Atmospheric Environment (v.39, #4)

Issues in model validation: assessing the performance of a regional-scale acid deposition model using measured and modelled data by S.E. Metcalfe; J.D. Whyatt; J.P.G. Nicholson; R.G. Derwent; E. Heywood (587-598).
The development and validation of a new version of the Hull Acid Rain Model (HARM12.1) is described in the context of changes in emissions and deposition estimates supplied by the Centre for Ecology and Hydrology (CEH) Edinburgh based on the available measurement networks. Major changes to the model include greater vertical resolution, the adoption of new background concentrations and ecosystem-specific deposition velocities. HARM output for 1998–2000 is compared with data from the rural SO2, NO2 and NH3 networks and results from the nitric acid and aerosol network. The ability to reproduce deposition estimates based on measurements is key to a regional-scale model like HARM. Changes in these estimates between 1995–97 and 1998–2000 are discussed. Comparing HARM modelled deposition and the CEH data indicates that the new version of the model performs better in this respect than its predecessor (HARM11.5). The trend in deposition over the time period does not seem to reflect the marked reduction in emissions. The possible reasons for this are explored with particular emphasis on changes in precipitation. 1995–97 was unusually dry, while 1998–2000 was wet. Changes in rainfall concentration and unmodified deposition are presented for comparison with HARM and CEH estimates. It is clear that the impact of precipitation variability on modelled acid deposition requires further investigation. Finally, we compare HARM12.1 and HARM 11.5 deposition in 2010 following emissions reductions to meet the terms of the National Emissions Ceilings Directive.
Keywords: Hull Acid Rain Model (HARM); UK; Model development; Validation; Trends;

Unique daily measurements of water-soluble organics in fine (<2 μm) and coarse (>2 μm) aerosols were conducted at Alert in the Canadian Arctic in winter to spring of 1992. They yield insight into photochemical production and loss of organics during long-range transport and ozone depletion events following polar sunrise. Comprehensive analyses of α, ω-dicarboxylic acids (C2–C12), ω-oxocarboxylic acids (C2–C9) and α-dicarbonyls (C2, C3) as well as pyruvic acid and aromatic (phthalic) diacid were conducted using GC and GC/MS techniques. Oxalic (C2) acid was generally the dominant diacid species in both fine and coarse fractions, followed by malonic (C3) and succinic (C4) acids. Concentrations of total diacids in the fine aerosol fraction (0.2–64 ng m−3) were 5–60 times higher than those in the coarse fraction (0.01–3 ng m−3). After polar sunrise in early-March, the total concentration of fine aerosol diacids increased by a factor of 3–5 while the coarse mode did not change significantly. From dark winter to sunlit spring, temporal changes in correlations and ratios of these water-soluble organics to vanadium and sulfate measured simultaneously suggest that atmospheric diacids and related organic compounds are largely controlled by long-range atmospheric transport of polluted air during winter, but they are significantly affected by photochemical production. The latter can occur in sunlight either during transport to the Arctic or during photochemical events associated with surface ozone depletion and bromine chemistry near Alert in spring. Conversion of gaseous precursors to particulate matter via photochemical oxidation was intensified at polar sunrise, resulting in a peak in the ratio of total diacids to V. During ozone depletion events, complex patterns are indicated in photochemical production and loss depending on the diacid compound. Unsaturated (maleic and phthalic) diacids were inversely correlated with particulate Br whereas saturated diacids (C2–C4) positively correlated with particulate Br. These results suggest that Br chemistry associated with ozone depletion leads to degradation of unsaturated diacids and to the production of smaller saturated diacids.
Keywords: Dicarboxylic acids; Long-range transport; Photochemical production; Polar sunrise; Vanadium; Bromine;

Comparison of driving characteristics in cities of Pearl River Delta, China by Wing-Tat Hung; Ka-Man Tam; Chi-Pang Lee; Lo-Yin Chan; Chun-Shun Cheung (615-625).
The cities in Pearl River Delta (PRD), China are going to merge into a big economy in the coming years. Hong Kong, Macao and Zhuhai are the three leading cities in PRD. A Hong Kong–Zhuhai–Macao Bridge is being actively proposed to link up these three cities. It will result in the changes of driving characteristics and thus, vehicle emissions. To quantify the impacts of emissions, we adopted a three-step approach to analyze the driving characteristics in these three cities. The approach involved deriving 10 driving parameters; the speed acceleration probability matrices (SAPM) as well as the driving cycles which allowed easy visualization of the driving characteristics. Car chasing technique was employed to collect speed–time data in peak and non-peak periods on both weekdays and weekends. The experimental cars were equipped with infrared tachometer, Global Positioning System receiver and microwave speed sensor. Through comparisons, we found major differences in driving characteristics including magnitude as well as spread and time proportions of driving speeds. These differences were attributed by the road network layout, vehicle density and driving behaviour. Aggressive driving and low driving speeds in urban cities would generate higher vehicle emissions.
Keywords: Driving characteristics; Car chasing technique; Speed acceleration probability matrix; Driving cycle; Speed sensor;

