gangetic plains (IGP). There was 28% increase in CH4 emissions on addition of 25% N through Sesbania GM along with urea compared to urea alone. Substitution of 100% inorganic N by organic sources lead to a 60% increase in CH4 emissions. The carbon equivalent emission from rice–wheat systems varied between 3816 and 4886 kg C equivalent ha−1 depending upon fertilizer and organic amendment. GWP of rice–wheat system increased by 28% on full substitution of organic N by chemical N. However, the C efficiency ratios of the GM and crop residue treatments were at par with the recommended inorganic fertilizer treatment. Thus use of organic amendments along with inorganic fertilizer increases the GWP of the rice–wheat system but may improve the soil fertility status without adversely affecting the C efficiency ratio. However, the trade-off between improved yield and soil health versus GHG emissions should be taken into account while promoting the practice of farming with organic residues substitution for mineral fertilizer.
Keywords: Carbon equivalent emission; Carbon dioxide; Methane; Nitrous oxide; Greenhouse gas;

Contribution of unburned lubricating oil and diesel fuel to particulate emission from passenger cars by Sandro Brandenberger; Martin Mohr; Koni Grob; Hans Peter Neukom (6985-6994).
In this study we determined particle-bound paraffins in the exhaust of six light-duty diesel vehicles on a chassis dynamometer for different driving cycles and ambient temperatures. The filters containing particulate matter were extracted with dichloromethane in a Soxhlet apparatus, and the paraffin analysis was performed using two-dimensional normal phase high-pressure liquid chromatography (HPLC) coupled on-line to gas chromatography-flame ionization detection (GC–FID). The different molecular mass of lubricant and diesel paraffins facilitated the distinction between diesel and lubricant contribution to the emission. Although all vehicles were certified according to the same emission class, there were considerable variations between vehicles. The study showed that under cold-start conditions the organic mass fraction ranged from 10% to 30% with respect to particle mass and the paraffins from 30% to 60% with respect to the organic mass. With cold engine, falling ambient temperature increased the emission of unburned diesel fuel, whereas that from unburned lubricating oil was less affected. Under warm-start conditions, the ambient temperature had less impact on the emission of paraffins. The emissions were also affected by the operating conditions of the engine: driving cycles with higher mean load tend towards higher emissions of lubricant. The operating conditions also affected the distribution of paraffins: the emission of light paraffins seemed to be lower with higher load in the driving cycle. With an urban and a highway cycle, roughly 40% and 80% w/w, respectively, of unburned paraffins were contributed by the lubricant. Measurements of polycyclic aromatic hydrocarbons (PAH) in lubricating oil showed lubricant to be a sink for PAHs. As lubricant significantly contributes to the organic emission, as shown in this study, it can be assumed that it is also a significant source of PAH emissions.
Keywords: Diesel exhaust; Particulates; Paraffins; Driving cycles; PAH; Lubricating oil;

Seasonal variations and interactions of N-containing gases and particles over a coniferous forest, Saxony, Germany by Kirsten Plessow; Gerald Spindler; Frank Zimmermann; Jörg Matschullat (6995-7007).
Ambient concentrations of NH3, HNO3, HNO2, HCl, SO2, particulate NH 4 + , NO 3 - , and SO 4 2 - were simultaneously measured from October 2001 to April 2003 at the Oberbärenburg research site (Erzgebirge, Germany). Seasonal variations of gas phase concentrations were often related to meteorological parameters and specific source strength. The particulate species (PM2.5) displayed weak seasonal trends, but periods with low mixing heights resulted in significantly elevated concentrations.Mean NH3, HNO2, HNO3, and SO2 concentrations in air (μg m−3) were about 0.48, 0.30, 0.80, and 5.9, respectively. With a PM2.5-mass fraction of 11.3 μg m−3, the Erzgebirge was moderately polluted. Average particle bound NH 4 + - (1.5 μg m−3) and NO 3 - - (2.2 μg m−3) concentrations were 2–3-times higher than the corresponding gas phase concentrations. In summer, preferentially (NH4)2SO4 existed, while the dominance of NH4NO3-aerosol increased in spring. The thermodynamic equilibrium constant for the system NH3/HNO3/NH4NO3 agrees well with the measured concentration product considering the co-existence of SO 4 2 - . The particulate phase is often favoured under ambient temperature and humidity.Nearly all species exhibited maximum concentrations from February to April 2003, during a stable high-pressure system. In March and April 2003, the secondary ions contributed more than 90% to the PM2.5 fraction. This was particularly due to increased NO 3 - - concentrations. The formation of NO 3 - was supported by a large supply of free NH3.
Keywords: Ammonia; Nitric acid; Nitrate; Soluble ions; PM2.5; Honeycomb denuder; Filter-pack;

