Atmospheric Environment (v.37, #28)

Mixture state of individual Asian dust particles at a coastal site of Qingdao, China by Daizhou Zhang; Jiaye Zang; Guangyu Shi; Yasunobu Iwasaka; Atsushi Matsuki; Dmitri Trochkine (3895-3901).
In order to investigate the characteristics of Asian dust particles before they leave the continent, particles were collected at a coastal site of Qingdao (120°27′E, 36°06′N) in northeastern China during three dust storm events in spring 2001. The elemental composition and size of individual dust particles, and their mixture state with sea salt, sulfate and nitrate were analyzed using electron microscopes and an energy dispersive spectrometer. It was found that far less than 10% of dust particles were internally mixed with sea salt. Although a number of dust particles contained Na, S, and Cl, the elements in most of the particles were more likely from crustal origins. The combination of reagent tests and elemental analysis revealed that 3.3–12.2% of dust particles contained sulfate and 6.5–10.0% contained nitrate on their surface. Number-size distributions of dust particles estimated from their electron microscope images had a distribution mode of around 3 μm diameter with the range of 1.0–8.0 μm. Out of this range, dust particles were rarely detected.
Keywords: Asian dust; Size distribution; Sulfate; Nitrate; Coastal area; Electron microscopy;

A receptor-oriented modelling system, consisting of a mesoscale meteorological model (RAMS) and a Lagrangian particle dispersion model (LPD) is applied to the determination of emissions of methane from livestock in agricultural regions in New Zealand. Aircraft measurements of methane mixing ratio profiles are input to the model, from which influence functions are obtained; these are the footprints of potential contributing emissions. Inversion techniques and statistical analysis enable the determination of confidence intervals for methane emissions. Results are compared with prior emissions data obtained by other methods.For two case studies in the Manawatu region of New Zealand in June 1995 and April 1997, methane emission fluxes of 54±32 and 56±54 mg m−2  d−1 are obtained (95% confidence intervals). These are consistent with independently estimated per-animal emission rates and observed livestock densities. For a field campaign in New Zealand's Waikato region in 1999, where no emissions estimates were available a priori, the average emission fluxes derived using receptor-oriented techniques are 67±46 mg m−2  d−1.The error-bars on the emission fluxes are arguably quite large. This is due to uncertainties in the methane observations and errors in the meteorological simulations, which play a different role in each case study. Improvements in both the experimental and modelling procedures are proposed to reduce uncertainties in the calculated emission fluxes.
Keywords: Greenhouse gas emissions; Pastoral agriculture; Mesoscale meteorology; Particle dispersion model; Confidence interval; Bayesian inversion techniques;

In this work attempts were made to elucidate the monoterpenic alcohol inhibition of the S(IV) autoxidation by comparing the inhibiting activity of cis-verbenol (C10H15OH), myrtenol (C10H15OH) and nopol (C11H17OH) with that of ethanol (C2H5OH) and 2-propanol (C3H7OH). Results of laboratory experiments on the kinetics of S(IV) autoxidation in the presence of these alcohols were interpreted using the equation derived by Alyea and Bäckström (J. Am. Chem. Soc. 51 (1929) 90), brought into relationship with the actual mechanistic knowledge on the reactivity of the inhibitors with respect to sulphate radicals. The rate constants for the reaction: alc+SO4 ·(+O2)→SO4 2−+H++HO2+ald involving cis-verbenol and myrtenol have been determined as equal to, respectively, 5.4×109 and 4.2×109   M −1   s −1 . These results were obtained under the assumption that the main chain termination is due to simultaneous scavenging SO5 · radical anions by FeII and SO4 · radical anions by an alcohol. In the case of nopol the rough estimate gave for the rate constant of the latter reaction a value of 9.0×109   M −1   s −1 burdened with an error caused by the sulphoxy radical induced autoxidation of nopol. The studied airborne compounds of biological origin were shown to be potentially significant modifiers of the acidity formation in clouds and a sink for sulphoxy radicals participating in further transformations of these compounds.
Keywords: Aliphatic alcohols; S(IV) autoxidation; Sulphur dioxide; Sulphoxy radicals; Terpenes;

