Atmospheric Environment (v.38, #19)

Assessment of wintertime atmospheric pollutants in an urban area of Kansai, Japan by Chang-Jin Ma; Yoshishige Oki; Susumu Tohno; Mikio Kasahara (2939-2949).
An intensive measurement of particulate matter and gaseous materials was made to assess the characteristics of wintertime atmospheric pollutants in an urban area of Kansai, Japan. Sampling was performed by a combination of filter pack sampler and low-pressure Andersen impactor (LPAI). Particle-induced X-ray Emission (PIXE) and Thermal/Optical Reflectance (TOR®) methods were employed in analyzing element and carbon, respectively. The concentrations of SO2, NO x , and PM2.5 monitored during our intensive measurement show a strong time serial variation. PM2.5 levels are higher in the daytime with an average level of 21.3 μg m−3. Most of the peaks for NO x were regularly found in the morning throughout the campaign duration. The number concentration of particles larger than 0.3 μm appears dominated by the ultrafine particles ranged between 0.3 and 0.5 μm. The size distribution of elemental concentration as a function of water solubility was investigated. Organic carbon (OC) concentration shows the strong size distribution with the main peak formed in a range of 0.29–0.67 μm, while elemental carbon (EC) is principally enriched in a range of 0.12–0.29 μm ultra fine fraction. TC (OC+EC) fraction accounts for 42.5% and 26.2% of the mass concentration in fine particle fraction (<1.17 μm ) and coarse particle fraction (>1.17 μm), respectively. The simulated backward aerosol dispersion with the surface wind roses for three events of high PM2.5 mass concentration indicates that aerosol dispersions might be originated from the emission sources of Osaka and Shiga. Also the possibility of long-range transportation of fine particulate matter from the domestic areas of Japan, Taiwan, and Pacific Ocean was still raised. The result of factor analysis indicates that automobile exhaust, fossil fuel combustion, refuse incineration, iron industry, and soil originated particles contribute the major portion of PM2.5 in our sampling area.
Keywords: Particulate matter; Source profile; PIXE; Wintertime; Carbon; Aerosol dispersion;

To determine the physicochemical properties of individual solid particles retained in raindrops, the size-segregated raindrop sampling was carried out at ground-based site in Kyoto, Japan in Asian dust storm event during ACE-Asia. For the analysis of elemental components in individual solid particles, X-ray fluorescence microprobe system installed at Super Photon ring 8 GeV (SPring-8) BL-37XU was applied. Consequently interraindrop data of individual solid particles that are present inside the raindrops could be obtained. The number size distribution of individual solid particles scavenged by each raindrop size was compared to the calculated particle-scavenging coefficient (E). There was a good agreement between the calculated scavenging coefficient for particles and the measured number size distribution of particles with radius 1 μm. Elemental mass showing the peak at raindrops collected on 0.7 mm mesh size was varied as a function of raindrop size. The masses of crustal components and chlorine show significantly high level regardless of raindrop size. Individual residual particles were successfully classified into several factors as a function of raindrop size. The hygroscopic portions for S, Cl, K, and Ca in individual particles retained in size-segregated raindrop were determined. The mixed particles with crustal and sea-salt accounted for large fraction of particles retained in small raindrops. Whereas, in the case of large raindrops, the mixed residual particles with crustal and sulfur contributed to large portion. The results obtained from our study indicate that a large number of dust particles were incorporated into cloud droplets during their long-range transport and dust particles were effectively washed out by raindrops during rainfall event.
Keywords: Asian dust storm; ACE-Asia; Size-resolved raindrop; Residual particle; Scavenge; Wet deposition;

