Atmospheric Environment (v.38, #9)

Ambient ammonia and ammonium aerosol across a region of variable ammonia emission density by J.T. Walker; Dave R Whitall; Wayne Robarge; Hans W. Paerl (1235-1246).
We present 1 year of ambient ammonia (NH3), ammonium (NH4 +), hydrochloric acid (HCl), chloride (Cl), nitric acid (HNO3), nitrate (NO3 ), nitrous acid (HONO), sulfur dioxide (SO2), and sulfate (SO4 2−) concentrations at three sites in the Coastal Plain region of North Carolina. The three sites, Clinton, Kinston, and Morehead City, are located in counties with total NH3 emission densities of 4800, 2280, and 320 kg NH3-N km−2  yr−1, respectively. Average NH3 concentrations were 5.32, 2.46, and 0.58 μg m−3 at Clinton, Kinston, and Morehead City, respectively. Average NH4 + concentrations were 1.84, 1.25, and 0.91 μg m−3, and total concentrations of inorganic (NH4 ++NO3 + SO4 2−+Cl) particulate matter with aerosol diameters <2.5 μm (PM2.5) were 8.66, 6.35, and 5.31 μg m−3 at Clinton, Kinston, and Morehead City, respectively. NH3 concentrations were highest during the summer at all sites, with summer-to-winter concentration ratios of 2.40, 5.70, and 1.70 at Clinton, Kinston, and Morehead City, respectively. NH3 concentrations were higher at night at the Clinton site, during the day at the Kinston site, and day vs. night concentrations were similar at the Morehead City site. NH4 + concentrations were highest during the winter at all sites, though this may not be representative of all years. Average daytime concentrations of NH4 + were similar to night values at all sites. NH4 + aerosol was primarily associated with SO4 2− at all sites, though the degree of SO4 2− neutralization was highest at Clinton and lowest at Morehead City. NH4 + aerosol formation appeared to be acid-gas-limited at the Clinton site during all seasons and during the spring and summer at the Kinston site. This study shows that agricultural NH3 emissions influence local ambient concentrations of NH3 and PM2.5.
Keywords: Atmospheric nitrogen; Agricultural emissions; Acid gases; PM2.5; Denuders;

Atmospheric distribution of organic compounds from urban areas near a coal-fired power station by Celeste Yara Moreira dos Santos; Débora de Almeida Azevedo; Francisco Radler de Aquino Neto (1247-1257).
Atmospheric particulate matter and volatile organic compounds (VOCs) from three sites surrounding a thermoelectric complex, VOCs from the power plant stack gas and aliphatic and aromatic fractions obtained from a coal sample utilized by the thermoelectric complex were monitored in Tubarão and Capivari de Baixo cities, State of Santa Catarina, Brazil, in December 1997. Literature data were reviewed in order to outline differences and similarities among sources and levels of pollutants from coal combustion. Concentrations of benzo[a]pyrene, which is a well-known carcinogenic chemical, were relatively high compared to large urban agglomerations worldwide and similar compared to Asian cities as Beijing in China, a substantial producer and consumer of coal. Concentrations of benzene were lower than other Brazilian urban areas. Quantitation of the compounds identified showed that they were present within the recommended limits of exposure for substances present in air.
Keywords: Power plant; Benzo[a]pyrene; Benzene,VOCs; Levoglucosan; PAH,Coal;

Convective transport of reactive constituents to the tropical and mid-latitude tropopause region: I. Observations by B. Ridley; E. Atlas; H. Selkirk; L. Pfister; D. Montzka; J. Walega; S. Donnelly; V. Stroud; E. Richard; K. Kelly; A. Tuck; T. Thompson; J. Reeves; D. Baumgardner; W.T. Rawlins; M. Mahoney; R. Herman; R. Friedl; F. Moore; E. Ray; J. Elkins (1259-1274).
Measurements of ozone, reactive carbon and nitrogen, and other trace constituents from flights of the NASA WB-57F aircraft in the upper troposphere and lower stratosphere reveal that convection in the tropics can present a complex mix of surface-emitted constituents right up to the altitude of the lapse rate tropopause. At higher latitudes over the southern US, the strongest transport signal, in terms of constituent mixing ratios, occurred in the potential temperature range of 340–350 K or approximately over the altitude range of 9–11 km. Weaker convective signals were also seen up to near the tropopause. There was no evidence of convective transport directly into the lower stratosphere from these flights.
Keywords: Convection; Aircraft measurements; Tropical tropopause; Nitrogen oxides; Hydrocarbons; Methyl iodide; Methyl nitrate; Upper troposphere; Lower stratosphere; Chemical tracers;