Aspects of ozone transport, mixing, and chemistry in the greater Maryland area by Fred M. Vukovich; James Scarborough (7008-7019).
This study examined the role of ozone transported and the subsequent mixing of the transported ozone on the ozone concentration and chemistry in the surface layer at locations in central Maryland. Surface data from the United States Environmental Protection Agency's (EPA) Aerometric Information Retrieval System (AIRS) database, ozone profile data from the University of Maryland's aircraft measurements, trajectory analyses using the HYSPLIT model, and predictions using the Semi-Empirical Integrated Pollution Model (SIPM) for the periods 11–15 July 1995 and 12–16 July 1997 were used to meet the objectives of this study. It was found that on the day before the air mass reached the receptor in Maryland, the air mass passed over regions where the diurnal maximum ozone concentration was sufficiently large and the mixing sufficiently deep, in most cases, to have been the primary source of the ozone that was found over central Maryland the next morning. Mixing took place between the air mass above the nocturnal inversion and the surface layer when the nocturnal inversion broke down sometime after sunrise, and the ozone in the surface layer increased by about 13 ppb, on average, as a result of the mixing. The results also showed that when certain conditions were met, the chemistry in the surface layer produced up to about three times more ozone when mixing of ozone into the surface layer took place and when a non-zero value for the diurnal minimum zone concentrations were used to initialize the chemistry. There were, however, a number of situations when mixing of ozone into the surface layer and when a non-zero value for the diurnal minimum ozone concentrations were used to initialize the chemistry, had little effect on the surface ozone layer. The conditions, under which both situations occurred, are discussed.
Keywords: Boundary layer ozone; Ozone transport; Ozone precursors; Boundary layer ozone chemistry;

Six dust episodes were observed in Beijing in 2002. Both TSP (Total Suspended Particulate, particle size smaller than 100 μm) and PM2.5 (particle size smaller than 2.5 μm) aerosol samples in these episodes were collected and their characteristics of water-soluble part were elaborated in demonstrating the mixing of mineral aerosol with pollution aerosol in the long-range transport of Asia aerosols with various sources and different paths. The dust storm peaked on 20 March, in which the highest concentrations of TSP and PM2.5 were 10.9 and 1.4 mg m−3, respectively. The mass fraction of water-soluble part generally decreased with the increase of dust intensity. SO4 2− contributed 38–70% to the total anions and Ca2+ contributed 37–80% to the total cations, indicating that SO4 2− and Ca2+ were the most abundant anion and cation, respectively. The major ions of the water-soluble parts could be classified into three groups, i.e., the crust ions (Ca2+, Na+, and Mg2+), the pollution-crust ions (SO4 2−, Cl, and K+), and the pollution ions (NO3 , NH4 +, NO2 , and F). Crust ions and pollution ions were the main ion fractions in super dust and non-dust days, respectively, whereas the pollution-crust ions were the main ion fractions in both dust days of various dust intensity and non-dust days, which demonstrated clearly that the mixing between mineral and pollution aerosols was ubiquitous during the dust seasons (even in the super dust storm days) although it was more obvious in those normal and weak dust episodes. The main chemical species of the water-soluble part of the aerosols were CaCO3 in the super dust storm, CaSO4 in the normal and the weak dust events, and NH4NO3 in the non-dust event days. The secondary transformation of sulfate and nitrate occurred on dust particles both during and after dust days provided the strong evidence of the mixing between mineral and pollution aerosols during the long-range transport of dust.
Keywords: Dust aerosols; Composition; Speciation; Secondary transformation;