Multi-day ozone formation for alkenes and carbonyls investigated with a master chemical mechanism under European conditions by R.G. Derwent; M.E. Jenkin; S.M. Saunders; M.J. Pilling; N.R. Passant (627-635).
A photochemical trajectory model together with a master chemical mechanism and a highly speciated emission inventory have been used to characterise the multi-day formation of photochemical ozone in north west Europe for 123 organic compounds. Multi-day reactivity is apparent for both short-lived as well as long-lived organic compounds and arises for a number of mechanistic reasons. Unreacted organic compounds may be carried over from one day to the next. Degradation products formed on the first day may take part in the formation of ozone over longer timescales compared with those of ozone formation from parent compounds. For the highly reactive alkenes and carbonyls, two additional mechanisms account for much of the ozone formation on the second day. These involved the formation of peroxyacylnitrates and aldehydes during the first day which were carried over into the second day to stimulate additional ozone formation. The implications of these findings are discussed for the highly simplified and parameterised chemical mechanisms employed in some policy applications.
Keywords: Ozone; Organic compounds; Reactivity; Alkenes; Carbonyls;

Chemical characterisation of PM2.5, PM10 and coarse particles at urban, near-city and rural sites in Switzerland by Christoph Hueglin; Robert Gehrig; Urs Baltensperger; Martin Gysel; Christian Monn; Heinz Vonmont (637-651).
Daily PM2.5 and PM10 samples were taken from April 1998 to March 1999 at urban kerbside, urban background, near-city, and rural sites in Switzerland. The samples were analysed for mass, water soluble ions, trace elements, as well as elemental and organic carbon. The present paper focuses on the variation of element concentration between different site types and on the chemical mass closure of atmospheric particulate matter.Information on emission sources of trace elements is obtained by evaluation of the element abundances at sites that represent different pollution levels. The abundances of Ba, Ca, Ce, Cu, Fe, La, Mo, Mn, Pb, Sb, and Rh are gradually decreasing from urban kerbside to urban background, near-city and rural sites, indicating that road traffic is a main source of these elements. On the other hand, the abundances of Al, As, Cd, K, and V are similar for the different site types, which implies that emission sources are either spatially uniformly distributed (e.g. mineral dust), or there are no important regional emission sources and the ambient concentration of these elements might be dominated by long-range transport.When performing a mass closure, the annual average of the sum of aerosol chemical components was 22–27% for PM10 and 8–15% for PM2.5 lower than the PM mass. A drying procedure applied to a subset of PM10 samples and model calculations for PM2.5 samples according to their inorganic composition were used to estimate the contribution of retained water to the unaccounted mass at 50% RH. The obtained average water content was 10.6% for PM10 and 13–23% for PM2.5, clearly indicating that water is a major contributor to the unaccounted mass. Furthermore, a pronounced seasonal variation was observed with relatively lower water content in the colder season, indicating that the inorganic salts were mainly crystalline in winter, whereas they were probably dissolved during the rest of the year.
Keywords: PM10; PM2.5; Trace elements; Water content; Mass closure;

In this study, three methods (bucket, plate for downward flux and upward flux, and water vessel) were used to measure atmospheric dry deposition fluxes at three different heights (0.5, 1.5 and 12.5 m) to estimate the deposition fluxes of mass and polycyclic aromatic hydrocarbons (PAHs) in TERC (Tsukuba), Japan. Ambient particles were also collected using a high-volume air sampler, and ambient particle size distributions between 0.01 and 13.1 μm were measured using a low-pressure cascade impactor to characterize the PAH levels and dry deposition. Settling velocities were calculated as the settling fluxes divided by the corresponding average ambient particle concentrations. In this research work, ‘we describe how small particles dominate atmospheric dry deposition of PAHs and how bucket deposition fluxes and net (downward minus upward) fluxes decrease with height due to resuspension and/or vertical distribution of suspended particles’ etc.
Keywords: Polycyclic aromatic hydrocarbons; Atmospheric deposition; Net flux; Settling velocity;