Daily particulate matter samples were collected during 1 year from 7 November 1997 to 31 October 1998 in Beijing area, at two monitoring sites, the Ming Tomb (a background site) situated northernmost of the basin and the Temple of Heaven (a residential site) inside the city. For 110 atmospheric aerosol samples organic carbon (OC) was determined with a two-step thermal procedure using a CHN elemental analyzer, and water-soluble potassium (K+) with flame atomic absorption spectrometry. The annual average of OC and K+ concentrations of the Ming Tomb site were 22.0 μg C m−3 and 1.21 μg m−3, respectively, while that of the Temple Heaven site were 41.5 μg C m−3 and 1.94 μg m−3. At the Ming Tomb site the monthly average of K+ concentration appeared the highest in June (3.07 μg m−3), three times as much as that in May (1.02 μg m−3). At the Temple Heaven site, the highest value was also in June (4.22 μg m−3 while 1.97 μg m−3 in May). Regression analysis results showed that at both sites the OC/K+ concentration ratio value (5) is what expected for biomass burning. Our results thus suggest that biomass burning influence is on a regional scale. It was calculated as an upper estimate, that at Ming Tomb site about 50%, 70%, and 46% of the OC concentrations in May, June, and July, respectively, were attributed to biomass burning while at the more urban site of Temple of Heaven, the biomass burning OC contribution is still high (32%, 43%, and 10% respectively). In the case of a severe pollution event in June 2000 in Beijing, it has been shown that temperature inversion and wind direction aggravated substantially air pollution caused by biomass burning. Our work suggests that biomass burning in the Beijing region is a significant repetitive pollution factor that cannot be neglected.
Keywords: Biomass burning; Organic carbon; Water-soluble potassium; Source identification;

The trends of the few-second-aged small positive air ion spectra caused by enhanced concentrations of certain trace gases (HCl, ammonia, HNO3, certain pyridine derivatives, (CH3)2SO, (C4H9)3N, C6H5CHO, CH3CN) have been studied. The measurements have been accompanied by the simulations of the chemical composition of the ions. Experiments, simulations, and chemical considerations confirmed that nitrogen containing organic molecules such as pyridine, picolines, lutidines are the relevant compounds of the ions. However, as discussed, the origin of the pyridinated compounds within the natural ions remains problematic, in certain cases the observed abundance of natural pyridine compound ions can be overestimated. Therefore, H3O+(H2O) n and NH4 +·X·Y cycles are specially discussed, and certain problematic ions can belong to these groups.
Keywords: Air pollution; Mobility spectra; Chemical composition; Few-second-aged small air ions;

During a 6 years period, the atmospheric activity concentrations of the long-lived 222Rn daughters and 7Be concentrations were measured at Málaga (36° 43′40″ N; 4° 28′8″ W). The concentration data of long-lived radon daughters and 7Be together with meteorological variables were used for a comprehensive regression analysis of weekly variation of radioactivity in air. The seasonal variations of the concentrations show similar trend for the long-lived daughters of radon and 7Be concentrations. The activity concentrations were observed to be higher during the summer months than in other seasons. From the ratio between the activity concentrations of 210Po and 210Pb, a mean residence time of aerosol particles in the atmosphere of about 31 days was obtained. The average concentrations values of 210Pb and 7Be over the 6 years period have been found to be 510 and 4.6 mBq m−3, respectively. A mean aerosol mass concentrations of (46.6±7.8) μg m−3 was also determined during the period of measurements. The 7Be/210Pb activity ratios varied between 11 and 8.4. Correlation study has been carried out between the aerosol mass and concentrations of these tracers.
Keywords: Radon decay products; 7Be; Surface air; Aerosols; Residence time; East mediterranean;

The major deficiency in linking the effects of environmental exposure to children's health is the lack of data on the exposure of children to hazardous environmental pollutants. Accordingly, the present study compared the personal volatile organic compound (VOC) exposure of children from four elementary schools at different proximities to the Daegu Dyeing Industrial Complex (DDIC) and adjacent to different traffic densities. The personal air concentrations of four VOCs (toluene, m,p-xylenes, and o-xylene) were significantly higher for the children attending the school (S1) closest to the boundary of the DDIC compared to the children attending the school (S2) further away. The DDIC was the likely primary cause for the elevated personal air concentrations of the four VOCs in the children attending the school nearest the DDIC. The personal exposure to toluene and methyl tertiary-butyl ether (MTBE) for the children attending the school near a major roadway with a high traffic density was significantly higher than that for the children attending the school near a roadway with a low traffic density. The difference in the breath concentrations was generally similar to the difference in the personal air concentrations among the children from the four schools. In contrast to the children attending schools in low-income areas, the children attending schools in high-income areas exhibited no significant difference in the concentrations of any of the target VOCs in the personal air and breath samples between the children living with and without a smoker in the home.
Keywords: Breath concentration; Children's exposure; Dyeing industrial complex; Elementary school; Personal air;