Estimation of contributions of NO2 and PAN to total atmospheric deposition of oxidized nitrogen across Eastern Canada by Leiming Zhang; Jeffrey R. Brook; Robert Vet; Allan Wiebe; Cristian Mihele; Mike Shaw; Jason M. O’Brien; Syed Iqbal (7030-7043).
Total oxidized nitrogen (N) dry deposition fluxes have been estimated for a 1-year period at seven eastern Canadian rural sites using observed air concentrations of nitric acid (HNO3) and particle nitrate (NO3 ), modelled air concentrations of nitrogen dioxide (NO2) and peroxyacetyl nitrate (PAN), and modelled dry deposition velocities. The calculated annual dry N deposition fluxes range from 0.8 to 4 kg N ha−1 depending on location. HNO3 is estimated to contribute at most 47–68% of the total, while conservative estimates for NO2 indicate it contributes 12–36% of the total. Smaller contributions are from NO3 (12–20%) and PAN (3–16%). The NO2 contribution to total N dry deposition is higher at locations closer to NO x emission sources (e.g., over and downwind of urban areas) than that at remote locations. Available rural NO2 measurements indicate that the modelled NO2 concentrations (from which dry deposition of NO2 is calculated) are low. With adjustments for this bias, the NO2 contribution to total dry N flux can be higher than 50%, implying that NO2 dry deposition is more important over a greater land area than previously believed and likely more important than HNO3 over some areas.Combining our calculated dry deposition totals with monitored wet deposition produces an estimate of total annual N deposition ranging from 3 to 8 kg N ha−1, depending on location, with 25–60% contributed by dry deposition. If NO2 and PAN dry deposition are excluded, then total N deposition is underestimated by 7–30%, depending on location, suggesting that previous estimates that have not included NO2 have underestimated dry and total N deposition substantially.
Keywords: Dry deposition; Wet deposition; Modelling and measurement; Oxidized nitrogen;

Evaluation of a Eulerian and Lagrangian air quality model using perfluorocarbon tracers released in Texas for the BRAVO haze study by Bret A. Schichtel; Michael G. Barna; Kristi A. Gebhart; William C. Malm (7044-7062).
The Big Bend Regional Aerosol and Visibility Observational (BRAVO) study was designed to determine the sources of haze at Big Bend National Park, Texas, using a combination of source and receptor models. BRAVO included an intensive monitoring campaign from July to October 1999 that included the release of perfluorocarbon tracers from four locations at distances 230–750 km from Big Bend and measured at 24 sites. The tracer measurements near Big Bend were used to evaluate the dispersion mechanisms in the REMSAD Eulerian model and the CAPITA Monte Carlo (CMC) Lagrangian model used in BRAVO. Both models used 36 km MM5 wind fields as input. The CMC model also used a combination of routinely available 80 and 190 km wind fields from the National Weather Service's National Centers for Environmental Prediction (NCEP) as input. A model's performance is limited by inherent uncertainties due to errors in the tracer concentrations and a model's inability to simulate sub-resolution variability. A range in the inherent uncertainty was estimated by comparing tracer data at nearby monitoring sites. It was found that the REMSAD and CMC models, using the MM5 wind field, produced performance statistics generally within this inherent uncertainty. The CMC simulation using the NCEP wind fields could reproduce the timing of tracer impacts at Big Bend, but not the concentration values, due to a systematic underestimation. It appears that the underestimation was partly due to excessive vertical dilution from high mixing depths. The model simulations were more sensitive to the input wind fields than the models’ different dispersion mechanisms. Comparisons of REMSAD to CMC tracer simulations using the MM5 wind fields had correlations between 0.75 and 0.82, depending on the tracer, but the tracer simulations using the two wind fields in the CMC model had correlations between 0.37 and 0.5.
Keywords: BRAVO; Tracer; Eulerian model; Lagrangian particle dispersion model; Long-range transport;