Characteristics of aerosol acidity in Hong Kong by Ravi Kant Pathak; Peter K.K. Louie; Chak K. Chan (2965-2974).
The ammonium-to-sulfate ratio ([NH4 +]/[SO4 2−]) and the strong acidity have been generally used as parameters to describe the acidic nature of atmospheric aerosols. However, both parameters do not provide the in situ acidic characteristics of atmospheric aerosols, which are more relevant to the reactivity and the environmental impacts of the aerosols. In this study, the in situ free acid concentrations and the in situ pH of aerosols are investigated to understand the acidic characteristics of atmospheric aerosols in Hong Kong (HK). Over 182 datasets on 24 h Respirable Suspended Particles (RSP) samples collected in 2001 from seven air-quality-monitoring sites run by the Hong Kong Environmental Protection Department are analyzed. Simulations using the Aerosol Inorganic Model (AIM2) reveal that the in situ acidity, i.e., the free acid concentration ([H+]free), is only a minor fraction (∼23%) of the estimated strong acidity in the fine particles because of the presence of bisulfate ions. The acidity characteristics of fine particles are a function of mainly RH and ammonium to sulfate ratio. The in situ free acid concentration, the normalized water content ([H2O]AIM2/[SO4 2−]), and the dissociation of bisulfate to free acid in the aerosols decrease as the [NH4 +]/[SO4 2−] ratio increases and the Relative Humidity (RH) decreases. The acidic fine mode particles have average molar [NH4 +]/[SO4 2−] ratio of 1.42, strong acidity of 51 nmol m−3, in situ acidity of 11 nmol m−3, and in situ pH of 0.25 on average. Our findings suggest that even the more neutralized ([NH4 +]/[SO4 2−] >1.5) particles, such as those found when HK is under the influence of continental air masses from the Chinese mainland, can have high in situ acidity and low pH when the RH is low. This study calls for more investigation of the acidity of aerosols in HK, incorporating the concepts of in situ acidity and pH.
Keywords: pH; Water content; Aerosol thermodynamics; Sulfate; Ammonium; RSP; PM10; PM2.5;

Transport of atmospheric carbon monoxide, ozone, and hydrocarbons from Chinese coast to Okinawa island in the Western Pacific during winter by Shungo Kato; Yoshizumi Kajii; Ryunosuke Itokazu; Jun Hirokawa; Seiichiro Koda; Yoshikatsu Kinjo (2975-2981).
CO, O3, and hydrocarbon measurements were conducted at Okinawa island, a southern Japanese island, during winter in 2000. The observed air was affected by the pollution transported from Chinese coastal area. Hydrocarbon concentration decreased as carbon number increased. This indicated that the measurement site was not affected by local anthropogenic sources. But negative correlation between O3 and sporadically high CO was observed. This indicated the fast transportation of polluted air from source region. Backward trajectory analyses showed that the air mass came from Chinese coastal area contained higher concentration of hydrocarbons than other trajectory categories. Transport time from source area to the observatory and observed hydrocarbon concentrations had negative correlations. The observed data at Okinawa were compared with the result obtained at Ogasawara island, a more remote island in the Western Pacific, in 1999. Their distance from the continent were different, however, the way of hydrocarbon decrease was same manner at these two sites. The standard deviation of the log natural of the mixing ratio for many hydrocarbons had more deviation at Okinawa than at Ogasawara. This indicated that Okinawa was more affected by polluted air which transported from the source region than Ogasawara.
Keywords: Long range transport; Continental out flow; East Asia; Western Pacific; Air pollution;

Ambient particulate matter mass concentrations were measured in terms of PM1 and PM1−10 for 8 months in 2000–2001, at a sampling site in the urban city of Kaohsiung, Taiwan. On average for the 8-month samples, 52±20% of the PM10 was made up of PM1. The concentration of particulate n-alkanes was in the range of 75–265 ng m−3 in PM1 and 89–346 ng m−3 in PM10, considerably higher than the concentration levels measured at other urban areas. The mass content of n-alkanes in ambient submicron aerosol particles (PM1)(0.38%) was statistically higher than that in PM1−10 (0.13) and suggests that the n-alkanes exist mainly in PM1 in Kaohsiung city. The concentration ratio of the homologues (C19–C33) of alkanes indicated that homologues were associated with submicron particles in general and that there was a high level of fractions (0.87±0.09 for C19) in PM1 for low carbon n-alkanes than for high carbon n-alkanes (0.64±0.09 for C33). For all the collected samples in this study, the average and standard deviation of CPI (carbon preference index) was 1.26±0.17 for PM1 and 1.39±0.28 for PM1−10. The plant wax contributions to the total alkanes for PM1 and PM1−10 were estimated to be 13.4% (5.9–21.7%) and 17.1% (4.8–32.0%), respectively. These observed results suggest that the organic matter in the submicron aerosol particles (PM1) in Kaohsiung city contained compounds that were predominantly contributed by anthropogenic sources with only a minor contribution from biogenic sources.
Keywords: Urban aerosols; Submicron particles (PM1); n-Alkanes; Carbon preference index (CPI); Source apportionment;

