Ten years measuring PCDDs/PCDFs in ambient air in Catalonia (Spain)

This work summarizes the results of a ten year surveillance programme on PCDD/F in ambient air carried out in Catalonia (Spain). The study has been conducted by the Dioxin Laboratory of Spanish Council for Scientific Research (CSIC) in collaboration with the Environment Department of the Catalonian Government. 175 samples have been collected throughout Catalonia from 1994 to 2004. Different sampling locations classified as industrial, traffic, urban, suburban and rural sites have been monitored in order to find the most contaminated zones as well as the ones with expected background concentrations. The highest concentrations found in this study were determined at the industrial locations. Concentrations ranging from 5 to 1196 fg I-TEQ/m3, with a mean value of 140 fg I-TEQ/m3 and from 10 to 357 fg I-TEQ/m3, with a mean value of 72 fg I-TEQ/m3 were determined in industrial and traffic sampling points, respectively. In contrast, the lowest concentrations were found in rural stations, ranging from 5 to 45 fg I-TEQ/m3, with a mean value of 28 fg I-TEQ/m3. The PCDD/F concentration trend in Catalonian ambient air shown a clear drop of the median values occurred during the study sampling period. A decline of about 70% was observed from 1997-1998 to 2003-2004.     

Air and soil dioxin levels at three sites in Italy in proximity to MSW incineration plants

Levels of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in both air and soil samples were measured at three different sites in Italy, in proximity to three municipal solid waste incinerators (MSWIs) to determine baseline contamination and the contributory role of incinerator emissions. At the first site, located in an agricultural, cattle-breeding, typically flattish area of the Po Valley, the dioxin concentrations had already been measured before the start-up of the new MSWI. These dioxin concentrations were then again measured after two years of continual operation of the incinerator. Despite the presence of the plant, the PCDD/Fs concentrations appear not to have been affected and were found to be in a range of 22-125 fg I-TEQ m(-3) in the air samples and 0.7-1.5 pg I-TEQ g(-1) in the soil samples. The second site is located in an industrial district of the Veneto Region, in the surroundings of an old MSWI that is not equipped with Best Available Technology (BAT) dioxin removal system. The PCDD/Fs concentrations in the air samples were between 144 and 337 fg I-TEQ m(-3). This is a typical range of values for industrial areas, while the soil samples showed contamination levels between 1.1 and 1.4 pg I-TEQ g(-1). The third site lies in the Adige Valley, near a MSWI that has been equipped with BAT for flue gas cleaning. The observed values ranged from 10 to 67 fg I-TEQ m(-3) for the air samples and 0.08-1.2 pg I-TEQ g(-1) for the soil samples. The contributory factors of the varying characteristics of the different areas together with the types of technology adopted at each MSWI plant are discussed. The PCDD/Fs levels are subsequently compared with established values from previous studies.     

The PCDD/F and PBDD/F pollution in the ambient atmosphere of Shanghai, China

Rapid economic growth in the last two decades in Shanghai has had a great adverse influence on its air quality. Therefore, the atmospheric pollutants of Shanghai have received much concern. In this study, concentrations of 2,3,7,8-substituted PCDD/Fs and PBDD/Fs congeners were measured in the ambient air of four districts in Shanghai. The mean atmospheric concentrations (TEQs) of total 2,3,7,8-PCDD/Fs and 2,3,7,8-PBDD/Fs were 8031 fg m(-3) (497.1 fg I-TEQ m(-3)) and 1358 fg m(-3) (304.1 fg I-TEQ m(-3)) for Jiading District, 5308 fg m(-3) (289.0 fg I-TEQ m(-3)) and 709 fg m(-3) (146.9 fg I-TEQ m(-3)) for Zhabei District, 4014 fg m(-3) (144.4 fg I-TEQ m(-3)) and 1239 fg m(-3) (256.9 fg I-TEQ m(-3)) for Pudong District, 3348 fg m(-3) (143.2 fg I-TEQ m(-3)) and 699 fg m(-3) (148.4 fg I-TEQ m(-3)) for Huangpu District, respectively. Our results showed that almost all the PCDD/Fs and PBDD/Fs congeners were partitioned into the particulate phase except the lower chlorinated or brominated ones. The logarithm of the gas/particle partitioning coefficient K(p) has good linear correlation with that of the sub-cooled vapor pressure p(L). Concentrations of PCDD/Fs and PBDD/Fs were both positively correlated to elemental carbon in all districts except Pudong District, suggesting elemental carbon could be a good indicator for dioxins' air pollution. It is intensively suggested that more detailed and deeper studies about PBDD/Fs should be carried out due to their relatively high atmospheric concentrations in Shanghai.     