Meteorological normalisation of time series of air quality data aims to extract anthropogenic signals by removing natural fluctuations in the collected data. We showed that the currently used procedures to select normalisation models can cause over-fitting to observed data and undesirable smoothing of anthropogenic signals. A simulation study revealed that the risk of such effects is particularly large when: (i) the observed data are serially correlated, (ii) the normalisation model is selected by leave-one-out cross-validation, and (iii) complex models, such as artificial neural networks, are fitted to data. When the size of the test sets used in the cross-validation was increased, and only moderately complex linear models were fitted to data, the over-fitting was less pronounced. An empirical study of the predictive ability of different normalisation models for tropospheric ozone in Finland confirmed the importance of using appropriate model selection strategies. Moderately complex regional models involving contemporaneous meteorological data from a network of stations were found to be superior to single-site models as well as more complex regional models involving both contemporaneous and time-lagged meteorological data from a network of stations.
Keywords: Meteorological normalisation; Model selection; Partial least-squares regression; Artificial neural networks; Cross-validation; Tropospheric ozone;

Gas-phase ozonolysis of α-pinene: gaseous products and particle formation by T. Berndt; O. Böge; F. Stratmann (3933-3945).
The gas-phase ozonolysis of α-pinene has been studied in a stopped-flow system at 295±2  K and 950  mbar of synthetic air as well as under flow conditions at 295±0.5  K and 1000  mbar of synthetic air. Gaseous products were analyzed using on-line GC-MS/FID and FT-IR measurements. The formation of new particles (dp⩾3  nm) was followed by means of a differential mobility particle sizer system and an ultra-fine condensation particle counter.First, the reaction of OH radicals with c-hexane was reinvestigated. Products were c-hexanol with a yield of 0.35±0.06 and c-hexanone with a yield of 0.53±0.06. The rate coefficients of the consecutive reaction of OH radicals with c-hexanol and c-hexanone of (2.7±0.4)×10−11 and (6.1±0.9)×10−12   cm 3   molecule −1   s −1 , respectively, were obtained. From the reaction of OH radicals with c-hexanol, a c-hexanone yield of 0.58±0.07 was observed. Using the c-hexane scavenger technique, an OH radical yield of 0.68±0.10 was measured for the reaction of O3 with α-pinene applicable for H2O concentrations of ∼1.5×1015 and 2.6×1017   molecule cm −3 .The formation yield of pinonaldehyde was found to be strongly dependent on the experimental conditions. Generally, the pinonaldehyde yield decreased for increasing α-pinene conversion. In the presence of an OH radical scavenger, maximum pinonaldehyde yields were 0.42±0.05 and 0.32±0.04 for [H2O]∼1.5×1015 and 2.6×1017   molecule cm −3 , respectively. Under the present conditions the pinonaldehyde formation cannot be described via the reaction of a Criegee intermediate with H2O. This finding is corroborated by measurements of the co-product H2O2. The formation yield of α-pinene oxide of 0.03±0.015 was unaffected by experimental conditions.Newly formed particles were measured for a relatively wide range of experimental conditions. Particle formation was only detectable for an α-pinene conversion above 3×1011   molecule cm −3 . The results of the present study suggest that the formation of new particles from the pure O3+α-pinene reaction is unlikely under atmospheric conditions.
Keywords: α-pinene; Ozonolysis; OH radicals; Particle formation;

Polar organic oxygenates in PM2.5 at a southeastern site in the United States by E.O Edney; T.E Kleindienst; T.S Conver; C.D McIver; E.W Corse; W.S Weathers (3947-3965).
A field study was undertaken in Research Triangle Park, NC, USA during the summer of 2000 to identify classes of polar oxygenates in PM2.5 containing carbonyl and/or hydroxyl functional groups and, to the extent possible, determine the individual particle-bound oxygenates that make up each class. The selected site was in a semi-rural environment with expected impacts from both biogenic and anthropogenic sources. PM2.5 samples were collected and analyzed for gravimetric mass, inorganic composition by ion chromatography, polar oxygenated compounds by gas chromatography-mass spectroscopy after derivatization of the solvent extracts, organic and elemental carbon (EC) by a thermal–optical method, and chemical functional groups by infrared (IR) spectroscopy. The chemical analyses also included determining the polarity of the PM2.5 by measuring the organic carbon (OC) concentrations in a series of extraction solvents of increasing polarity. The ambient PM2.5 mass concentrations ranged between 9 and 30 μg m−3, with an average mass composition of 28% sulfate, 6% nitrate, 12% ammonium, 39% OC compound, 2% EC, and 12% liquid water at a relative humidity of 43%. OC analyses of the organic extracts indicated approximately 89% of the extractable OC was more polar in nature than that extracted by n-hexane. IR analysis of the PM2.5 was consistent with the presence of significant levels of polar carbonyl and hydroxyl functional groups. The polar nature of the organic fraction was further supported by the observation that the inorganic fraction accounted for only about 80% of measured liquid water concentrations in the PM2.5. The mass spectra data were consistent with the presence of the following classes of oxygenates: oxo monocarboxylic acids, trihydroxy monocarboxylic acids, dihydroxy dicarboxylic acids, hydroxy dicarboxylic acids, normal dicarboxylic acids, oxo dicarboxylic acids, methoxy dicarboxylic acids, tricarboxylic acids, triols, and photooxidation products of α-pinene and toluene. In particular, five secondary organic aerosol compounds observed in a smog chamber irradiation of an α-pinene/NO x /air mixture were detected in ambient PM2.5.
Keywords: Polar organic compounds; PM2.5; Secondary organic aerosol; Substituted dicarboxylic acids;

