What factors drive copepod community distribution in the Gulf of Gabes,Eastern Mediterranean Sea?

The spatial and temporal variations in copepod communities were investigated during four oceanographic cruises conducted between July 2005 and March 2007 aboard the R/V Hannibal. A close relationship was observed between the temperature, salinity, hydrographic properties and water masses characterising the Gulf of Gabes. Indeed, water thermal stratification began in May–June, and a thermocline was established at a 20-m depth, but ranged from 25 m in July to more than 30 m in September. The zooplankton community is dominated by copepods representing 69 % to 83 % of total zooplankton. Spatial and temporal variation of copepods in relation to environmental factors shows their close relationship with the hydrodynamic features of the water column. Thermal stratification in the column, established in summer, supports copepod development. In fact, copepod abundance increases gradually with rising water temperature and salinity, starting from the beginning of thermal stratification (May–June 2006) and lasting until its completion (July 2005 and September 2006). When the water column is well mixed (March 2007), copepod abundance decreased. Our finding shows that temperature and salinity seem to be the most important physical factors and thus strongly influence the taxonomic diversity and distribution of the copepod population. They are characterised by the dominance of Oithona nana, representing 75–86 % of total cyclopoid abundance. The most abundant species during the stratification period were O. nana, Acartia clausi and Stephos marsalensis in July 2005 and September 2006. However, during the mixing period, Euterpina acutifrons was more abundant, representing 21 % of the total. Unlike the copepod community, which is more abundant during the period of high stratification, phytoplankton proliferates during semi-mixed conditions.     

Ultraviolet radiation spatio-temporal characteristics derived from the ground-based measurements taken in China

Ultraviolet (UV) radiation and broadband solar radiation (R_s) measured from January 2005 to June 2006 at 31 stations in Chinese Ecosystem Research Network (CERN) were used to investigate the spatio-temporal characteristics of UV radiation and UV fraction (the ratio of UV radiation to R_s) in China. Results indicated that the seasonal variations of UV radiation and R_s were consistent with the solar activities, which reached their lower values during winter period, and increased throughout the spring, peaking in June or July, in most sites. The Meiyu weather system and Southwest Monsoon produced different variation characteristics of UV radiation and R_s in subtropical and tropical regions. The UV fraction values showed a similar seasonal trend as that of UV radiation, which was mainly determined by the seasonal change of the aerosol optical depth (AOD) and water vapor content in atmosphere. The seasonal variations of UV fraction were much smoother in southern China due to high water vapor content over the whole year.The UV radiation showed an increasing trend from east to west in China. In the western area, a simple increasing trend was observed from north to south, with the largest annual mean daily UV value 0.91 MJ m⁻² appearing in the Qinghai-Tibet Plateau area. In east China there was a low center that appeared in the subtropical region due to high aerosol burden, with the lowest value 0.41 MJ m⁻² observed in Yanting site. Two high centers were located in the tropics with higher solar altitudes and the north desert region with low atmospheric attenuation. The largest values of UV fraction appeared in the tropical and subtropical regions due to higher relative humidity (RH) in these areas. However, the smallest value did not appear in the north desert region where the RH was the lowest, they were found at the Luancheng site which featured relatively low humidity and abundant fine aerosols. The variations in the UV fraction were not such distinctive as those of the UV radiation in China due to the more complex influences of aerosol and water vapor.     

Isoprene and its degradation products as strong ozone precursors in Insubria,Northern Italy

Frequent smog episodes occur during spring, summer, and autumn in Insubria, Northern Italy. On a test site in this area the atmospheric concentration of the photo-oxidants ozone and peroxyacetyl nitrate has been monitored over a year (2000) together with ozone precursors listed in the European Union Air Quality Directive 2002/3/EC, such as nitrous oxides (NO_X) and volatile organic compounds (VOC) including hydrocarbons and carbonyls. The results of this study revealed a strong impact of biogenic isoprene on the air quality.In winter isoprene was detected at the ppt level and correlated with anthropogenic VOC. However, during the growing season isoprene exhibited a distinct diurnal variation with maximum concentrations late in the afternoon reaching up 70 ppbC attributed to strong emissions from the abundant vegetation of broad-leaf deciduous trees in this area. A new HPLC-MS method was developed for the determination of isoprene's primary atmospheric oxidation products methacrolein as its 2,4-dinitrophenylhydrazone and methyl vinyl ketone as an unusual double derivative with 2,4-dinitrophenylhydrazine. Methacrolein and methyl vinyl ketone followed the same diurnal and annual trends as isoprene. The average monthly concentration of isoprene and these products ranged from around 10 ppbC in June, July and September to 20 ppbC in August, which constitutes 15–30% of C₃–C₉ VOCs. The contribution from isoprene photo-oxidation to the ambient air formaldehyde concentrations was also found to be high during this period ranging from 30% to 60% in May, June, July and August.From the atmospheric VOC and NO_X concentrations the local photochemical ozone formation was estimated by the incremental reactivity approach. The calculations showed that in summer isoprene's contribution to the local ozone formation was as high as 50–75%.     