Evaluation of PCDD/F levels in ambient air and soils and estimation of deposition rates in Kocaeli, Turkey

PCDD/F analyses were made in soil and ambient air samples taken from Kocaeli, an industrialized area of Turkey. Results showed that the levels of PCDD/F pollution are comparable to the levels observed in the various urban areas in the world. PCDD/F concentrations in surface soils ranged between 0.4 and 4.27 pg I-TEQ kg(-1) with a geometric mean of 0.76 pg I-TEQ kg(-1), while those in ambient air were between 23 and 563 f gm(-3), with geometric mean of 82.0 f gm(-3). Ambient air PCDD/F concentration in the city center was about 10 times higher than those in the rural area. Combustion activities present in the area were assessed to be the most significant source of the PCDD/F pollution based on the congener and homologue profiles and statistical analysis of the data. The deposition rate modeling of USEPA was applied and the deposition rates were determined in the range between 7.6 and 66.3 ng I-TEQ m(-2)year(-1) with a geometric mean of 15.9 ng I-TEQ m(-2)year(-1). The rates were higher than the recommended deposition rates in relation to the tolerable daily intake (TDI) range of PCDD/Fs for humans. The deposition velocities computed were also found to be high in both low and highly chlorinated PCDD/Fs, and this was attributed to the vapor phase deposition of volatile PCDD/Fs, and the scavenging effect of the precipitation on the particle-bound PCDD/Fs.     

Statistical investigation of polychlorinated dibenzo-p-dioxins and dibenzofurans in the ambient air of Houston, Texas

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (dioxins and furans) are persistent, bioaccumulative and highly toxic chemical constituents that appear in the environment at very low and difficult to measure levels. Although dioxins and furans are widely recognized as toxic contaminants needing regulation, their temporal and spatial concentration profiles and the factors impacting their partitioning and congener distribution are only moderately understood. This paper presents the results from one of the most extensive ambient air dioxin and furan sampling efforts conducted in a geographic area to date. The data consist of monthly ambient concentrations of 17 of the most toxic congeners of dioxins and furans collected at five locations in Houston, Texas over a calendar year. The results showed a total annual mean dioxin and furan congener concentration of 1047 fg/m3 and an annual mean summation operatorI-TEQ concentration of 15 fg I-TEQ/m3 (16 fg WHO-TEQ/m3). These results, when compared with proximate data from the USEPA National Dioxin Ambient Monitoring Network (NDAMN), revealed significant (at the P0.05 level) differences between Houston and the NDAMN sites, suggesting the existence of local dioxin sources. A temporal analysis of the data showed that the congener concentration distribution varies over time, depending on the level of chlorination, type of congener, and temperature. The results also suggested that the fluctuations of congener concentrations and I-TEQ concentrations are closely correlated with minimum relative humidity, mean temperature, and mean NOx concentration.     

