Seasonal variations of acidic air pollutants in Seoul,South Korea

The annular denuder system (ADS) was used to characterize seasonal variations of acidic air pollutants in Seoul, South Korea. Fifty- four 24 h samples were collected over four seasons from October 1996 to September 1997. The annual mean concentrations of HNO₃, HNO₂, SO₂ and NH₃ in the gas phase were 1.09, 4.51, 17.3 and 4.34 μg m^-3, respectively. The annual mean concentrations of PM_2.5(d_p≤2.5 μm in aerodynamic diameter, 50% cutoff), SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were 56.9, 8.70, 5.97 and 4.19 μg m^-3, respectively. All chemical species monitored from this study showed statistical seasonal variations. Nitric acid (HNO₃) and ammonia (NH₃) exhibited substantially higher concentrations during the summer, while nitrous acid (HNO₂) and sulfur dioxide(SO₂) were higher during the winter. Concentrations of PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were higher during the winter months. SO^2-₄, NO^-₃ and NH⁺₄ accounted for 26–38% of PM_2.5. High correlations were found among PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄. The mean H⁺ concentration measured only in the fall was 5.19 nmole m^-3.     

The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite,Taiwan

The characteristics of ambient aerosols, affected by solar radiation, relative humidity, wind speed, wind direction, and gas–aerosol interaction, changed rapidly at different spatial and temporal scales. In Taipei Basin, dense traffic emissions and sufficient solar radiation for typical summer days favored the formation of secondary aerosols. In winter, the air quality in Taipei Basin was usually affected by the Asian continental outflows due to the long-range transport of pollutants carried by the winter monsoon. The conventional filter-based method needs a long time for collecting aerosols and analyzing compositions, which cannot provide high time-resolution data to investigate aerosol sources, atmospheric transformation processes, and health effects. In this work, the in situ ion chromatograph (IC) system was developed to provide 15-min time-resolution data of nine soluble inorganic species (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). Over 89% of all particles larger than approximately 0.056 μm were collected by the in situ IC system. The in situ IC system is estimated to have a limit of detection lower than 0.3 μg m⁻³ for the various ambient ionic components. Depending on the hourly measurements, the pollutant events with high aerosol concentrations in Taipei Basin were associated with the local traffic emission in rush hour, the accumulation of pollutants in the stagnant atmosphere, the emission of industrial pollutants from the nearby factories, the photochemical secondary aerosol formation, and the long-range transport of pollutants from Asian outflows.     

Chemical characteristics of atmospheric aerosols over southwest coast of India

Ambient aerosol samples, collected from Mangalore region in the southwest coast of India during the period of late winter (February and March) to early summer (April and May), have been analysed for water-soluble ionic species. Their abundance pattern is dominated by HCO₃⁻, SO₄²⁻, Na⁺, Cl⁻, with minor contribution from NO₃⁻, Ca²⁺, NH₄⁺, K⁺ and Mg²⁺ indicating the contribution from not only sea salt, but also from anthropogenic and dust sources; with pronounced seasonal variability. The suspended particulate matter concentration varied from 35 to 160 μg m⁻³, with consistently higher values during the late winter. Back trajectory analysis suggests the origin of the air masses shifting from Indo-Gangetic Plains (during late winter) to those from the Arabian Sea and the area around Persian Gulf during April–May. Air masses passing over Northern India (Indo-Gangetic Plains) impart characteristic contribution of ionic species from fossil fuel combustion, biomass burning and eolian dust as asserted by the factor analysis. A detailed study on characterisation of aerosols from south Asian region is rather sparse but essential for modelling the effect of tropospheric aerosols on climate.     

Identification,abundance and seasonal variation of anthropogenic organic aerosols from a mega-city in China