Among the monoterpenes, d-limonene is one of the most reactive, and has one of the highest particle formation potentials. Chamber experiments with d-limonene, nitric oxide, nitrogen dioxide, and diurnal natural sunlight are compared with simulation results from a first generation semi-explicit d-limonene daytime mechanism. The d-limonene model adequately predicts the timing of NO−NO2 crossover, d-limonene decay, and the general trend of ozone formation, and particle mass accumulation. When experimental secondary organic aerosol (SOA) masses were greater than 1 mg m−3 the simulations tended to agree closely with the measured aerosol maxima. At lower SOA concentrations, the simulations tended to overpredict measured aerosol maxima by 25–50%. FTIR analysis and GC-ECD measurements indicate particle phase nitrates and peroxyacetyl nitrate (PAN) formation in the system. In the afternoon when temperatures are highest in the outdoor chambers, the slow rise of continuous ozone measurements suggests that PAN type compounds were decomposing to “bleed” NO2 into the gas phase. Partitioning calculations also suggest that these types of compounds are off-gassing from the particle phase later in the afternoon as well, and provide an additional source of NO2. Predicted aerosol yields with a commonly used two-parameter aerosol yield model are compared with experimental aerosol yields. The parameritized aerosol yield model had difficulty predicting most of the UNC chamber data. The explicit d-limonene mechanism developed in this study could reasonably simulate the aerosol formation trend in the Caltech chambers, but tended to overpredict SOA maxima.
Keywords: d-Limonene; Kinetics mechanism; Aerosol modeling; SOA; Gas–particle partitioning;

Seasonal variability of optical properties of aerosols in the Eastern Mediterranean by M. Vrekoussis; E. Liakakou; M. Koçak; N. Kubilay; K. Oikonomou; J. Sciare; N. Mihalopoulos (7083-7094).
The aerosol optical properties (scattering and absorption coefficients) were investigated at two remote locations in the Eastern Mediterranean in conjunction with aerosol ion composition measurements: Finokalia in the Crete Island in Greece (March 2001–June 2002) and Erdemli in Turkey (July 1999–June 2000). Ambient light-scattering coefficient (σ sp−532 nm) at Finokalia had a mean value of 50±23 Mm−1 while at Erdemli this value was 90±160 Mm−1, due to a severe dust event that occurred from 17 to 19 April 2000. Scattering coefficients up to 5000 Mm−1 were encountered during the transition periods (spring and autumn) and were associated with dust storm events. During these events significant correlations were observed between dust and σ sp and mass scattering efficiencies of 0.21 and 0.96 m2g−1 were calculated for dust for Finokalia and Erdemli, respectively. Significant correlations were also observed at both locations between non-sea-salt sulphate (nss-SO4 2−); σ sp and mass scattering efficiencies of 5.9±1.8 and 5.7±1.4 m2g−1 were calculated for the nss-SO4 2− at Finokalia and Erdemli, respectively. At Finokalia absorption measurements were also performed at the same time and the mean absorption coefficient (σ ap−565 nm) was found to be 5.6±3.6 Mm−1. Maxima of absorption coefficient were associated with two distinct meteorological situations indicative of pollution transported from northern Europe and Saharan dust events. Saharan dust can therefore significantly contribute to both scattering and absorption of solar radiation, the latter due to its hematite content. Based on scattering and absorption measurements, an annual mean single-scattering albedo (ω) adjusted at 550 nm of 0.89±0.04 was calculated for Finokalia. Finally, radiative forcing efficiency (RFE) over the sea at 550 nm induced by aerosols has been calculated for Finokalia. RFE follows a clear seasonal variation, with the lowest mean values during summer (−73W m−2) and the highest during winter (−30W m2). Using aerosol optical thickness measurements in the area, we obtain radiative forcing estimates at the top of the atmosphere (TOA) ranging from −12.6 to −2.3 W m2 for summer and winter, respectively. These values are up to five times higher than that induced by the greenhouse gases (2.4 Wm−2) but opposite in sign.
Keywords: Optical properties of aerosols; Seasonal variation; Chemical composition; Radiative forcing; Eastern Mediterranean;