A flux frame method using recurved passive ammonia flux (PAF) samplers for the measurement of distributed outdoor agricultural sources of ammonia (NH3) was evaluated in a controlled environment. The collection efficiency of the samplers was determined in a wind tunnel at controlled values of NH3 flux density (0.77–13.5 mg NH3  m−2  s−1), and over a range of angles of orientation to the flow direction (0°, 30°, 60°, 70°, 80° and 90°). The samplers were effective up to a wind speed of 7 m s−1 and an angle of 80° with a mean collection efficiency of 71%. The flux frame method had a mean collection efficiency of 87.4% when used with ground level point sources under controlled conditions in an open-circuit wind tunnel with boundary layer airflow characteristics.
Keywords: Ammonia recovery efficiency; Passive flux sampler; ADMS; Point source; Wind speed; Concentration;

Recurved passive ammonia flux (PAF) samplers based on absorption by oxalic acid were evaluated in two contrasting field environments. First, a flux frame 12 m high and 55.2 m long was used to support a vertical array of up to 156 flux samplers downwind of a controlled point or line source of ammonia (NH3). The upwind distance of the NH3 source was chosen so that the whole NH3 plume was captured by the flux frame. These measurements were used to calibrate the flux frame's collection efficiency (CE). The plume dispersion was modelled with ADMS. Second, individual columns of seven flux samplers at heights between 0.3 and 10.4 m were used to measure the NH3 emissions from a free-range sow paddock. The controlled release measurements gave measured overall CEs of over 80% and strong agreement between the measured and modelled flux densities ( R 2 > 0.9 ). The farm measurements showed that this method is insufficiently sensitive for use in a climate for which the wind direction and other critical meteorological parameters may vary widely throughout the several days required for a measurement.
Keywords: Passive flux sampler; Free-range pig; ADMS; Point source; Line source;

Contrasting effects of ozone under different water supplies in two Mediterranean tree species by Àngela Ribas; Josep Peñuelas; Susana Elvira; Benjamín S. Gimeno (685-693).
The effects of ozone (O3) exposure under different water availabilities were studied in two Mediterranean tree species: Quercus ilex and Ceratonia siliqua. Plants were exposed to different O3 concentrations in open top chambers (charcoal-filtered air (CF), non-filtered air (NF)) and non-filtered air plus 40 ppbv of O3 ((7:00–17:00 solar time) (NF+)) during 2 years, and to different water regimes (IR, sample irrigation, and WS, reduced water dose to 50%) through the last of those 2 years. AOT40 in the NF+ treatment was 59265 ppbv  h (from March 1999 to August 1999) while in the NF treatment, the AOT40 was 6727 ppbv  h for the same period. AOT40 was always 0 in the CF treatment. WS plants presented lower stomatal conductances and net photosynthetic rates, and higher foliar N concentrations than IR plants in both species. The irrigation treatment did not change the response trends to ozone in Q. ilex, the most sensitive species to O3 ambient concentrations, but it changed those of C. siliqua, the least sensitive species, since its ozone-fumigated WS plants did not decrease their net photosynthetic rates nor their biomass accumulation as it happened to its ozone-fumigated IR plants. These results show interspecific variations in O3 sensitivity under different water availabilities.
Keywords: Biomass reduction; Ceratonia siliqua; Ozone exposure; Quercus ilex; Low water supply; Species-specific ozone response; Water–ozone interactions;

Hydrogen sulfide and carbonyl sulfide in the museum environment—Part 1 by Hubertus A. Ankersmit; Norman H. Tennent; Simon F. Watts (695-707).
This paper discusses H2S and OCS measurements in a variety of museums. It addresses several issues of interpretation of those results, such seasonal and spatial variation, effects of sources and sinks local to the measurement. Typical indoor H2S concentrations found vary from 86 to 600 ppt, whereas OCS varies from 400 to 850 ppt. A lowest observed adverse effect dose (LOAED) for H2S and silver is defined (3.85 μg m−3  yr−1 ∼2.5 ppb yr−1). All museum H2S concentration data collected by the authors thus far is compared to this LOAED and in the main found to be considerably lower. Therefore tarnishing is not solely a function of H2S, instead is the result of multiple factors.
Keywords: Hydrogen sulfide; Reduced sulfur compounds; Museum atmospheric environments;