The spatial variability of aerosol number and mass along roads was determined in different regions (urban, rural and coastal-marine) of the Netherlands. A condensation particle counter (CPC) and an optical aerosol spectrometer (LAS-X) were installed in a van along with a global positioning system (GPS). Concentrations were measured with high-time resolutions while driving allowing investigations not possible with stationary equipment. In particular, this approach proves to be useful to identify those locations where numbers and mass attain high levels (‘hot spots’). In general, concentrations of number and mass of particulate matter increase along with the degree of urbanisation, with number concentration being the more sensitive indicator. The lowest particle numbers and PM1-concentrations are encountered in a coastal and rural area: <5000 cm−3 and 6 μg m−3, respectively. The presence of sea-salt material along the North-Sea coast enhances PM>1-concentrations compared to inland levels. High-particle numbers are encountered on motorways correlating with traffic intensity; the largest average number concentration is measured on the ring motorway around Amsterdam: about 160 000 cm−3 (traffic intensity 100 000 veh day−1). Peak values occur in tunnels where numbers exceed 106  cm−3. Enhanced PM1 levels (i.e. larger than 9 μg m−3) exist on motorways, major traffic roads and in tunnels. The concentrations of PM>1 appear rather uniformly distributed (below 6 μg m−3 for most observations). On the urban scale, (large) spatial variations in concentration can be explained by varying intensities of traffic and driving patterns. The highest particle numbers are measured while being in traffic congestions or when behind a heavy diesel-driven vehicle (up to 600×103  cm−3). Relatively high numbers are observed during the passages of crossings and, at a decreasing rate, on main roads with much traffic, quiet streets and residential areas with limited traffic. The number concentration exhibits a larger variability than mass: the mass concentration on city roads with much traffic is 12% higher than in a residential area at the edge of the same city while the number of particles changes by a factor of two (due to the presence of the ultrafine particles (aerodynamic diameter <100 nm). It is further indicated that people residing at some 100 m downwind a major traffic source are exposed to (still) 40% more particles than those living in the urban background areas.
Keywords: Mobile measurements; Spatial variability; Traffic; Aerosol; PM1; PM>1; CPC; LAS-X;

There is a need for robust methods for measuring ammonia emission rates from livestock buildings and manure stores, to guide efforts to abate emissions from livestock farming.All three of the measurement techniques were validated at a building section simulating a naturally ventilated (space-boarded) cattle house, with the external tracer ratio method also being validated at a simulated slurry store.In the validation tests on the external tracer ratio method the derived ammonia emission rates from the slurry store and cattle house validation studies were 25% below and 43% above the measured release rate, respectively. These biases were shown by t-tests to be statistically highly significant, but no clear explanation could be found for the different signs and magnitudes in the two cases. For the ITR method, recovery rates of 78% and 101% of released NH3 were achieved, with low and high release rates, respectively.Validation tests conducted on the flux samplers gave an average of 66% (standard deviation 2.9%) ammonia recovery. The cause of this non-ideal level of recovery has not yet been identified. However, given the low standard deviation, it was concluded that these samplers could be used to measure ammonia emission rates from real farm buildings, provided that a correction factor for the non-ideal recovery was applied.
Keywords: Ammonia; Sulphur hexafluoride; Emission rate; Livestock; Tracer gas;

Measuring ammonia emission rates from livestock buildings and manure stores—part 2: Comparative demonstrations of three methods on the farm by C.J. Dore; B.M.R. Jones; R. Scholtens; J.W.H.Huis in’t Veld; L.R. Burgess; V.R. Phillips (3017-3024).
Comparative demonstrations of three methods (flux sampling, external tracer ratio, and internal tracer ratio), were mounted in four real farm situations. A flux sampling method was demonstrated at a commercial dairy cow house (slurry-based), at a commercial piggery (straw-based), at a full-scale above-ground cylindrical slurry store (dairy cow slurry) and a full-scale earth-bank lagoon (pig slurry). An external tracer ratio method was demonstrated, in parallel with the flux sampling method, at the dairy cow house and at the above-ground slurry store. An internal tracer ratio method was demonstrated at the dairy cow house only. At the dairy cow house, the corrected emission rates from the flux sampling method and from the external tracer ratio method agreed to within the estimated experimental range, while the emission rate from the internal tracer ratio method was significantly lower.The overall conclusion of the study is that all three methods can have a useful role, the choice of which to deploy depending on the particular measurements needed in each case. The paper includes a table (No. 7) which indicates which is the recommended method when each of various considerations has top priority.
Keywords: Ammonia; Emission rate; Method; Livestock building; Manure store;