C1–C8 volatile organic compounds in the atmosphere of Hong Kong: Overview of atmospheric processing and source apportionment

We present measurements of C₁–C₈ volatile organic compounds (VOCs) at four sites ranging from urban to rural areas in Hong Kong from September 2002 to August 2003. A total of 248 ambient VOC samples were collected. As expected, the urban and sub-urban sites generally gave relatively high VOC levels. In contrast, the average VOC levels were the lowest in the rural area. In general, higher mixing ratios were observed during winter/spring and lower levels during summer/fall because of seasonal variations of meteorological conditions. A variation of the air mass composition from urban to rural sites was observed. High ratios of ethyne/CO (5.6 pptv/ppbv) and propane/ethane (0.50 pptv/pptv) at the rural site suggested that the air masses over the territory were relatively fresh as compared to other remote regions. The principal component analysis (PCA) with absolute principal component scores (APCS) technique was applied to the VOC data in order to identify and quantify pollution sources at different sites. These results indicated that vehicular emissions made a significant contribution to ambient non-methane VOCs (NMVOCs) levels in urban areas (65±36%) and in sub-urban areas (50±28% and 53±41%). Other sources such as petrol evaporation, industrial emissions and solvent usage also played important roles in the VOC emissions. At the rural site, almost half of the measured total NMVOCs were due to combustion sources (vehicular and/or biomass/biofuel burning). Petrol evaporation, solvent usage, industrial and biogenic emissions also contributed to the atmospheric NMVOCs. The source apportionment results revealed a strong impact of anthropogenic VOCs to the atmosphere of Hong Kong in both urban/sub-urban and rural areas.     

Long-term monitoring and modeling of polychlorinated dibenzo-p-dioxins and dibenzofurans from municipal solid waste incinerators and surrounding area in northern Taiwan

Municipal solid waste incinerators (MSWIs) have long been the major contributors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) to ambient air in Taiwan. After stringent MSWI emission standards were introduced in 2001, the long-term continuous monitoring of flue gas and ambient air quality became necessary to ensure the effectiveness of the related control strategies. Three MSWIs and the surrounding ambient air were investigated in the current study for PCDD/F characteristics during 2006 to 2011. The average concentrations in the flue gas ranged from 0.008?~?0.0488 ng I-TEQ/Nm³, which is much less than the emission standard in Taiwan (0.1 ng I-TEQ/Nm³) (I-TEQ is the abbreviation of International Toxic Equivalent). This led to extremely low levels in the ambient air, 0.0255 pg I-TEQ/Nm³, much less than the levels seen in most urban areas around the world. Additionally, the results obtained using the Industrial Source Complex Short-Term Dispersion Model (ISCST3) indicate that the PCDD/F contributions from the three MSWIs to the ambient air were only in the range from 0.164?~?0.723 %. Principal component analysis (PCA) showed that the PCDD/Fs in the air samples had very similar characteristics to those from mobile sources. The results thus show that stringent regulations have been an effective control strategy, especially for urban areas, such as Taipei City.     

A study of polychlorinated dibenzo-p-dioxins and dibenzofurans in the atmosphere of Hong Kong

A total of 27 ambient air samples of were collected from six locations in Hong kong during the period of January-August, 2000 and analysed for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In all sampling locations, higher concentrations of PCDDs/PCDFs, ranging from 0.03 to 0.43 pg I-TEQ/m3 were measured in winter months (January and March) than in the summer months (July and August) of concentrations at 0.018-0.025 pg I-TEQ/m3. These concentrations are similar to annual ranges reported earlier for two Hong Kong urban sites and other urban cities in Asia. Europe, and the United States. Despite significant seasonal variations in ambient air concentrations of PCDD/Fs (expressed in I-TEQ) were observed, the congener profiles of all the samples in this study period were similar, with OCDD, 1,2,3,4,6,7,8-HpCDD, OCDF and 1,2,3,4,6,7,8-HpCDF being the predominant species. However, the homologue profiles for the samples collected at the six locations of this study were found to display significantly different spatial and seasonal trends.     