Long-range transport for dry acidic deposition over South Korea has been estimated using a simplified chemical model and the K-mean clustering technique. The three consecutive daily mean National Center for Environmental Protection reanalyzed 850  hPa geopotential height fields without precipitation on the last day over South Korea are used for clustering of synoptic patterns for the period of 1994–1998. Two emission conditions are simulated for each cluster to estimate long-term impact by long-range transport for acidic dry deposition over South Korea. One condition takes all emissions within the simulated domain into account as a base case and the other condition excludes South Korea's emission and all oxidizers and considering all of the other emissions as a control case. The results of the present study indicate that the contribution of long-range transport to the annual total South Korea's dry deposition of sulfur is found to be about 30% (78  eq ha −1   yr −1), of which 65% and 35% are contributed by SO2 and SO4 2−, respectively, whereas that of total nitrogen deposition is found to be 49% (240  eq ha −1   yr −1), of which 80% and 20% are contributed by the transformed nitrogen species including HNO3, NH4 + and NO3 , and the primary pollutants of NO x and NH3, respectively, suggesting the importance of secondary pollutants of nitrogen species for long-range transport to South Korea's total dry deposition of nitrogen.
Keywords: Long-range transport; Sulfur dry deposition; Nitrogen dry deposition; K-mean clustering technique; Emission amount in East Asia;

This study develops a theory for the Gaussian plume equation to account for the formation of secondary sulfate aerosol and nitrate aerosol from the oxidations of gaseous SO2 and NO x emissions. In addition, the mechanisms of scavenging, dry deposition, background pollutant transport and subsidence from the top planetary boundary layer are also considered. A Gaussian trajectory transfer-coefficient model (GT x ) has been developed. Wind vector, stability class and mixing height among each time interval along a trajectory are allowed to change. Quantification on the source/receptor relationship of primary pollutants and the secondary aerosols from sources can be determined in a single model run. Nonetheless, it should be noted that the current formulation depends on the explicit description of the oxidation rates of gaseous SO2 and NO x . Since reactive chemistry, in general, is nonlinear, this would be the limitation of the approach. Alternatively, prior to application of the model to a site, the rates calibrated to specific time and the location of interest are suggested.
Keywords: Secondary aerosol; Sulfate; Nitrate; Gaussian plume; Particulate matter; Inverse approach;

Quantification on the source/receptor relationship of primary pollutants and secondary aerosols by a Gaussian plume trajectory model: Part II. Case study by Ben-Jei Tsuang; Chien-Lung Chen; Chung-Hsien Lin; Man-Ting Cheng; Ying-I Tsai; Chia-Pin Chio; Rong-Chang Pan; Pei-Hsuan Kuo (3993-4006).
This study applies a newly developed model, the Gaussian trajectory transfer-coefficient model (GTx) (Part I, Atmos. Environ., this issue), to Taichung City. Two fossil-fueled power plants are situated in the vicinity of Taichung City. The model was calibrated in the winter of 1997 and verified throughout the entire following year of 1998. The results indicate that the correlation coefficients (r 2) for the daily concentrations of various pollutants were in the range of 0.49–0.83 during the calibrated period and in the range of 0.37–0.71 during the verification period. The advantage of GTx is that the source/receptor relationship of sources can be determined in a single model run. It shows that line sources contributed to 62% of CO, 65% of NO x and 21% of nitrate aerosol; point sources contributed to 46% of SO2, 57% of sulfate aerosol and 27% of PM2.5; and area sources contributed to 18% of PM2.5 and 60% of PM2.5–10 during the PM10 episodes in 1998. During the episodes TC power plant contributed to more fractions of pollutants than during non-episode days since the sea breeze blew its plume to the city. According to our analysis, if a fossil-fueled power plant is built at 1–3 days upwind of a city with NO x emitted from an effective stack height within 100–800 m, it has a higher potential to deteriorate the air quality of the city by increasing the concentration level of nitrate aerosols under unfavorable meteorological conditions.
Keywords: Secondary aerosol; Sulfate; Nitrate; Gaussian plume; Particulate matter; Source/receptor relationship;