PM_2.5 aerosols were collected in Nanjing, a typical mega-city in China, during summer and winter 2004 and were characterized for aromatic and cyclic compounds using a GC/MS technique to understand the air pollution problem. They include polycyclic aromatic hydrocarbons (PAHs), hopanes, phthalates and hydroxy-PAHs (OH-PAHs). PAHs, hopanes and OH-PAHs presented higher concentrations in winter (26–178, 3.0–18, and 0.013–0.421 ng m⁻³, respectively) than in summer (12–96, 1.6–11, and 0.029–0.171 ng m⁻³, respectively) due to an enhanced coal burning for house heating and atmospheric inversion layers developed in the cold season. In contrast, phthalates are more abundant in summer (109–368 ng m⁻³, average 230 ng m⁻³) than in winter (33–390 ng m⁻³, average 170 ng m⁻³) due to an enhanced evaporation from plastics during the hot season and the subsequent deposition on the pre-existing particles. Generally, all the identified compounds showed higher concentrations in nighttime than in daytime due to inversion layers and increased emissions from heavy-duty trucks at night. PAHs, hopanes and phthalates in Nanjing aerosols are 5–100 times more abundant than those in Los Angeles, USA, indicating a serious air pollution problem in the city. Concentrations of OH-PAHs are 1–3 orders of magnitude less than their parent PAHs and comparable to those reported from other international cities. Source identification using diagnostic ratios of the organic tracers suggests that PAHs in Nanjing urban area are mainly derived from coal burning, whereas hopanes are more attributable to traffic emissions.     

Long-term measurements of SO2 dry deposition over Gansu Province,China

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.     

Speciated mercury in size-fractionated particles in Shanghai ambient air

Size-fractionated particles were collected at two sites from July 2004 to April 2006 in Shanghai. The mercury in particles was extracted and divided operationally into four species: exchangeable particulate mercury (EXPM), HCl-soluble particulate mercury (HPM), elemental particulate mercury (EPM) and residual particulate mercury. The total particulate Hg concentration during the study period ranged from 0.07 ng m^?3 to 1.45 ng m^?3 with the average 0.56 ± 0.22 ng m^?3 at site 1, while 0.20 ng m^?3–0.47 ng m^?3 with the average 0.33 ± 0.09 ng m^?3 at site 2, which is far higher than some foreign cities and comparable to some cities with heavy air pollution in China. The Hg mass content also displayed evident size distribution, with higher value in PM_1.6–3.7, somewhat higher or lower than the source profile. EXAM was only found in the summer, HPM have higher percentage in summer and fall rather than in winter and spring. The different mercury species showed different correlation to temperature, relative humidity, wind speed. HPM positively depends on temperature at both sites which implies the importance of mercury transformation on particles. In foggy days TPM increased greatly, but HPM didn't vary greatly as anticipated. Instead, RPM gained a distinguished increase. It demonstrated that aqueous reaction and complex heterogenic reactions in droplet might happen in acidic environment. The correlation of mercury with other pollutants including SO₂, NO₂, CO and PM₁₀ varies with the different mercury forms. Hybrid single-particle lagrangian integrated trajectories (HYSPLIT) model was used to back trace air mass at different representative days and results indicated that transportation from Huabei Plain will increase mercury concentration in winter and fall to some extent. The possible existing compounds and their atmospheric behavior of HPM, EPM and RPM were calculated and the compared to analyze its implication on atmospheric mercury cycle.     

Particulate matter in the indoor air of classrooms—exploratory results from Munich and surrounding area

Numerous epidemiological studies have demonstrated the association between particle mass (PM) concentration in outside air and the occurrence of health related problems and/or diseases. However, much less is known about indoor PM concentrations and associated health risks. In particular, data are needed on air quality in schools, since children are assumed to be more vulnerable to health hazards and spend a large part of their time in classrooms.On this background, we evaluated indoor air quality in 64 schools in the city of Munich and a neighbouring district outside the city boundary. In winter 2004–2005 in 92 classrooms, and in summer 2005 in 75 classrooms, data on indoor air climate parameters (temperature, relative humidity), carbon dioxide (CO₂) and various dust particle fractions (PM₁₀, PM_2.5) were collected; for the latter both gravimetrical and continuous measurements by laser aerosol spectrometer (LAS) were implemented. In the summer period, the particle number concentration (PNC), was determined using a scanning mobility particle sizer (SMPS). Additionally, data on room and building characteristics were collected by use of a standardized form. Only data collected during teaching hours were considered in analysis. For continuously measured parameters the daily median was used to describe the exposure level in a classroom.The median indoor CO₂ concentration in a classroom was 1603 ppm in winter and 405 ppm in summer. With LAS in winter, median PM concentrations of 19.8 μg m⁻³ (PM_2.5) and 91.5 μg m⁻³ (PM₁₀) were observed, in summer PM concentrations were significantly reduced (median PM_2.5=12.7 μg m⁻³, median PM₁₀=64.9 μg m⁻³). PM_2.5 concentrations determined by the gravimetric method were in general higher (median in winter: 36.7 μg m⁻³, median in summer: 20.2 μg m⁻³) but correlated strongly with the LAS-measured results. In explorative analysis, we identified a significant increase of LAS-measured PM_2.5 by 1.7 μg m⁻³ per increase in humidity by 10%, by 0.5 μg m⁻³ per increase in CO₂ indoor concentration by 100 ppm, and a decrease by 2.8 μg m⁻³ in 5–7th grade classes and by 7.3 μg m⁻³ in class 8–11 compared to 1–4th class. During the winter period, the associations were stronger regarding class level, reverse regarding humidity (a decrease by 6.4 μg m⁻³ per increase in 10% humidity) and absent regarding CO₂ indoor concentration. The median PNC measured in 36 classrooms ranged between 2622 and 12,145 particles cm⁻³ (median: 5660 particles cm⁻³).The results clearly show that exposure to particulate matter in school is high. The increased PM concentrations in winter and their correlation with high CO₂ concentrations indicate that inadequate ventilation plays a major role in the establishment of poor indoor air quality. Additionally, the increased PM concentration in low level classes and in rooms with high number of pupils suggest that the physical activity of pupils, which is assumed to be more pronounced in younger children, contributes to a constant process of resuspension of sedimented particles. Further investigations are necessary to increase knowledge on predictors of PM concentration, to assess the toxic potential of indoor particles and to develop and test strategies how to ensure improved indoor air quality in schools.     