Atmospheric mercury monitoring survey in Beijing,China

With the aid of one industrial, two urban, two suburban, and two rural sampling locations, diurnal patterns of total gaseous mercury (TGM) were monitored in January, February and September of 1998 in Beijing, China. Monitoring was conducted in six (two urban, two suburban, one rural and the industrial sites) of the seven sampling sites during January and February (winter) and in four (two urban, one rural, and the industrial sites) of the sampling locations during September (summer) of 1998. In the three suburban sampling stations, mean TGM concentrations during the winter sampling period were 8.6, 10.7, and 6.2 ng/m3, respectively. In the two urban sampling locations mean TGM concentrations during winter and summer sampling periods were 24.7, 8.3, 10, and 12.7 ng/m3, respectively. In the suburban-industrial and the two rural sampling locations, mean mercury concentrations ranged from 3.1-5.3 ng/m3 in winter to 4.1-7.7 ng/m3 in summer sampling periods. In the Tiananmen Square (urban), and Shijingshan (suburban) sampling locations the mean TGM concentrations during the summer sampling period were higher than winter concentrations, which may have been caused by evaporation of soil-bound mercury in warm periods. Continuous meteorological data were available at one of the suburban sites, which allowed the observation of mercury concentration variations associated with some weather parameters. It was found that there was a moderate negative correlation between the wind speed and the TGM concentration at this suburban sampling location. It was also found that during the sampling period at the same site, the quantity of TGM transported to or from the sampling site was mainly influenced by the duration and frequency of wind occurrence from certain directions.     

Multivariant statistical analysis of PCDD/FS in sewage sludges from different areas of the Valencian Community (Spain)

The levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in 31 sewage sludges from different wastewater treatment plants corresponding to rural, urban and industrial areas in the Valencian Community (Spain) were analysed. Values of 5.1-346.2 ng I-TEQ kg(-1) (dry weight) were detected for sewage sludge with the highest value in one sample from an industrial area. Therefore the majority of the samples did not exceed the limit proposed (100 ng I-TEQ kg(-1)) by the [EU, 2000. Working document on sludge, 3rd draft. Brussels. Available from: http://europa.eu.int/comm/environment/waste/sludge/sludge_en.pdf] for use in agriculture. The dominant congeners for each family of compounds were 1,2,3,4,6,7,8-HpCDD and OCDD from PCDDs, and 1,2,3,4,6,7,8-HpCDF and OCDF from PCDFs. The total concentrations of PCDD/Fs were evaluated statistically through SPPS 11.0 for Windows. The principal component analysis (PCA) was used to extract two PCs as a linear combination of the original variables, one of them associated to urban+highly industrial areas and the other one to urban+low industrial areas. The linear regression method was applied and an efficient correlation was obtained between the total I-TEQ values for each sample and two of most abundant congeners (OCDF and OCDD). This expression was obtained with the results of the 31 samples analysed and a variety of data from other authors. Furthermore, several bilateral correlations between the different congeners completed the statistical analysis.     

Characteristics and diurnal variations of NMHCs at urban,suburban, and rural sites in the Pearl River Delta and a remote site in South China

The Pearl River Delta (PRD) is one of the most industrialized and urbanized regions in China. With rapid growth of the economy, it is suffering from deteriorating air quality. Non-methane hydrocarbons (NMHCs) were investigated at urban and suburban sites in Guangzhou (GZ), a rural site in PRD and a clean remote site in South China, in April 2005. Additional roadside samples in GZ and Qingxi (QX, a small industrial town in PRD), ambient air samples at the rooftop of a printing factory in QX and exhaust samples from liquefied petroleum gas (LPG)—fueled taxis in GZ were collected to help identify the source signatures of NMHCs. A large fraction of propane (47%) was found in exhaust samples from LPG-fueled taxis in GZ and extremely high levels of toluene (2.0–3.1 ppmv) were found at the rooftop of the printing factory in QX. Vehicular and industrial emissions were the main sources of NMHCs. The effect of vehicular emission on the ambient air varied among the three PRD sites. The impact of industrial emissions was widespread and they contributed greatly to the high levels of aromatic hydrocarbons, especially toluene, at the three PRD sites investigated. Leakage from vehicles fueled by LPG contributed mainly to the high levels of propane and n-butane at the urban GZ site. Ethane and ethyne from long-range transport and isoprene from local biogenic emission were the main contributors to the total hydrocarbons at the remote site. Diurnal variations of NMHCs showed that the contribution from vehicular emissions varied with traffic conditions and were more influenced by fresh emissions at the urban site and by aged air at the suburban and rural sites. Isoprene from biogenic emission contributed largely to the ozone formation potential (OFP) at the remote site. Ethene, toluene and m/p-xylene were the main contributors to the OFP at the three PRD sites.     