Effect of fireworks on ambient air quality in Malta

Religious festivals (festas) in the densely populated Maltese archipelago (Central Mediterranean) are ubiquitous during summer when 86 of them are celebrated between June and October, each involving the burning of fireworks both in ground and aerial displays over a period of 3 days or longer per festival. We assessed the effect of fireworks on the air quality by comparing PM₁₀ and its content of Al, Ba, Cu, Sr and Sb which materials are used in pyrotechnic compositions. PM₁₀ was collected mainly from two sites, one in Malta (an urban background site) and the other in Gozo (a rural site) during July–August 2005 when 59 feasts were celebrated and September–October 2005 when only 11 feasts occurred. For both Malta and Gozo, PM₁₀ and metal concentration levels measured as weekly means were significantly higher during July–August compared to September–October and there exist strong correlations between PM₁₀ and total metal content. Additionally, for Malta dust, Al, Ba, Cu and Sr correlated strongly with each other and also with total concentration of all five metals. The same parameters measured in April 2006 in Malta were at levels similar to those found in the previous October. Ba and Sb in dust from the urban background site in Malta during July–August were at comparable or higher concentration than recently reported values in PM₁₀ from a heavily-trafficked London road and this suggests that these metals are locally not dominated by sources from roadside materials such as break liner wear but more likely by particulate waste from fireworks. Our findings point to the fact that festa firework displays contribute significantly and for a prolonged period every year to airborne dust in Malta where PM₁₀ is an intractable air quality concern. The presence in this dust of elevated levels of Ba and especially Sb, a possible carcinogen, is of concern to health.     

Ozone and UV-B variations at Ispra from 1993 to 1997

An analysis of the variability of the total ozone column at Ispra (Italy) has been performed to ascertain if, even in a short-time interval of 5 years (1993–1997), a decline of the monthly mean ozone values could be demonstrated. A linear fit of the data displays a decrease of 0.21% per year with a mean value equal to 319±2 D.U. and an amplitude of the annual cycle of about 10% of the mean. A linear regression of the surface monthly mean ozone values has also been performed showing a decreasing trend (−1% per year) that could contribute, even if for a very small amount, to the decline of the total ozone values. Ispra monthly mean total ozone data have been compared with those of three stations located within 2° latitude and 3° longitude from Ispra (Haute Provence, Hohenpeissenberg and Arosa). A linear fit of the data shows some discrepancies in the ozone changes, which can be attributed to the limited length of the observational period.An analysis has been performed to verify if the variation of ozone at Ispra is in agreement with that of the solar UV measured at a wavelength (305 nm) where the ozone absorption is still remarkable. The results, taken at a fixed solar zenith angle of 68°, show a clear anticorrelation between the monthly mean values of UV and the corresponding values of the total ozone column; the linear fit of the UV data displays an increase of 2.0% per year, much higher than expected from the ozone decrease, and a mean value of 1.4±0.1 mW m^-2 nm^-1.     

Atmospheric characteristics conducive to high-ozone days in the Atlanta metropolitan area