Multi-year hourly PM2.5 carbon measurements in New York: Diurnal,day of week and seasonal patterns

Multi-year hourly measurements of PM_2.5 elemental carbon (EC) and organic carbon (OC) from a site in the South Bronx, New York were used to examine diurnal, day of week and seasonal patterns. The hourly carbon measurements also provided temporally resolved information on sporadic EC spikes observed predominantly in winter. Furthermore, hourly EC and OC data were used to provide information on secondary organic aerosol formation. Average monthly EC concentrations ranged from 0.5 to 1.4 μg m^?3 with peak hourly values of several μg m^?3 typically observed from November to March. Mean EC concentrations were lower on weekends (approximately 27% lower on Saturday and 38% lower on Sunday) than on weekdays (Monday to Friday). The weekday/weekend difference was more pronounced during summer months and less noticeable during winter. Throughout the year EC exhibited a similar diurnal pattern to NO_x showing a pronounced peak during the morning commute period (7–10 AM EST). These patterns suggest that EC was impacted by local mobile emissions and in addition by emissions from space heating sources during winter months. Although EC was highly correlated with black carbon (BC) there was a pronounced seasonal BC/EC gradient with summer BC concentrations approximately a factor of 2 higher than EC. Average monthly OC concentrations ranged from 1.0 to 4.1 μg m^?3 with maximum hourly concentrations of 7–11 μg m^?3 predominantly in summer or winter months. OC concentrations generally correlated with PM_2.5 total mass and aerosol sulfate and with NO_x during winter months. OC showed no particular day of week pattern. The OC diurnal pattern was typically different than EC except in winter when OC tracked EC and NO_x indicating local primary emissions contributed significantly to OC during winter at the urban location. On average secondary organic aerosol was estimated to account for 40–50% of OC during winter and up to 63–73% during summer months.     

Comprehensive assessment of pine needles as bioindicators of PAHs using multivariate analysis. The importance of temporal trends

The importance of the annual and seasonal trends associated to the polycyclic aromatic hydrocarbons (PAHs) biomonitoring by pine needles are studied with a comprehensive use of univariate and multivariate analysis tools. For this purpose, four pine needle sampling campaigns (winter, spring, summer and autumn 2007) were carried out in 29 sites from Portugal. Needles from Pinus pinaster Ait. and Pinus pinea L. trees were collected from all year-classes available in each tree, corresponding to the different shoots of needles coming out every spring and the results of both species were treated separately. Annual trends of polycyclic aromatic hydrocarbons (PAHs) contamination indicate a general increase from the least to the most exposed year-classes, for all seasons. The mean values for the sum of 16 PAHs ranged from 71 ± 33 ng g⁻¹ (dry weight – dw) for new year (2007) needles in the summer to 514 ± 317 ng g⁻¹ (dw) for 2-year needles (2005) in the spring for P. pinea, and between 90 ± 50 ng g⁻¹ (dw) for new year (2007) needles in the summer and 1212 ± 436 ng g⁻¹ (dw) for 3-year needles (2004) in summer for P. pinaster. The seasonal evolution shows the highest concentrations in the winter, then declining to the lowest levels in the summer and rising again from summer to autumn. Principal component analysis confirmed differences between seasons and needle year-classes, more visible for P. pinea samples. The cooler seasons have more affinity towards the lighter more abundant PAHs, as do the older needles. Differences between both pine species are also evident.     