Spectral daily aerosol optical depths (τaλ ) estimated from a multi-filter radiometer over Kwangju were analyzed from January 1999 to August 2001 (total of 277 days). Optical depths obtained showed a pronounced temporal trend, with maximum dust loading observed during spring time and biomass burning aerosol in early summer and autumn of each year. Result indicates that τa501 nm increased from spring average of 0.45±0.02 to values >0.7 on 7 April 2000, and 13 April 2001. Daily mean spectral variations in the Ångström exponents α were also computed for various episode periods under consideration. A dramatic change in α value is noted especially at high aerosol optical depth when coarse mode aerosol dominates over the influence of accumulation-mode aerosol. High values of τaλ associated with high values of α in early June and October are characteristics of smoke aerosol predominantly from biomass burning aerosol. Also, volume size distribution is investigated for different pollution episodes with result indicating that the peak in the distribution of the coarse mode volume radius and fine mode particles of dust and biomass-burning aerosol respectively increases as aerosol optical depth increases at Kwangju. Air-mass trajectory were developed on 7–8 April and 19–20 October, 2000 to explain the transport of Asian dust particle and biomass burning to Kwangju.
Keywords: Yellow sand; Visibility; Aerosol optical depths; Trajectory; Volume size distribution;

Eurasian continental background and regionally polluted levels of ozone and CO observed in northeast Asia by Pakpong Pochanart; Shungo Kato; Takao Katsuno; Hajime Akimoto (1325-1336).
The roles of Eurasian/Siberian continental air masses transport and the impact of large-scale East Asian anthropogenic emissions on tropospheric ozone and carbon monoxide levels in northeast Asia were investigated. Seasonal behaviors of O3 and CO mixing ratios in background continental (BC) air masses and regionally polluted continental (RPC) air masses were identified using trajectory analyses of Eurasian continental air masses and multi-year O3 and CO data observed at Happo, a mountain site in Japan. RPC air masses show significantly higher O3 and CO mixing ratios (annual average of 53.9±6.0 and 200±41 ppb, respectively) than BC air masses (44.4±3.6 and 167±17 ppb, respectively). Large scale anthropogenic emissions in East Asia are suggested to contribute about 10 ppb of photochemical O3 and 32 ppb of CO at Happo. A comparative study of O3 and CO observed at other sites, i.e., Oki Islands and Mondy in northeast Asia, showed similarities suggesting that O3 mixing ratios in BC air masses at Happo could be representative for remote northeast Asia. However, CO mixing ratios in BC air masses at Happo are higher than the background level in Siberia. The overestimate is probably related to an increase in the CO baseline gradient between Siberia and the East Asia Pacific rim, and perturbations by sub-grid scale pollution transport and regional-scale boreal forest fires in Siberia when the background continental air masses are transported to Japan.
Keywords: Atmospheric pollution; Continental outflow; Long-range transport; Regional source; Trajectory analysis;

On estimating emissions through horizontal fluxes by Akula Venkatram (1337-1344).
This paper examines a popular method of estimating emissions from fugitive sources, which consists of computing horizontal fluxes using measured vertical profiles of velocities and concentrations at several locations downwind of a source. The horizontal flux is the height integral of the product of the velocity normal to the source and the concentration. If the losses between the source and the measurement location are small, the emission rate per unit length of the source is the horizontal flux. The calculation of horizontal flux is not straightforward because we need to make assumptions about the behavior of the concentration profile; the concentration measurements only suggest a plausible profile. We show that this uncertainty in the calculation can be reduced by using a dispersion model to interpret the data. We then provide a quantitative basis for the discussion by comparing horizontal flux calculations presented by Veranth et al. (Atmospheric Environment 37 (2003) 2295) with emissions inferred from a dispersion model applied to the same data set.
Keywords: Fugitive emissions; Dispersion model; Surface layer dispersion; Horizontal fluxes; Unpaved roads; Emission factors; Particle deposition;