The purpose of this paper is to identify the atmospheric conditions associated with elevated ground-level ozone concentrations during June–August of 2000–2007 at 11 ozone-monitoring stations in the Atlanta, GA, USA metropolitan statistical area (MSA). Analyses were confined to high-ozone days (HODs), which had a daily maximum 8-h average ozone concentration in the 95th percentile of all June–August values. Therefore, each station had 36 HODs. The southeastern and far northern portions of the MSA had HODs with the highest and lowest ozone concentrations, respectively. HODs at nearly all Atlanta MSA ozone-monitoring stations were enabled by migratory anticyclones. HODs for most stations were hot, dry, and calm with low morning mixing heights and high afternoon mixing heights. All sets of HODs had daily mean relative humidities and afternoon mixing heights that, respectively, were significantly less than and significantly greater than mean values for the remaining days. Urbanized Atlanta typically was upwind of an ozone-monitoring station on its HODs; therefore, wind direction on HODs varied considerably among the stations. HODs may have been caused partially by NO_x emissions from electric-utility power plants: HODs in the southern portion of the MSA were linked to air-parcel trajectories intersecting a power plant slightly northwest of Atlanta and plants in the Ohio River Valley, while HODs in the northern portion of the MSA were linked to air-parcel trajectories intersecting two large power plants slightly southeast of the Atlanta MSA. Results from this study suggest that future research in the Atlanta MSA should focus on power-plant contributions to ground-level ozone concentrations as well as the identification of non-monitored locations with potentially high ozone concentrations.     

Observational study of ozone pollution at a rural site in the Yangtze Delta of China

Ozone and related trace gases (CO, NO_x, and SO₂) were measured from June 1999 to July 2000 at a rural site in the Yangtze Delta of China, a region of intensive anthropogenic activity. Elevated ozone levels were frequently observed during the study period, with the highest frequency in late spring and early summer. Over a 1 yr period, 21 d were found to have ozone concentrations exceeding the new US 8-h 80 ppb health standard. Calculation of the “SUM06” exposure index also shows relatively high (>15 ppm h) values for each season except winter. At these levels ozone may have adverse effects on human health as well as agricultural crops. Analysis of meteorological data shows that the high ozone days were associated with large-scale stagnation, intense solar radiation, and minimum rainfall. Large-scale back trajectories indicate a slow-moving/re-circulating airmass during the episodic days. Examination of chemical data shows that the observed daytime high ozone concentrations were due to downward mixing of ozone-rich air, in situ photochemical formation, and in some cases, advection to the site of aged plumes. The very high CO levels (and high CO to NO_x ratios) were found to coincide with many of the ozone episodes, suggesting a contribution from sources of emission involving incomplete combustion. It is suggested that the burning of biomass (e.g., biofeuls and crop residues) may be an important source for the observed high CO and O₃ values.     

A simple semi-empirical photochemical model for the simulation of ozone concentration in the Seoul metropolitan area in Korea

O₃ concentrations were simulated over the Seoul metropolitan area in Korea using a simple semi-empirical reaction (SEGRS) model which consists of generic reaction set (GRS), photochemical reaction set, and the diagnostic wind field generation model. The aggregated VOC emission strength was empirically scaled by the comparison of the simulated slope of (O₃–2NO–NO₂) concentration as a function of cumulative actinic light flux against measurements on high surface ozone concentration days with the relatively weak easterly geostrophic winds at the 850 hPa level in summer when the effect of horizontal advection was fairly small. The results indicated that the spatial distribution patterns and temporal variations of spatially averaged ground-level ozone concentrations were quite well simulated compared with those of observations with the modified volatile organic compound (VOC) emission strength. The diurnal trend of the surface ozone concentration and the maximum concentration compared observations were also quite reasonably simulated. However, the maximum ozone concentration occurring time at Seoul lagged about 2 h and the ozone concentration in the suburban area was slightly overestimated in the afternoon due to the influx of high ozone concentration from the urban area. It was found that the SEGRS model could be effectively used to simulate or predict the ground-level ozone concentration reasonably well without heavy computational cost provided the emission of ozone precursors are given.     

Ground-level ozone and ozone vertical profile measurements close to the foothills of the Guadarrama mountain range (Spain)