Urban-Center CO Air Quality Projections

The distribution of mutagenic activity and nitroaromatic components of polycyclic organic matter (POM) in ambient air at industrial, urban, suburban, rural, and remote sites was studied using organic extracts from high volume aerosol samples. Direct-acting mutagens including 1-nitropyrene (1-NP), dinitropyrenes (DNP), and hydroxynitropyrenes (HNP) were measured by high performance liquid chromatography while the mutagenicity was determined in the Salmonella bioassay with strain TA-98. Benzo(a)pyrene (BaP), one of the possible precursors of nitroaromatic compounds in POM, was also measured. In comparing samples from a range of sites, TSP and the concentration of BaP per mass of particulate matter decreased, as expected, at greater distances from urban and industrial combustion sources. However, the concentrations of polar nitroaromatic POM compounds per mass of particles were higher at a remote site than in nonindustrial urban and suburban areas. The mutagenicity in particulate matter extracts from the remote area was predominantly (>90 percent) in the very polar fractions. There were also high atmospheric levels of nitroaromatic compounds and mutagenicity in heavily industrialized areas. These observations may reflect the influences of source emissions, atmospheric transformations of POM compounds, and ther atmospheric processes on the composition of ambient suspended particulate matter.     

Seasonal variation of PCDD/Fs in the metropolis of Istanbul,Turkey

Atmospheric concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) compounds were investigated at three different regions of Istanbul which reflect urban, urban/industrial, and sub-urban characteristics. Air samples were collected simultaneously for both gaseous and particulate phases using high volume samplers on monthly time intervals from May 2011 to October 2012. The highest concentrations (3,056 fg/m³ and 156 fg I-TEQ/m³) were observed at the sampling site that reflects traffic, residential, and industrial emission source characteristics, while the lowest concentrations (829 fg/m³ and 38 fg I-TEQ/m³) were observed at the sampling point which is far away from centrum and reflects sub-urban characteristics. Concentrations of PCDD congeners were, in general, found to be higher than PCDF congeners, and OCDD, 1,2,3,4,6,7,8-HpCDD/F, and OCDF congeners were recorded to be the most abundant congeners. Winter season concentrations were also found to be higher especially in particulate phase. As a result, combustion processes such as motor vehicles and residential heating equipment were thought to be the principal sources of emissions of PCDD/F compounds when both congener profiles and seasonal variations are considered. Basic statistical evaluation of the data resembled high degree of inverse correlations between PCDD/F concentrations and UV and solar radiation.     

Atmospheric deposition of PCDD/Fs near an old municipal solid waste incinerator: levels in soil and vegetation

The levels of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were determined in soil and vegetation samples taken from 24 sites in the vicinity of an old municipal solid waste incinerator (San Adrià del Besòs, Barcelona, Spain). Duplicate samples were collected within a radius of 3 km from the stack. PCDD/F concentrations in soils ranged from 1.22 to 34.28 ng I-TEQ/kg (d.m.) with median and mean values of 9.06 and 12.24 ng I-TEQ/kg, respectively. In turn, the levels of PCDD/Fs in vegetation samples ranged from 0.33 to 1.98 ng I-TEQ/kg (d.m.), with median and mean values of 0.58 and 0.70 ng I-TEQ/kg, respectively. Although the present PCDD/F concentrations in soil samples were higher than those recently found in soils taken near other incinerators from Catalonia, they are of the same order of magnitude than the levels of these pollutants found in incinerators from other countries. By contrast, the concentrations of PCDD/Fs in herbage samples were comparable to those found in recent surveys carried out in Catalonia.     