Long-term measurements of SO2 dry deposition over Gansu Province, China by Wanquan Ta; Chun Wei; Fahu Chen (7095-7105).
Potassium carbonate sulfation plates, monitored monthly for 11 years from 48 sites in 11 cities in Gansu Province, China, provide a crude estimate of cumulative SO2 dry depositions. Measured SO2 dry deposition rates were 1.6–472 mg m−2  day−1 and had seasonal variations with maxima in winter and minima mainly during summer as a result of higher winter and lower summer SO2 concentrations. The 11-year monthly average SO2 dry deposition rates are 23.2–248.97 and 11.7–175.6 mg m−2  day−1 in the eleven cities in winter and summer, respectively. A monthly average SO2 deposition velocity was also estimated from 0.06 to 9.72 cm s−2 in the 11 cities studied with a 11-year average maximum value of about 1.1–2.7 cm s−2 in April and July and a 11-year average minimum value of about 0.2–1.0 cm s−1 in January. The SO2 dry deposition velocity also exhibits an increasing with wind speed in basins of less than 500 mm annual precipitation. In contrast, due to influences of the relative humidity in valleys of more than 500 mm annual precipitation, it shows a decreasing trend with wind speed increasing.
Keywords: SO2 dry deposition; SO2 concentration; SO2 dry deposition velocity; K2CO3 sulfation plate;

Measurements of ammonia emissions from manure storing and spreading stages in Polish commercial farms by Martin Ferm; Tadeusz Marcinkowski; Marek Kieronczyk; Stefan Pietrzak (7106-7113).
Representative measurements of ammonia volatilisation from manure at storing and spreading stages were carried out during several years in Poland. All measurements were made using passive horizontal flux samplers. The average ammonia emission from manure storage heaps was determined as 11 kg/LU/year corresponding to a quarter of the stored total nitrogen amount. The ammonia emissions were higher in the winter when the temperature difference between the heap and the ambient air was higher. The project is part of the Baltic agriculture run-off action program (BAAP) applied to Poland. One measurement of the ammonia emission from a slurry tank gave a significantly lower emission compared to the commonly used manure storage heap.
Keywords: Ammonia emission; Manure heap; Passive horizontal flux sampler, Poland;

Concentration measurements are reported for particulate organic and elemental carbon, measured using an R&P 5400 ambient particulate carbon monitor at four sites in the United Kingdom: one roadside (London, Marylebone Road), two urban (London, North Kensington, and Belfast, Centre) and one rural (Harwell). The measurements were collected on a continuous three hourly average basis between January 2002 and mid-2004. The concentrations show no obvious seasonal cycle, except for an increase in OC/EC ratio at London, North Kensington, during the summer months consistent with a possibly greater relative contribution of secondary organic aerosol. Perhaps surprisingly this is not, however, seen at the rural Harwell site. At Belfast, both organic and elemental carbon show elevated winter concentrations, consistent with important local primary sources. Only at the roadside Marylebone Road site is there a high correlation ( r 2 = 0.59 ) between organic carbon and elemental carbon concentrations which persists when simultaneously measured urban background concentrations from the nearby North Kensington site are subtracted; the OC/EC ratio in the traffic-related concentration increment is 0.88, well below the ratios typical of the urban background. Directional analysis of the data from the Marylebone Road street canyon shows that whilst elemental carbon concentrations are determined primarily by on-road traffic emissions, both organic carbon and PM10 derive primarily from inputs from outside the street canyon. It therefore appears that at all times of year non-traffic sources of particulate organic carbon, be they primary or secondary, are dominant over traffic emissions in the urban background. Organic compounds account for about 22% of aerosol mass, irrespective of site.
Keywords: Elemental carbon; Organic carbon; Traffic emissions; Urban background; Particulate carbon;

Direct climate forcing due to scattering and absorption of the main aerosol components (ammonium sulfate and total carbon) was estimated seasonally in Hungary by a box model. Ammonium sulfate played an important role in the direct forcing while the carbonaceous aerosol contributed significantly to the development of extinction. In summer, the scattering effect of both species showed a maximum (ammonium sulfate: −2.21±1.73 W m−2, total carbon: −0.88±0.73 W m−2), while the absorption of carbon was the most significant in autumn (+0.40±0.41 W m−2). Uncertainty of these data was obtained by using the theory of error propagation and by taking into consideration the standard deviation of the experimental parameters. The relatively high values of the calculated relative standard deviations of the climate forcing data were attributed partly to the large number of the model parameters (9 and 11) and partly to their large uncertainty. The calculated uncertainties of various forcings were found to be in between the factors of 1.7 and 2.1 which were lower than those generally applied in forcing calculations. Parameter sensitivity analysis of the model equation proved that the reliability of the calculated data could be improved if attention is paid to the measurement of certain parameters such as: mass concentration, cloud coverage, surface albedo, upscattered fraction, single-scattering albedo and the fractional transmittance of the atmosphere.
Keywords: Regional radiative forcing; Ammonium sulfate; Total carbon; Error propagation; Parameter sensitivity;