Continuous measurements of ozone vertical profiles, OVP, in the low troposphere (around 500–2400 m) using an unattended commercial ozone profiler DIAL, were conducted during June–July 2004 in Segovia, SG, a small city in the upper plateau located close to the foothills of the Guadarrama mountain range, Guadarrama, in the Central Massif. The data obtained over almost 37 complete days have enabled us to characterise the ozone vertical exchange, describe the phenomenology of the main ozone peaks, OP, recorded in the city and their relationship with ozone transport/formation from the gas precursor emissions of the greater Madrid area across Guadarrama. To achieve the last objective concurrent measurements of ground-level ozone in SG and a representative monitoring station upwind from Guadarrama, Buitrago de Lozoya, BL, have been used. 72.2% of the concurrent maximum diurnal ozone peaks exceeding the 95 percentile hourly value in SG (OPSG) and BL (OPBL) were linked to ozone transport and formation from the greater Madrid area towards Guadarrama. An estimate of the contribution of the greater Madrid area on OPSG yielded 28 μg m⁻³.The most prominent ozone vertical stratification was linked to the mixing height, MH, and a frequent nocturnal stable layer formed, NSL. Three small ozone enriched-layers were identified at mean heights of 500, 700 and 1000 m, respectively. Ozone tended to decline versus altitude. The hourly patterns of the three layers showed two peak occurrences of similar amplitude in the early morning, 7–8 h, and mid-afternoon, 14–16 h. A minimum was also observed during daytime, 10–11 h, its origin being attributed to a dilution process induced by the “chimney effect” caused by the slopes heating during this period.The comparison between OPSG, and the maximum diurnal ozone peaks in the first layer, OL1P, showed a satisfactory relationship, correlation coefficient, r, of the linear fit 0.77, and comparable mean values, 127 and 130 μg m⁻³, respectively, revealing the presence of an uniform ozone vertical distribution in the 500 m atmospheric layer above ground level during mid-afternoon.     

Determination of primary and secondary sources of organic acids and carbonaceous aerosols using stable carbon isotopes

Stable carbon isotope ratio (δ¹³C) data can provide important information regarding the sources and the processing of atmospheric organic carbon species. Formic, acetic and oxalic acid were collected from Zurich city in August–September 2002 and March 2003 in the gas and aerosol phase, and the corresponding δ¹³C analysis was performed using a wet oxidation method followed by isotope ratio mass spectrometry. In August, the δ¹³C values of gas phase formic acid showed a significant correlation with ozone (coefficient of determination (r²) = 0.63) due to the kinetic isotope effect (KIE). This indicates the presence of secondary sources (i.e. production of organic acids in the atmosphere) in addition to direct emission. In March, both gaseous formic and acetic acid exhibited similar δ¹³C values and did not show any correlation with ozone, indicating a predominantly primary origin. Even though oxalic acid is mainly produced by secondary processes, the δ¹³C value of particulate oxalic acid was not depleted and did not show any correlation with ozone, which may be due to the enrichment of ¹³C during the gas - aerosol partitioning.The concentrations and δ¹³C values of the different aerosol fractions (water soluble organic carbon, water insoluble organic carbon, carbonate and black carbon) collected during the same period were also determined. Water soluble organic carbon (WSOC) contributed about 60% to the total carbon and was enriched in ¹³C compared to other fractions indicating a possible effect of gas - aerosol partitioning on δ¹³C of carbonaceous aerosols. The carbonate fraction in general was very low (3% of the total carbon).     

A diagnostic comparison of measured and model-predicted speciated VOC concentrations

This study compares speciated model-predicted concentrations (i.e., mixing ratios) of volatile organic compounds (VOCs) with measurements from the Photochemical Assessment Monitoring Stations (PAMS) network at sites within the northeastern US during June–August of 2006. Measurements of total non-methane organic compounds (NMOC), ozone (O₃), oxides of nitrogen (NO_x) and reactive nitrogen species (NO_y) are used for supporting analysis. The measured VOC species were grouped into the surrogate classes used by the Carbon Bond IV (CB4) chemical mechanism. It was found that the model typically over-predicted all the CB4 VOC species, except isoprene, which might be linked to overestimated emissions. Even with over-predictions in the CB4 VOC species, model performance for daily maximum O₃ was typically within ±15%. Analysis at an urban site in NY, where both NMOC and NO_x data were available, suggested that the reasonable ozone performance may be possibly due to compensating overestimated NO_x concentrations, thus modulating the NMOC/NO_x ratio to be in similar ranges as that of observations.     

Degradation of tert-butyl formate and its intermediates by an ozone/UV process

In this paper, the oxidation of tert-butyl formate (TBF) in aqueous solution by an ozone/UV process was described. The oxidation process was investigated experimentally in a semibatch reactor. The results of the study indicated that the ozone/UV process was very effective in oxidizing TBF. tert-Butyl alcohol (TBA), hydroxy-iso-butyraldehyde (HiBA), acetone, formaldehyde, and formic acid were identified as major primary intermediates during the oxidation of TBF. About 90% organic carbon balance was obtained indicating that most reaction intermediates have been identified and quantified. Some of the primary intermediates were also oxidized in the ozone/UV system. Accordingly, HiBA, acetone, formaldehyde, and formic acid were the primary intermediates of TBA oxidation. The oxidation of acetone in the ozone/UV system generated formaldehyde, pyruvaldehyde, acetic acid, formic acid as primary intermediates. It was also observed that the reaction intermediates formed during the oxidation of TBF react well in the ozone/UV system and complete mineralization could be achieved by the process.     