Characteristics of pollutants at heights in the top of the Planetary Boundary Layer (PBL) are collected and used in a local-scale model. A subsidence mechanism is developed to quantify the concentration fraction from the top PBL to simulate PM concentration during Asian dust-storm (ADS) periods. The results show that using the data measured at a mountain station, which is very vulnerable to ADS, as the top boundary conditions for the air quality model can capture all the PM2.5 episodes due to local sources and ADS events, at a low-altitude urban station. The correlation coefficient (r 2) of daily PM2.5−10 concentration has increased from 0.17 to 0.62 by incorporating the subsidence mechanism, and that of PM2.5 increases as well. The model results of nitrate, sulfate and ammonium aerosol in fine radii can be compared with observations. According to our analysis, five out of eight PM2.5 or PM10 episode days occurred on ADS days in the past 4 years (1999–2002). During ADS episodes in 2000, 12% of PM2.5 and 53% of PM2.5−10 were from ADS dust. In addition, two dry deposition algorithms are evaluated; the algorithm of Seinfeld and Pandis (Atmospheric Chemistry and Physics from Air Pollution to Climate Change, Wiley, New York, 1998, 1057pp.) is suggested in this case study.
Keywords: Yellow sand; Kosa; Subsidence; Atmospheric aerosol; Chemical characterization; Gaussian plume;

Aircraft and surface observations of air quality in Puget Sound and a comparison to a regional model by Julie A Snow; James B Dennison; Daniel A Jaffe; Heather U Price; Joseph K Vaughan; Brian Lamb (4019-4032).
Three research flights were conducted during August 2001 as part of the PNW2001 field study in the Puget Sound region. Each flight presented a case study of unique sources, meteorological conditions, and spatial distributions of pollutants. On 10 August, an urban smog episode was sampled downwind of the Puget Sound Seattle–Vancouver corridor containing high mixing ratios of O3 (∼80 ppbv) and high aerosol scattering coefficients (σ sp) (∼35 M m−1). The ozone and σ sp measured during this flight were typical of summer pollution events in the Puget Sound region. The AIRPACT forecast model (MM5–CALMET-CALGRID) showed variable results when compared to surface measurements. In addition, predicted surface O3 maxima were several hours too early and fell off sharply relative to observations. AIRPACT generally under-predicted upper-level O3 concentrations and misplaced the observed O3 maxima. On 16 August, a second pollution region was encountered in a broad layer between 2 and 4.5 km above a well-defined temperature inversion. Meteorological analysis and satellite imagery suggest the high O3 mixing ratios (60 ppbv) and very high σ sp (80 M m−1) were from fires burning in Washington, Oregon, and Northern California. IMPROVE aerosol chemistry data from sites in the Cascade Mountains showed evidence of biomass burning emissions reaching the surface 2 days prior to this flight. The last flight, on 20 August, sampled slightly polluted background conditions in the region. Ozone levels reached only 30 ppbv and σ sp reached 20 M m−1 at the surface, but was much lower aloft. Therefore, this flight was representative of background conditions during the summer in this region. The results from these research flights provide evidence of enhanced O3 and σ sp, extending to 4 km altitude over Puget Sound, during the summer months from varying sources. They further demonstrate the current capability of the AIRPACT O3 forecast system and, in one case, illustrate the need to include biomass-burning emissions in the model forecasts.
Keywords: Ozone; O3; Aerosols; Biomass burning; Urban pollution; Air quality; Regional model; AIRPACT; Atmospheric chemistry; Pacific Northwest; PNW2001;

New Directions: Atmospheric Brown “Clouds” by V. Ramanathan; P.J. Crutzen (4033-4035).