Ground-level ozone in the Pearl River Delta region: Analysis of data from a recently established regional air quality monitoring network

The ambient air quality monitoring data of 2006 and 2007 from a recently established Pearl River Delta (PRD) regional air quality monitoring network are analyzed to investigate the characteristics of ground-level ozone in the region. Four sites covering urban, suburban, rural and coastal areas are selected as representatives for detailed analysis in this paper. The results show that there are distinct seasonal and diurnal cycles in ground-level ozone across the PRD region. Low ozone concentrations are generally observed in summer, while high O₃ levels are typically found in autumn. The O₃ diurnal variations in the urban areas are larger than those at the rural sites. The O₃ concentrations showed no statistically significant difference between weekend and weekdays in contrast to the findings in many other urban areas in the world. The average ozone concentrations are lower in urban areas compared to the sites outside urban centers. Back trajectories are used to show the major air-mass transport patterns and to examine the changes in ozone from the respective upwind sites to a site in the center of the PRD (Wanqingsha). The results show higher average ozone concentrations at the upwind sites in the continental and coastal air masses, but higher 1 h-max O₃ concentrations (by 8–16 ppbv) at the center PRD site under each of air-mass category, suggesting that the ozone pollution in the PRD region exhibits both regional and super-regional characteristics.     

Influence of a municipal solid waste incinerator on ambient air and soil PCDD/Fs levels

To examine the influence of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) emissions from a municipal solid waste incinerator (MSWI) on the environment, we measured the levels of PCDD/Fs in ambient air and soil samples collected near a MSWI in Bucheon, Korea. The PCDD/Fs concentrations in the ambient air samples ranged from 0.22 to 1.16 pg I-TEQm(-3) (13.39-75.16 pg m(-3)), with an average of 0.66 pg I-TEQ m(-3) (35.62 pg m(-3)). The soil samples contained between 1.25 and 74.98 pg I-TEQ g(-1) (38.15-3,303.33 pg g(-1)), with an average of 19.06 pg I-TEQ g(-1) (1,077.11 pg g(-1)). These levels were higher than those previously reported by other investigators in a number of surveys. The furan homologues predominated in the air samples and some soil samples, and the soil PCDD/Fs levels decreased with increasing distance from the MSWI. Comparison of the homologue patterns and a multivariate statistical analysis showed that PCDD/Fs emission from the MSWI directly affected the pattern of PCDD/Fs in air, while the PCDD/Fs patterns in soil differed according to the location relative to the MSWI, roads, and construction sites. These results collectively indicate that the MSWI was the major PCDD/Fs emission source in this area, but that unidentified combustion sources and vehicles might influence the environment to some extent.     

PCDD/F concentrations in milk of nonoccupationally exposed women living in southern Catalonia, Spain

Concentrations of 17 toxic 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) have been determined in pooled samples of breast milk from 15 mothers living in two residential areas (Tarragona downtown and an industrial area) in the vicinity of a new hazardous waste incinerator (HWI), now under construction in Tarragona (southern Catalonia, Spain). PCDD/Fs in human milk samples ranged between 5.9 and 17.1 pg I-TEQ/g fat (162-498 pg I-TEQ/l), with a mean value of 11.8 pg I-TEQ/g fat (310.8 pg I-TEQ/l). The percentages of fat ranged between 1.53 and 3.52. Although PCDD/F levels in milk from mothers living in the industrial area were found to be slightly higher than those observed in women living Tarragona downtown, most differences did not reach the level of statistical significance. In general terms, PCDD/F concentrations in human milk (pooled) samples of mothers living in the area of Tarragona are similar or lower than those previously reported for most industrialized countries.     

Atmospheric mercury levels in the Slovak Republic.