Investigation of sources of atmospheric aerosol at urban and semi-urban areas in Bangladesh by Bilkis A. Begum; Eugene Kim; Swapan K. Biswas; Philip K. Hopke (3025-3038).
Samples of fine and coarse fractions of airborne particulate matter (PM) were collected in a semi-residential (AECD) area from June 2001 to June 2002 of Dhaka and in an urban area of Rajshahi, a city in northwestern region of Bangladesh from August 2001 to May 2002. The samples were collected using a ‘Gent’ stacked filter sampler in two fractions of < 2.5 μm fine and 2.5–10 μm coarse sizes. The samples were analyzed for elemental concentrations by PIXE. The data sets were then analyzed by positive matrix factorization technique to identify the possible sources of atmospheric aerosols in these areas. The best solutions were found to be six and seven factors for elemental compositions for coarse and fine PM fractions in semi-residential Dhaka and five factors for elemental compositions of each of the coarse and fine PM respectively in the urban area of Rajshahi. The sources are soil dust, road dust, cement, sea salt, motor vehicles and biomass burning. The PMF results show that a large fraction of about more than 50% of the PM2.5–10 mass at both sites comes from soil dust and road dust. The motor vehicle including two strokes contributes about 48% of the PM2.5 mass in case of semi-residential area Dhaka. On the other hand, the biomass-burning factor contributes about 50% of the PM2.5 mass in Rajshahi.
Keywords: Receptor modeling; Positive matrix factorization; Bangladesh; PM2.5; PM10–2.5; Ambient aerosol composition;

A three-dimensional computational fluid dynamics model with the renormalization group kε turbulence scheme is developed. The model developed is used to investigate the effects of ambient wind direction on flow and dispersion around a group of buildings. According to the ambient wind direction, three flow patterns are identified in a view of the characteristics of the mean flow circulation generated in street canyons. In the first flow pattern, a portal vortex generated behind the east wall of the upwind building is symmetric about the center of the street canyon. In the second flow pattern, a portal vortex is also generated behind the east wall of the upwind building, but its horizontal axis is not perpendicular to the ambient wind direction. In the third flow pattern, the footprints of a portal vortex are located behind both the east and north walls of the upwind building. When the incident wind angle is 45°, flow is diagonally symmetric behind the upwind building. As the incident wind angle increases, pollutant escape from the street canyons decreases. Except for the case where the ambient wind direction is perpendicular to the buildings, pollutants are trapped in the portal vortex, thus exhibiting high concentration there.
Keywords: Computational fluid dynamics; RNG kε turbulence model; Urban flow and dispersion; Urban street canyon; Ambient wind direction;

A brown haze, which builds up over Auckland, New Zealand under calm and cold weather conditions, causes public concern. This study identifies the major sources of this brown haze using variations in the elemental composition of airborne particulate matter between those collected during brown haze days, and normal days in the year 2001. Airborne particulate matter was collected in a site in southeast Auckland, using a versatile air pollution sampler (VAPS) and a PM10 hi-volume sampler. The elemental composition of the samples, collected using the hi-volume sampler, was quantitatively determined for 14 elements using ICP/MS. The elemental composition of the coarse and fine fractions of the particulate matter collected using the VAPS, was quantitatively determined using ion beam analysis for 16 elements. Elemental carbon was quantitatively determined by a light reflection/transmission technique. For source determination, the VAPS was found to be more useful that the hi-volume sampler.Enrichment factors (EF) for each element of the PM10 samples were calculated to identify the sources. Further, principal component factor analysis with Varimax rotation was performed using some selected elements in the coarse and fine fractions of particulate samples collected using the VAPS to identify major sources of PM10 in Auckland. The analysis yielded six significant sources: sea spray, suspended soil/road dust, fine soil, domestic emissions, diesel, and petrol emissions. EF values for brown haze samples revealed that diesel emissions were the major sources responsible for the build-up of brown haze. Coal combustion emissions were also found to contributed, but to a lesser extent. Furthermore, source apportionment using absolute principal component analysis on brown haze and normal days confirmed that accumulation of diesel emissions contributed most to the appearance of brown haze and coal combustion emissions to a lesser extent.
Keywords: Airborne particulate matter; PM10 hi-volume sampler; Versatile air pollution sampler (VAPS); ICP/MS; Ion beam analysis (IBA); Factor analysis;