Estimates of air-sea exchange of mercury in the Baltic Sea

The concentrations of total gaseous mercury (TGM) in air over the southern Baltic Sea and dissolved gaseous mercury (DGM) in the surface seawater were measured during summer and winter. The summer expedition was performed on 02–15 July 1997, and the winter expedition on 02–15 March 1998. Average TGM and DGM values obtained were 1.70 and 17.6 ng m⁻³ in the summer and 1.39 and 17.4 ng m⁻³ in the winter, respectively. Based on the TGM and DGM data, surface water saturation and air-water fluxes were calculated. The results indicate that the seawater was supersaturated with gaseous mercury during both seasons, with the highest values occurring in the summer. Flux estimates were made using the thin film gas-exchange model. The average Hg fluxes obtained for the summer and winter measurements were 38 and 20 ng m⁻² d⁻¹, respectively. The annual mercury flux from this area was estimated by a combination of the TGM and DGM data with monthly average water temperatures and wind velocities, resulting in an annual flux of 9.5 μg m⁻² yr⁻¹. This flux is of the same order of magnitude as the average wet deposition input of mercury in this area. This indicates that reemissions from the water surface need to be considered when making mass-balance estimates of mercury in the Baltic Sea as well as modelling calculations of long-range transboundary transport of mercury in northern Europe.     

Factors influencing PM10 emissions from road pavement wear

Accelerated pavement wear is one of the major environmental disadvantages of studded tyres in northern regions and results in increased levels of PM₁₀. Measurements of PM₁₀ in a road simulator hall have been used to study the influence of pavement properties, tyre type and vehicle speed on pavement wear. The test set-up included three different pavements (one granite and two quartzite with different aggregate sizes), three different tyre types (studded, non-studded, and summer tyres) and different speeds (30–70 km h^?1). The results show that the granite pavement was more prone to PM₁₀ production compared to the quartzite pavements. Studded winter tyres yield tens of times higher PM₁₀ concentrations compared to non-studded winter tyres. Wear from summer tyres was negligible in comparison. It was also shown that wear is strongly dependent on speed; every 10 km h^?1 increase yielded an increase of the PM₁₀ concentration of 680 μg m^?3 in one of the simulator experiments.     

Characterisation of PM10 atmospheric aerosols for the wet season 2005 at two sites in East Africa

Ambient daily PM₁₀ aerosol samples were collected at two sites in Tanzania in May and June 2005 (during the wet season), and their chemical characteristics were studied. The sites were a rural site in Morogoro and an urban kerbside site in Dar es Salaam. A Gent PM₁₀ stacked filter unit sampler with sequential Nuclepore polycarbonate filters, providing fine and coarse size fractions, and a PM₁₀ sampler with quartz fibre filters were deployed. Parallel collections of 24 h were made with the two samplers and the number of these collections was 13 in Morogoro and 16 in Dar es Salaam. The average mass concentration of PM₁₀ was 27 ± 11 μg/m³ in Morogoro and 51 ± 21 μg/m³ in Dar es Salaam. In Morogoro, the mean concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were 6.8, 0.51, and 2.8 μg/m³, respectively. In contrast, higher mean concentrations (11.9, 4.6, and 3.3 μg/m³, respectively) were obtained for Dar es Salaam. At both sites, species and elements, such as black carbon, NH₄⁺, non-sea-salt SO₄^2?, K, and Ni (and at Dar es Salaam also V, As, Br, and Pb) were mainly present in the fine size fraction. The common crustal and sea-salt elements, including Na, Mg, Al, Si, Cl, Ca, Ti, Mn, Fe, and Sr, and also NO₃^? and P (and to a lesser extent Cu and Zn) were concentrated in the coarse particles. Aerosol chemical mass closure indicated that the PM₁₀ mass in Morogoro consisted, on average, of 48% organic matter (OM), 44% crustal matter, 4% sea salt, and 2% EC, while in Dar es Salaam OM, crustal matter, sea salt, and EC represented 37%, 32%, 9%, and 9% of the PM₁₀ mass. The contributions of the secondary inorganic aerosol (non-sea-salt sulphate, nitrate, and ammonium) were small, i.e., only 5% in total at each site. Carbonaceous materials and crustal matter were thus the most important components of the PM₁₀ mass. It is suggested that biomass burning is a major contributor to the OM; at Dar es Salaam there is also a very substantial contribution from traffic. A source apportionment calculation indicated that 68% of the OC at this site originated from traffic exhaust versus 32% from charcoal burning. The crustal matter at Morogoro is likely mainly attributable to soil dust resuspension, whereas in Dar es Salaam it is likely mostly resuspended road dust.     