Measurements of ammonia emissions from oak and pine forests and development of a non-industrial ammonia emissions inventory in texas by Golam Sarwar; Richard L. Corsi; Kerry A. Kinney; Joel A. Banks; Vince M. Torres; Chuck Schmidt (7137-7153).
Estimates of non-industrial source ammonia emissions in Texas were developed through the use of published emission factors and activity data for those sources. A total of 64 non-industrial source emission sub-categories were addressed, each falling into one of seven major source categories: animal husbandry, fertilizer applications, on-road vehicles, non-road sources, municipal wastewater disposal, domestic sources, and natural soil and vegetation. Annual statewide ammonia emissions were initially estimated to be 921,000 metric tons, with greater than 50% originating from natural soil and vegetation. However, estimates for pine and oak forests were characterized as having a great deal of uncertainty. A series of field sampling events were conducted to determine ammonia fluxes from pine and oak forest floors in east Texas. Both dynamic and static chamber methods were used. The ammonia flux averaged 0.09 kg km−2  month−1 for pine forests and 0.13 kg km−2  month−1 for oak forests. These values are significantly lower than those previously measured and cited in the published literature. However, the ammonia fluxes measured in east Texas forests are reasonably consistent with those predicted using mechanistic models for evergreen pine and deciduous broadleaf forests in Alabama, California, Colorado, and Tennessee. Statewide annual ammonia emissions estimates, revised using the newly developed ammonia fluxes for oak and pine forests in Texas, dropped from 921,000 to 467,000 metric tons. The relative contribution of ammonia emissions from pine and oak forests dropped from 49% to less than 1%. Animal husbandry was predicted to be the dominant non-industrial source, accounting for approximately 77% of non-industrial source ammonia emissions.
Keywords: Ammonia emissions; Soil; Forests; Inventory;

During the winter of 2005, physicochemical properties of size-fractionated PM10 particles were analyzed next to State Route 110 (Pasadena freeway in Los Angeles, CA, USA), a light-duty vehicle freeway, closed to heavy-duty traffic. We report volatility of ultrafine particles and chemical characteristics in the coarse, accumulation, and ultrafine modes very close to the freeway and at an urban background site. For measurement of mass and chemical composition, the study employed in each location a Micro-Orifice Uniform Deposit Impactor (MOUDI) and a modified high-volume sampler. Both instruments sampled with the same size cutpoints. A tandem differential mobility analyzer (TDMA) was used at the two sampling sites to analyze the semivolatile fraction of the aerosols. Size distributions of the ambient aerosol were measured using a DMA and total number concentration using a condensation particle counter (CPC).In this study, which was a continuation of a campaign during summer 2004, we compared the seasonal, i.e. winter versus summer, and diurnal, i.e. daytime versus evening, variation in PM characteristics in the vicinity of this freeway. Conditions in winter differed most from those in summer during the evening rush-hour traffic, with much lower temperatures in the winter campaign. Diurnal variations in particle volatility were observed, with higher content of volatile material in aerosols sampled in the evenings. Particle number concentrations were also much higher during the evening hours, increasing from 67,000 to 110,000 cm−3. The average total number concentration next to the freeway was 80,000 cm−3 during the sampling period, which was higher than in summer, when the average was 46,000 cm−3. External mixing was observed with increasing nonvolatile fractions for 40, 80, and 120 nm particles (39% of particles). In general the volatility increased in the evenings, while the nonvolatile fraction decreased.
Keywords: Urban aerosols; Ultrafine particles; Freeways; Volatility; Chemical composition; Tandem differential mobility analyzer (TDMA);