One in twelve day sampling for ambient PM2.5 was conducted at two sites in Missoula, Montana, from March 2000 to March 2001. In conjunction with measured PM2.5 mass and chemical species collected from both an urban site two blocks from a major intersection and a rural site at the opposite end of Missoula Valley, fingerprints of significant sources of PM2.5 specific to Missoula Valley served as inputs into a chemical mass balance (CMB) receptor model (version 8.0) to apportion the sources of the fine fraction. Model results revealed that the largest source throughout the year at both the urban and rural background sites was wood combustion, contributing an average of 41% to the fine fraction. The identified wood combustion included residential wood combustion during the winter, slash and prescribed burns from the surrounding areas during the spring and fall, and smoke from wildfires during the summer of 2000. The second largest source of PM2.5 in Missoula Valley throughout the year was diesel exhaust (19%), followed by secondary ammonium nitrate (17%), a kraft recovery boiler (14%) and hog fuel boilers (6%) from local wood products industry, and street sand (5%). During the forest fire season of summer 2000, CMB results of samples collected during smoky conditions on 13 August 2000 and 25 August 2000 revealed that 81% of the ambient PM2.5 came from wood combustion (forest fires).
Keywords: Speciation; Fine fraction; Montana; Environmental chemistry; Valley air pollution;

Assessment of the visibility impact of a plume emitted by a desulphuration plant by L. Presotto; R. Bellasio; R. Bianconi (719-737).
Wet plumes become visible when vapour condenses. In such a situation visible plumes may create some concerns in the population. A method to reduce the occurrence and the size of visible plumes is to increase the stack emission temperature.The mathematical model presented by Janicke and Janicke (Atmos. Environ. 35 (5) (2001) 887), using a revised entrainment formulation, was implemented in a computer code to deal with sequential records of meteorological conditions.The predictions of this model have been compared with experimental data giving satisfactory results. Then the model has been used for simulating the occurrence and the size of visible plumes from a stack with a scrubber and for three different emission temperatures.
Keywords: Wet plumes; Visibility; Plume rise; Scrubber;

To investigate the nature of individual Asian dust storm particles, an intensive field measurement was carried out on the west coast of Japan during a dense Asian dust storm event in March 2002. The giant particles (>5 μm) marked 124 times higher number concentration in the Asian dust storm event than in a non-Asian dust storm period. For the quantification analysis of the ultratrace elements in the size-resolved individual particles, an X-ray microprobe system equipped with super photon ring-8 GeV (SPring-8) BL-39XU was employed. By using this SPring-8 system we could successfully carry out the reconstruction of elemental maps and the quantification analysis of multiple elements in individual particles. The mass of Si showing the maximum value in individual particles was varied in the range from 1.2×10−2  pg to 1.1×100  pg with median 1.4×10−1  pg. In the case of S, mass ranged from 1.6×10−2  pg to 6.7×10−2  pg with median 3.9×10−2  pg, while several minor trace elements like V, Cr, Cu, and Zn show relatively low masses. A strong particle-size dependency of elemental masses was found for all elements, in particular the elemental masses of soil-derived components showed the monomodal maximum values around 2.05–5.07 μm particle size. From the X-ray, fluorescence images replayed corresponding to individual particles, we could simply categorize the visualized particles into two groups, namely internally mixed particles and externally mixed particles. From the factor analysis with variables of each elemental mass in individual particles, 79% of total particle population was found to be modified by sea-salt and sulfur.
Keywords: Asian dust storm; Individual particles; X-ray microprobe system; Elemental mass; Modification;

Modeling study of reactive gaseous mercury in the urban air by Zang-Ho Shon; Ki-Hyun Kim; Min-Young Kim; Meehye Lee (749-761).
Chemical speciation and concentrations of reactive gaseous mercury (RGM) in the urban atmospheric boundary layer (ABL) have been modeled using a photochemical box model. Measurements for gaseous elemental mercury (GEM) and the relevant trace gases were carried out in Seoul (37.6°N, 127°E), Korea, during a one-year period from March 2001 to February 2002. A moderately strong inverse correlation between GEM (Hg(0)) and ozone was observed in the spring. In addition, it was also observed that there were distinct GEM concentration differences between day and night, especially in the winter. Model simulations suggested that the most dominant sink of elemental mercury (Hg(0)) was the reaction with O3, which in turn contributed significantly to the formation of mercury oxide (HgO). The dominant RGM species in the urban ABL are likely to be HgO and Hg(HO)2. Seasonally averaged concentrations of HgO and Hg(HO)2 are estimated to range from 0.5×104 to 1.1×104 and 0.2×104 to 3.5×104  molecules cm−3, respectively. According to our model simulations, most RGM species are expected to exhibit relatively enhanced concentrations during the daytime compared to the nighttime.
Keywords: Gaseous elemental mercury; Reactive gaseous mercury; Urban; Photochemical box model; Halogen;