Properties of organic matter in PM2.5 at Changdao Island,China—A rural site in the transport path of the Asian continental outflow

Fifty-five seasonal PM_2.5 samples were collected March 2003–January 2004 at Changdao, a resort island located at the demarcation line between Bohai Sea and Yellow Sea in Northern China. Changdao is in the transport path of the continental aerosols heading toward the Pacific Ocean in winter and spring due to the East Asia Monsoon. Solvent-extractable organic compounds (SEOC), organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) were analyzed for source identification based on molecular markers. This data set provides useful information for the downstream site researchers of the Asian continental outflow. Total carbon (TC, OC+EC) was ∼18 μg m⁻³ in winter, ∼9 μg m⁻³ in spring and autumn and a large part of the TC was WSOC (33% in winter, >45% in the other seasons). Winter and spring were the high SEOC seasons with n-fatty acids the highest at ∼290 and ∼170 ng m⁻³, respectively, followed by n-alkanes at ∼210 and ∼90 ng m⁻³, and polycyclic aromatic hydrocarbons (PAHs) were also at high at ∼120 and ∼30 ng m⁻³. High WSOC/TC, low C_18:1/C₁₈ of fatty acids, and low concentrations of labile PAHs such as benzo(a)pyrene, together with back trajectory analysis suggested that the aerosols were aged and transported. PAHs, triterpane and sterane distributions provided evidence that coal burning was the main source of the continental outflow. The detection of levoglucosan and β-sitosterol in nearly all the samples showed the impact of biomass burning.     

Sources and characteristics of carbonaceous aerosol in two largest cities in Pearl River Delta Region,China

PM_2.5 samples were collected at five sites in Guangzhou and Hong Kong, Pearl River Delta Region (PRDR), China in both summer and winter during 2004–2005. Elemental carbon (EC) and organic carbon (OC) in these samples were measured. The OC and EC concentrations ranked in the order of urban Guangzhou > urban Hong Kong > background Hong Kong. Total carbonaceous aerosol (TCA) contributed less to PM_2.5 in urban Guangzhou (32–35%) than that in urban Hong Kong (43–57%). The reason may be that, as an major industrial city in South China, Guangzhou would receive large amount of inorganic aerosol from all kinds of industries, however, as a trade center and seaport, urban Hong Kong would mainly receive organic aerosol and EC from container vessels and heavy-duty diesel trucks. At Hong Kong background site Hok Tsui, relatively lower contribution of TCA to PM_2.5 may result from contributions of marine inorganic aerosol and inland China pollutant. Strong correlation (R²=0.76–0.83) between OC and EC indicates minor fluctuation of emission and the secondary organic aerosol (SOA) formation in urban Guangzhou. Weak correlation between OC and EC in Hong Kong can be related to the impact of the long-range transported aerosol from inland China. Averagely, secondary OC (SOC) concentrations were 3.8–5.9 and 10.2–12.8 μg m⁻³, respectively, accounting for 21–32% and 36–42% of OC in summer and winter in Guangzhou. The average values of 4.2–6.8% for SOA/ PM_2.5 indicate that SOA was minor component in PM_2.5 in Guangzhou.     

Quantifying the sources of hazardous elements of suspended particulate matter aerosol collected in Yokohama,Japan

We analyzed metals (Mg, Al, Ca, V, Cr, Mn, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Ag, Cd, Cs, Ba, Pb and Bi), water-soluble ions (Na⁺, NH₄⁺, K⁺, Ca²⁺, Cl^?, NO₃^? and SO₄^2?) and carbonaceous mass (EC and OC) in SPM aerosol samples using an ICP-MS, ion chromatograph and CHN corder, respectively. The SPM samples were collected from 1999 to 2005 at two locations (urban site A and industrial site B) of Yokohama, Japan with concentrations in mean and ranges of 34.2 and 19.7–50.3 μg m^?3 and 22.9 and 12.7–35.1 μg m^?3 for the respective location. Source apportionment of SPM aerosol was conducted appropriately for the first time to these locations employing PCA-APCS technique. Major sources of SPM at site A were a) crustal source, b) urban origin, c) undefined, and d) mineral rock. At site B, the sources were predicted as a) urban origin, b) undefined, c) crustal source, and d) secondarily formed aerosol. The tracers and nature of the source related to urban origin at both sites were similar but retaining different source strength. Secondarily formed aerosol was quite unique at site B. However, mineral rock was remarkable at site A.     