It is widely known that the formation of ozone (O3) is chemically linked to the emissions of nitrogen oxides (NO x ) and volatile organic compounds (VOC). This chemical interdependence is highly complex and gives rise to non-linear and coupled pollutant formation processes. In the present study, airborne measurements of sulfur dioxide (SO2), total reactive oxides of nitrogen (NO y ), and O3 taken from an instrumented aircraft within MECAPIP-1989 project have been reexamined to asses the governing photochemical processes of ozone formation. This experiment was carried out in the Castellón urban-industrial area, located on the Mediterranean coast of the Iberian Peninsula. Noon near field (within a 25-km radius from the coast line) transects show a strong ozone titration effect downwind of the main source area. Moreover, while afternoon measurements still depict ozone consumption near the emissions area, ozone net formation is observed in the mid-field (within a 75-km radius) of the Castellón urban-industrial complex. Ozone yields have been derived from these aircraft measurements. This analysis shows that there is almost no O3 production for the noon period. Conversely, the O3 yield reaches a maximum downwind of the emissions complex for the afternoon hours. Furthermore, measured values for the O3/NO y ratio have been used as photochemical indicators to determine the effectiveness of VOC or NO x controls in decreasing O3 abundance. The concentrations of these indicator species have been calculated from a series of simulations using a lagrangian photochemical model and good agreement has been observed between modeled and measured data. The sensitivity of ozone to changes in its primary sources has been examined by simulating scenarios with varying rates of NO x and VOC emissions. The results presented here show that for this particular case the measured and modeled O3/NO y ratios seem to identify a photochemical regime in which reductions in upwind NOx sources are more effective for lowering O3 than are VOC emissions.
Keywords: Photochemical non-linearities; Photochemical modeling; Air quality; MECAPIP; Spain;

A technique is presented for coupling receptor to dispersion models using a genetic algorithm to optimize the calibration factors, linking the two models. The backward-looking receptor model is based on the chemical mass balance model, but in this case, is formulated to break down pollutant contributions according to independent meteorological periods. For demonstration purposes the dispersion model is a basic Gaussian plume model, but could easily be substituted with a more refined model. The key to linking these two models is a genetic algorithm.The technique described here could prove useful for apportioning monitored pollutant to its sources, calibrating dispersion models, source position identification, monitor siting, and estimating total uncertainty.
Keywords: Source apportionment; Receptor model; Dispersion model; Coupled model; Genetic algorithm;

Investigations have been conducted at the Center for Space Research (CSR) into approaches to correlate MODIS aerosol optical thickness (AOT) values with ground-based, PM2.5 observations made at continuous air monitoring station locations operated by the Texas Commission on Environmental Quality (TCEQ). These correlations are needed to more fully utilize real-time MODIS AOT analyses generated at CSR in operational air quality forecasts issued by TCEQ using a trajectory-based forecast model developed by NASA. Initial analyses of two data sets collected during 3 months in 2003 and all of 2004 showed linear correlations in the 0.4–0.5 range in the data collected over Texas. Stronger correlations (exceeding 0.9) were obtained by averaging these same data over longer timescales but this approach is considered unsuitable for use in issuing air quality forecasts. Peculiarities in the MODIS AOT analyses, referred to as hot spots, were recognized while attempting to improve these correlations. It is demonstrated that hot spots are possible when pixels that contain surface water are not detected and removed from the AOT retrieval algorithms. An approach to reduce the frequency of hot spots in AOT analyses over Texas is demonstrated by tuning thresholds used to detect inland water surfaces and remove pixels that contain them from the analysis. Finally, the potential impact of hot spots on MODIS AOT-PM2.5 correlations is examined through the analysis of a third data set that contained sufficient levels of aerosols to mask inland water surfaces from the AOT algorithms. In this case, significantly stronger correlations, that exceed the 0.9 value considered suitable for use in a real-time air quality prediction system, were observed between the MODIS AOT observations and ground-based PM2.5 measurements.
Keywords: Remote sensing; MODIS; Air quality prediction; Aerosol optical thickness;

Professor Frans Nieuwstadt by H. van Dop (7204-7205).