Regional Sr–Nd isotopic ratios of soil minerals in northern China as Asian dust fingerprints by Takanori Nakano; Yoriko Yokoo; Masataka Nishikawa; Hideaki Koyanagi (3061-3067).
We report that arid soils in various areas of northern China can be distinguished by using Sr–Nd isotopic ratios of acid-resistant minerals and Sr isotopic ratios of water- and weak-acid-soluble minerals. Our results show that contemporary dust falling on Beijing is transported mainly from the adjacent northwestern to western areas and is more likely to be related to desertification than dust from the remote Takla Makan desert, the southwestern Gobi desert, or the Loess Plateau. Mineral isotope fingerprinting of arid soils is a powerful tool for source identification and impact assessment of mineral dust, and can serve as a desertification index.
Keywords: Asian dust sources; Provenance-derived mineral; Salinization mineral; Beijing; Desertification; China;

The weekend effect on ozone, a phenomenon with high ozone concentration at weekend, was analyzed using the data measured at 7 photochemical assessment monitoring stations (PAMS), (1) volatile organic compounds (VOCs) monitoring station and (2) routine ambient air quality monitoring stations in southern California during ozone season from 1995 to 2001. Weekend/weekday differences of ozone, ozone precursors and PM10 concentrations and the light scatter, composition and reactivity of VOCs in morning traffic rush time and afternoon peak ozone time were compared. The possible causes for the weekend effect were discussed. The significant weekend effect was observed in southern California except in areas close to beach and far downwind direction from L.A. Downtown. On average, the peak O3 and max 8 h average O3 concentrations at weekend were 20% and 22%, respectively, higher than those on weekday while the concentrations of O3 precursors and PM10 and the light scatter were lower at weekday in southern California. In morning traffic rush time, the average concentrations of NO x , CO, NMOC and PM10 and the light scatter at weekend were about 37%, 18%, 15%, 14% and 9%, respectively, lower than those on weekday. In afternoon peak ozone time, the average concentrations of NO x , CO, NMOC and PM10 and the light scatter at weekend were about 29%, 13%, 24%, 17% and 17%, respectively, lower than those on weekday. The reactivities of VOCs in morning traffic rush time and afternoon peak ozone time at weekend were 17% and 26%, respectively, lower than those on weekday. VOCs sensitivity for ozone formation and a decrease NO x emissions at weekend can well explain the weekend effect in southern California. Less scatter of sunlight due to lower fine particle concentration at weekend results in enhanced ozone formation might be another possible cause for the weekend effect.
Keywords: O3; Weekend effect; Precursors; VOCs reactivity;

Monoterpene emissions from a Pacific Northwest Old-Growth Forest and impact on regional biogenic VOC emission estimates by Shelley Pressley; Brian Lamb; Hal Westberg; Alex Guenther; Jack Chen; Eugene Allwine (3089-3098).
Measurements of natural hydrocarbon emission rates are reported for an old-growth Pacific Northwest coniferous forest. The emission data were collected for the two dominant species Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) during the growing season in 1997 and 1998 using branch enclosure techniques. Samples were collected at different heights from 13 to 51 m within the canopy using the Wind River Canopy Crane facility. The standard emission factor at a temperature of 30°C and the temperature coefficient for Douglas-fir is E s=0.39±0.14 μg C g−1  h−1 and β=0.14±0.05°C−1 and for western hemlock E s=0.95±0.17 μg C g−1  h−1 and β=0.06±0.02°C−1. There was considerable variability among all the emission factors due to seasonal and branch-to-branch variations. Within season emission factors appear to decline from May to September for the Douglas-fir, although there was no corresponding decrease for the western hemlock. There was no significant difference in standard emission factors (E s) or temperature coefficients as a function of sunlit versus shady growth environment (different heights) for Douglas-fir, but western hemlock emission samples collected low in the canopy showed no exponential correlation with temperature. Applying the standard emission factors from this study to a Pacific Northwest domain and comparing the modified emission inventory to the current regulatory-based emission inventory yielded a net decrease of 19% in the domain wide monoterpene emissions. The relatively small difference in biogenic emissions is slightly misleading, as the difference in standard emission rates between this study and current regulatory rates is quite significant, and they offset each other when combined in this domain. When this inventory was input into a regional photochemical air quality simulation using the MM5/CMAQ system, the reduction in biogenic emissions resulted in an insignificant decrease of O3 and a significant decrease in the secondary organic aerosol (domain wide −20%). The emission measurements reported here represent one of the first extensive data sets for an old-growth forest, where sampling conditions are limited to in situ enclosure techniques within the tall, elevated canopy.
Keywords: Douglas-fir; Western hemlock; Enclosure method; Secondary biogenic aerosol; Ozone;