Air quality measurements in urban green areas – a case study

The influence of traffic-induced pollutants (e.g. CO, NO, NO₂ and O₃) on the air quality of urban areas was investigated in the city of Essen, North Rhine-Westphalia (NRW), Germany. Twelve air hygiene profile measuring trips were made to analyse the trace gas distribution in the urban area with high spatial resolution and to compare the air hygiene situation of urban green areas with the overall situation of urban pollution. Seventeen measurements were made to determine the diurnal concentration courses within urban parks (summer conditions: 13 measurements, 530 30 min mean values, winter conditions: 4 measurements, 128 30 min mean values). The measurements were carried out during mainly calm wind and cloudless conditions between February 1995 and March 1996. It was possible to establish highly differentiated spatial concentration patterns within the urban area. These patterns were correlated with five general types of land use (motorway, main road, secondary road, residential area, green area) which were influenced to varying degrees by traffic emissions. Urban parks downwind from the main emission sources show the following typical temporal concentration courses: In summer rush-hour-dependent CO, NO and NO₂ maxima only occurred in the morning. A high NO₂/NO ratio was established during weather conditions with high global radiation intensities (K>800 W m⁻²), which may result in a high O₃ formation potential. Some of the values measured found in one of the parks investigated (Gruga Park, Essen, area: 0.7 km²), which were as high as 275 μg m⁻³ O₃ (30-min mean value) were significantly higher than the German air quality standard of 120 μg m⁻³ (30-min mean value, VDI Guideline 2310, 1996) which currently applies in Germany and about 20% above the maximum values measured on the same day by the network of the North Rhine–Westphalian State Environment Agency. In winter high CO and NO concentrations occur in the morning and during the afternoon rush-hour. The highest concentrations (CO=4.3 mg m⁻³, NO=368 μg m⁻³, 30-min mean values) coincide with the increase in the evening inversion. The maximum measured values for CO, NO and NO₂ do not, however, exceed the German air quality standards in winter and summer.     

Benzene,toluene, ozone,NO2 and SO2 measurements in an urban street canyon in Thessaloniki,Greece

Benzene, toluene, sulphur dioxide, ozone and nitrogen dioxide were measured at a mean level of 13.5 m above ground in a narrow, four-lane street canyon (height 30 m, width 20 m) in Thessaloniki, Greece during the period January–July 1997 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Primary pollutant levels were found to be 2.5–4.4 times higher during the cold part of the year than during the warm part of the year, the winter/summer ratio increasing with the reaction rate constant with OH for each of the measured species. Ozone, on the other hand, exhibited a winter/summer ratio of 0.36. NO₂ originates from both primary and secondary sources; its winter/summer concentration ratio of 1.4 lies, therefore, between those of primary pollutants and ozone. Pollution levels were influenced considerably by wind speed, while for the street canyon under study wind direction did not influence pollutant levels considerably. While primary pollution was found to decrease with increasing wind speed, ozone increased. Benzene mean levels during the study period were around 6 ppb and hence much higher than the EU annual limit value of 5 μg m⁻³ (1.44 ppb at STP). Toluene mean levels were around 14 ppb and hence also several times above the WHO recommendation of 2 ppb for 24 h. The apportionment of traffic emissions in four time zones used in most inventories in urban airshed models was tested using benzene and toluene measurements at low (<1 m s⁻¹) wind speeds. The agreement between model emissions and calculated emissions apportionment into the four time zones was good, except for Zone D (23:00–1:59), where model inventory emissions were somewhat too low.     