Total mercury concentrations (as a sum of vapor and particulate mercury) were measured in 24-h samples of ambient air in 20 different localities of the Slovak Republic eight times during the period 1996-1997. Vapor mercury was analyzed on site by atomic fluorescence with amalgamation technique. Particulate mercury was determined by vapor hydride atomic absorption spectrometry after wet digestion of filters with particulate air samples. The results showed that 34% of the 160 individual total mercury concentrations exceeded 5 ng/m3--the ambient air quality guideline value recommended by the WHO. The range of total mercury concentrations in the ambient air of Slovakia was: 1.13-3.98 ng/m3 (geom. mean 2.63) in the background area; 2.25-5.27 ng/m3 (geom. mean 3.64) in the agricultural areas; 1.73-20.53 ng/m3 (geom. mean 4.57) in the urban areas; and 1.53-39.85 ng/m3 (geom. mean 5.28) in the industrial areas. The highest mercury levels occurred in areas with metallurgical industry and coal combustion. The predominant form of mercury present in air was vapor mercury. The particulate fraction of mercury in ambient air (as a percentage of total mercury) varied widely from 0.4% to 42.1% (geom. mean = 4.4%). This fraction was lower in agricultural areas (2.3%) than in urban areas (5.3%). Although the atmospheric vapor mercury concentrations were slightly higher in summer than in winter, a direct correlation of vapor mercury concentrations and ambient air temperature was not found. Furthermore, the particulate mercury concentrations did not correlate with total particulate levels.     

On the local and regional influence on ground-level ozone concentrations in Hong Kong

Hong Kong is a densely populated city situated in the fast developing Pearl River Delta of southern China. In this study, the recent data on ozone (O3) and related air pollutants obtained at three sites in Hong Kong are analyzed to show the variations of O3 in urban, sub-urban and rural areas and the possible regional influences. Highest monthly averaged O3 was found at a northeastern rural site and lowest O3 level was observed at an urban site. The levels of NOx, CO, SO2 and PM10 showed a different spatial pattern with the highest level in the urban site and lowest at the rural site. Analysis of chemical species ratios such as SO2/NOx and CO/NOx indicated that the sites were under the influences of local and regional emissions to varying extents reflecting the characteristics of emission sources surround the respective sites. Seasonal pattern of O3 is examined. Low O3 level was found in summer and elevated levels occurred in autumn and spring. The latter appears different from the previous result obtained in 1996 indicating a single maximum occurring in autumn. Principal component analysis was used to further elucidate the relationships of air pollutants at each site. As expected, the O3 variation in the northeastern rural area was largely determined by regional chemical and transport processes, while the O3 variability at the southwestern suburban and urban sites were more influenced by local emissions. Despite the large difference in O3 levels across the sites, total potential ozone (O3+NO2) showed little variability. Cases of high O3 episodes were presented and elevated O3 levels were formed under the influence of tropical cyclone bringing in conditions of intense sunlight, high temperature and light winds. Elevated O3 levels were also found to correlate with enhanced ratio of SO2 to NOx, suggesting influence of regional emissions from the adjacent Pearl River Delta region.     

Elevated atmospheric CO2 concentration and temperature across an urban–rural transect

The heat island effect and the high use of fossil fuels in large city centers are well documented, but by how much fossil fuel consumption is elevating atmospheric CO₂ concentrations and whether elevations in both atmospheric CO₂ and air temperature from rural to urban areas are consistently different from year to year are less well known. Our aim was to record atmospheric CO₂ concentrations, air temperature and other environmental variables in an urban area and compare it to suburban and rural sites to see if urban sites are experiencing climates expected globally in the future with climate change. A transect was established from Baltimore city center (Urban site), to the outer suburbs of Baltimore (suburban site) and out to an organic farm (rural site). At each site a weather station was set-up to monitor environmental variables for 5 years. Atmospheric CO₂ was consistently and significantly increased on average by 66 ppm from the rural to the urban site over the 5 years of the study. Air temperature was also consistently and significantly higher at the urban site (14.8 °C) compared to the suburban (13.6 °C) and rural (12.7 °C) sites. Relative humidity was not different between sites whereas the vapor pressure deficit (VPD) was significantly higher at the urban site compared to the suburban and rural sites. An increase in nitrogen deposition at the rural site of 0.6% and 1.0% compared to the suburban and urban sites was small enough not to affect soil nitrogen content. Dense urban areas with large populations and high vehicular traffic have significantly different microclimates compared to outlying suburban and rural areas. The increases in atmospheric CO₂ and air temperature are similar to changes predicted in the short term with global climate change, therefore providing an environment suitable for studying future effects of climate change on terrestrial ecosystems.