A semi-empirical correlation for the rate coefficients for cross- and self-reactions of peroxy radicals in the gas-phase by Dudley E. Shallcross; M. Teresa Raventos-Duran; Max W. Bardwell; Asan Bacak; Zachary Solman; Carl J. Percival (763-771).
Peroxy radicals play an important role as reaction intermediates in the atmospheric oxidation of volatile organic compounds (VOCs). The rate coefficients for the self-reactions vary by up to six orders of magnitude (e.g. 3.0×10−17  cm3  molecule−1  s−1 for t-C4H9O2 and 1.5×10−11  cm3  molecule−1  s−1 for CH3C(O)O2) with, up to now, no clear pattern. This work represents the first rationalisation of peroxy radical self-reaction trends in reactivity. A correlation between the logarithm of the rate coefficient of peroxy radical self-reactions with the stabilisation energy, the difference in the enthalpy of formation of peroxy radicals with that of the tetraoxide adduct {ΔH f(RO4R)−2ΔH f(RO2)}, is presented. The equation, log10k=−{ΔH f(RO4R)−2ΔH f(RO2)+235.95}/13.32 (where energy is in kJ mol−1) is given to predict the room temperature rate coefficients of peroxy radical self-reactions. The correlation was extended to predict rate coefficients for the cross-reactions of peroxy radicals with CH3O2. Furthermore, favourable comparisons are made between the predicted rate coefficients and very recent studies of complex peroxy radical systems.
Keywords: Peroxy radicals; Self-reaction; Cross-reaction; Kinetics; Correlations;

Boundary-layer evolution over Phoenix, Arizona and the premature mixing of pollutants in the early morning by William J. Shaw; J. Christopher Doran; Richard L. Coulter (773-786).
The 2001 Phoenix Sunrise campaign was a field measurement program to investigate the early morning chemical and meteorological processes associated with the development of ozone pollution in Phoenix, Arizona. As part of that study, atmospheric structure was measured using wind profiling radars, sodars, and radiosondes at several locations in the Phoenix metropolitan area. Chemical measurements made by other investigators showed that vertical mixing of pollutants began prior to sunrise on a number of occasions. This was surprising, since we expected sustained mixing to occur only after sunrise and the onset of solar heating. We have used the meteorological measurements to identify a density current that commonly arrives in downtown Phoenix in the hour or two before sunrise when conditions are undisturbed. Both winds and cold advection associated with this feature act to destabilize the lower atmosphere, and the resulting mixing continues through the morning transition to convective conditions. Because photochemical production of ozone is non-linearly dependent on the concentrations of precursor species, this early mixing will need to be properly represented in combined meteorological and chemical models if they are to be fully successful in simulating ozone concentrations.
Keywords: Boundary layer; Complex terrain; Density current; Ozone; Air pollution;

The effect of compaction and covering during storage of beef cattle (Bos taurus) farmyard manure (FYM) on ammonia (NH3), nitrous oxide (N2O) and methane (CH4) emissions was determined. Gaseous emission measurements were made over three separate storage periods of between 90 and 109 days. The effect of the different storage treatments on manure chemical composition was also determined. Compaction was carried out as the manure was put into store and the compacted manures covered with plastic sheeting. Compaction and covering significantly reduced NH3 emissions from manure by over 90% during the first summer storage period ( P < 0.05 ) . Over the subsequent storage periods NH3 emissions from the FYM were small and unaffected by storage treatment. However, during the second storage period heavy and persistent rainfall during heap establishment and the following week appeared to reduce NH3 emissions markedly. The low ammonium-N content of the FYM in the third storage period may have reduced the risk of NH3 emission and reduced the relative effect of the compaction/covering treatment. Compaction and covering also significantly reduced N2O emissions from cattle FYM ( P < 0.05 ) by ca. 30% during the first storage period. Subsequent N2O emissions were unaffected by treatment. Methane emissions from cattle FYM were unaffected by treatment over the first storage period and were decreased by compaction in the second storage period yet was increased by compaction during the third storage period. It would appear that compacting and covering manure heaps does have the potential to reduce emissions of both NH3 and N2O when the manure contains relatively high ammonium-N contents. Additional benefits are that N and K are retained in the manure heap for agronomic benefit.
Keywords: Cattle FYM; Compaction; Covers; Ammonia; Nitrous oxide; Methane;