Carbonaceous and inorganic composition in long-range transported aerosols over northern Japan: Implication for aging of water-soluble organic fraction

To better understand the influence of sources and atmospheric processing on aerosol chemical composition, we collected atmospheric particles in Sapporo, northern Japan during spring and early summer 2005 under the air mass transport conditions from Siberia, China and surrounding seas. The aerosols were analyzed for inorganic ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and the major water-soluble organic compound classes (i.e., dicarboxylic acids and sugars). SO₄^2? is the most abundant inorganic constituent (average 44% of the identified inorganic ion mass) followed by NH₄⁺ (21%) and NO₃^? (13%). Concentrations of OC, EC, and WSOC ranged from 2.0–16, 0.24–2.9, and 0.80–7.9 μg m^?3 with a mean of 7.4, 1.0, and 3.1 μg m^?3, respectively. High OC/EC ratios (range: 3.6–19, mean: 8.7) were obtained, however WSOC/OC ratios (0.23–0.69, 0.44) do not show any significant diurnal changes. These results suggest that the Sapporo aerosols were already aged, but were not seriously affected by local photochemical processes. Identified water-soluble organic compounds (diacids + sugars) account for <10% of WSOC. Based on some marker species and air mass back trajectory analyses, and using stable carbon isotopic compositions of shorter-chain diacids (i.e., C₂–C₄) as photochemical aging factor of organic aerosols, the present study suggests that a fraction of WSOC in OC is most likely influenced by aerosol aging, although the OC loading in aerosols may be more influenced by their sources and source regions.     

Biases in Clean Air Status and Trends Network filter pack results associated with sampling protocol

Network filter pack sampling protocol changed in 1989 from requiring a week-long daytime sample and a week-long nighttime sample to requiring a single week-long sample per week at each monitoring site. In the current study, single-filter pack weekly results are compared with weekly results aggregated from separate daytime and nighttime weekly filter pack samples collected at the monitoring site located at Egbert, Ontario, Canada. Comparisons of the concentrations resulting from the two sampling protocols for all major chemical species (SO₄²⁻, NO₃⁻, NH₄⁺, HNO₃, and SO₂) show median biases of <5 nmol m⁻³ (0.1 ppb) and median relative biases of <10%. Median relative biases have the same sign for each species, suggesting biases in the same direction. Based on median differences, composite day–night weekly sampler results generally exceed the single-sampler weekly results (in all cases except for the summer nylon filter HNO₃), and the magnitude depends on the constituent and on the season. Examination of seasonal results reveals large discrepancies in some cases, especially during summer. To use Clean Air Status and Trends Network results for trends analyses over time periods encompassing the 1989 protocol change, it may be useful to put all of the data on the same basis of sampler protocol. Algorithms derived from linear regression analyses using paired bootstrap sampling are offered to convert the recent results to the pre-1989 basis; however, they may only be appropriate for sites in the eastern US. Chemical and statistical reasoning suggests that the results of day–night weekly sampling are usually consistent with higher accuracy than single-sampler weekly results. Adjustments are indicated for summer Teflon NO₃ and nylon HNO₃, for summer and fall Teflon NH₄, and for Total SO₂ in each season. Nylon filters are also shown to have variable collection characteristics for SO₂ that are consistent with a humidity effect. A network-wide change in the SO₂ collection and/or retention characteristics of the nylon filters is found in April 1997.     

Production and release of dimethylsulphide from an estuary in Portugal

The distribution of dimethylsuphide (DMS) and its precursor dimethylsulphoniopropionate, in both particulate (DMSP_p) and dissolved fractions (DMSP_d) was surveyed along estuarine water profiles of Canal de Mira (Ria de Aveiro, Portugal), on 45 occasions during one year. The field campaigns revealed pronounced gradients, which were to some extent interpreted with reference to supporting hydrographic parameters like salinity, temperature and chlorophyll a. Surface water concentrations showed a clear seasonal variation with peak values during the warmer months. Mean summer concentrations for DMS, DMSP_p and DMSP_d, were, respectively, a factor of 1.8, 1.9 and 2.9 times higher than winter concentrations. Surface water concentration was the main factor controlling DMS emissions into the atmosphere, which were estimated to be, as a mean, 5.4 and 27.3 nmol m^-2 h^-1 for winter and summer, respectively. In addition, DMS fluxes from two intertidal mud flat sites in Canal de Mira were examined monthly over a year. Average emission rates were a factor of 2–5 times higher than those estimated for estuarine waters and revealed strong seasonal variations, with summer peaks apparently related to ambient temperature. The relative contribution of estuarine waters and mud flats for local DMS budget is discussed in terms of tidal cycles and exposed surface area.