Primary and secondary carbonaceous species in the atmosphere of Western Riverside County, California by Kwangsam Na; Aniket A. Sawant; Chen Song; David R. Cocker (1345-1355).
Elemental carbon (EC), organic carbon (OC) and PM2.5 mass concentrations were measured from September 2001 through January 2002 in Mira Loma, CA. EC and OC were analyzed using the NIOSH (National Institute of Occupational Safety and Health) 5040 thermal/optical transmittance method. OC concentrations in Mira Loma were found to be higher than those of other urban sites in the South Coast Air Basin (SoCAB), while EC concentrations were comparable to or lower than those of other SoCAB sites. Overall, OC and EC concentrations accounted for 26% and 5% of the total PM2.5, respectively. OC/EC ratios ranged from 1.6 to 12.8 with an average of 5.2. These values were higher than those observed at other urban sites in the United States by a factor of 2. A stronger correlation between suspended OC and EC concentrations was noted in months with lower photochemical activity (December and January, r=0.82) than in months with greater photochemical activity (September and October, r=0.64). The elevated levels of OC, OC/EC ratios, and the seasonal difference in correlation between OC and EC concentrations were attributed in part to significant secondary organic aerosol formation. The fraction of total organic carbon that was secondary organic carbon (SOC) was estimated using the OC/EC minimum ratio method and Chemical Mass Balance (CMB) modeling. Based on the OC/EC minimum ratio method, the contribution of SOC to the total organic carbon tended to be higher during the months with greater photochemical activity (63%) than those with lower photochemical activity (44%). Based on CMB modeling, SOC contributed to 14% of the total PM2.5 mass and 57% of the total organic carbon during the study period. Overall, these findings suggest that photochemical activity can appreciably affect total PM2.5 mass concentrations in Mira Loma, and that measures to control emissions of SOC precursors incorporated as part of a region-wide air quality management plan could lead to a perceptible drop in total PM2.5 mass concentrations in this area.
Keywords: Organic carbon; Elemental carbon; PM2.5; OC-to-EC ratio; Secondary organic carbon;

A process-based model of ammonia emissions from dairy cows: improved temporal and spatial resolution by Robert W. Pinder; Natalie J. Pekney; Cliff I. Davidson; Peter J. Adams (1357-1365).
This research has developed an integrated model of a dairy farm that predicts monthly ammonia emission factors based on farming practices and climate conditions, including temperature, wind speed, and precipitation. The model can be used to predict the seasonal and geographic variations in ammonia emission factors, which are important for accurately predicting aerosol nitrate concentrations. The model tracks the volume of manure and mass of ammoniacal nitrogen as the manure moves through the housing, storage, application, and grazing stages of a dairy farm. Most of the processes of ammonia volatilization are modeled explicitly, but poorly understood processes are parameterized and tuned to match empirical data. The tuned model has been compared to independent experimental data and is shown to be robust over the range of experimental conditions. We have characterized the differences in emissions resulting from changes in climate conditions and farming practices and found that both of these factors are significant and should be included when developing a national inventory.
Keywords: Ammonia; Emission inventory; Agriculture; PM 2.5; Aerosol;

Oxidation of organic films relevant to atmospheric aerosols by T.L. Eliason; J.B. Gilman; V. Vaida (1367-1378).
Recent field measurements have shown that a significant fraction of the mass of atmospheric aerosols is organic. Organic compounds will preferentially partition to the surface of the aerosols and are extremely susceptible to oxidation by •OH, O3, halogens, and NO3. In this work, organic films were investigated as proxies for surface alkane and alkene organic compounds. We have studied the chemical mechanisms for processing of an alkane and an alkene by •OH. The competition between O3 and •OH for the carbon–carbon double bond in an alkene is also investigated. Atmospheric consequences of the oxidation of hydrocarbon films will be discussed, including the affects on atmospheric chemistry, climate and atmospheric transport.
Keywords: Reaction mechanism; Organic aerosol; Surface film; Atmospheric chemistry; Atmospheric oxidants;

Significant emissions of NO x (oxides of nitrogen: NO and NO2) are common from sources such as power stations, road tunnel ventilation outputs and freeways. As these species are chemically reactive (NO+O3→O2+NO2), their concentrations downwind from the source are influenced by both the atmospheric turbulence (dispersion) and the chemical reactions. As part of an ongoing research project to investigate the effects of mixing on chemical reactions in the atmosphere, we make use of a new modelling technique based on the concentration statistics of a non-reactive (conserved) scalar. A simplified form of the model is an upper (conservative) limit on toxic NO2 concentrations. The novelty of this limit is that it is less conservative than previous methods commonly in use by air quality modellers but has a sound physical basis and can readily be calculated for atmospheric plumes. Model results are presented for NO, O3 and NO2. When model predictions for NO2 are compared to atmospheric field data it is found that the model limit is a conservative bound on their concentrations. The present model is restricted to the plume centreline. The two main inputs are a parameterisation for the concentration fluctuations (conditional dissipation of scalar concentration fluctuations) and the probability density function (pdf) of the conserved scalar in the plume. Careful choices of these inputs are necessary for correct model behaviour and to ensure internal model consistency. Future work needed to improve present model limitations is described including: use of the pdf transport equation; ways to remove the need for model parameters by appeal to basic physics, and generalisation of the present centreline restriction.
Keywords: Turbulence; Dispersion; Chemical reaction; Smog; Conditional moment closure; Reaction dominated limit;