A comparison of PAMS and air toxics measurements

One of the requirements of the 1990 Clean Air Act Amendments (CAA) is that 1-h ozone nonattainment areas that are classified severe or higher category are required to operate a network of photochemical assessment monitors (PAMS) to provide hourly measurements of volatile organic compounds (VOCs) comprising of Carbon number <12 (C2–C12), along with carbonyl measurements at 3-h intervals during the summer ozone season. Often collocated with PAMS are 24-h-integrated canister and cartridge-based measurements of selected air toxic compounds, thereby providing an opportunity for inter-comparison and validation of both sets of data. In this study, we report such a comparison and estimates of trend for benzene, m-, p- and o-xylene, toluene, ethylbenzene, 1,2,4-trimethylbenzene, formaldehyde and acetaldehyde at Bronx, NY. The analysis shows that hourly PAMS and 24-h-integrated air toxics are in good agreement with each other exhibiting similar trends and that the PAMS with the higher temporal resolution offers information on excursions of the toxic compounds that would be quite useful in assessment of acute health effects. These findings were also found to be applicable to other locations such as South De Kalb, GA; Gary, IN and Lynn, MA.     

Comparison of measured and modeled surface ozone concentrations at two different sites in Europe during the solar eclipse on August 11, 1999

The effects of the solar eclipse on 11 August 1999 on surface ozone at two sites, Thessaloniki, Greece (urban site) and Hohenpeissenberg, Germany (elevated rural site) are investigated in this study and compared with model results. The eclipse offered a unique opportunity to test our understanding of tropospheric ozone chemistry and to investigate with a simple photochemical box model the response of surface ozone to changes of solar radiation during a photolytical perturbation such as the solar eclipse. The surface ozone measurements following the eclipse display a decrease of around 10–15 ppbv at the urban station of Eptapyrgio at Thessaloniki while at Hohenpeissenberg, the actual ozone data do not show any clear effect of eclipse on surface ozone. For Thessaloniki, the model results suggest that solely photochemistry can account for a significant amount of the observed surface ozone decrease during the eclipse but transport effects mask part of the photochemical effect of eclipse on surface ozone. For Hohenpeissenberg, the box model predicted an ozone decrease, due to the eclipse, of about 2 ppbv in relative agreement with the magnitude of the observed ozone decrease from the 2 h moving average while at the same time it inhibits the foreseen diurnal ozone increase. However, this modeled ozone decrease during the eclipse is small compared to the diurnal ozone variability due to transport effects, and hence, transport really masks such relative small changes. The different magnitude of the surface ozone decrease between the two sites indicates mainly the role of the NO_x levels. Measured and modeled NO and NO₂ concentrations at Hohenpeissenberg during the eclipse are also compared and indicate that the partitioning of NO and NO₂ in NO_x is influenced clearly from the eclipse. This is not observed at Thessaloniki due to local NO_x sources.     

Ozone Concentrations in the Central Wasatch Mountains of Utah

Abstract

In the Salt Lake Valley, a June through August SUM60 value (sum of hourly average ozone concentrations ≥60 parts per billion by volume [ppbv]) of 25,000 ppbv-hr was exceeded in 9 yr between 1978 and 1998. Ozone concentrations in the nearby Central Wasatch Mountains were monitored to determine the potential for vegetation injury. The SUM60 value of 19,000 ppbv-hr in these mountains and peak hourly concentrations >100 ppbv suggests that ozone-sensitive species may be injured. Ozone concentrations in the mountains were greatest during periods of strong upslope winds from the Salt Lake Valley. Both SUM60 values and hourly average concentrations in the Central Wasatch Mountains were strongly correlated with those in the Salt Lake Valley, suggesting that data from valley stations could be used to estimate ozone in the mountains.     

An observational study of the HONO–NO2 coupling at an urban site in Guangzhou City,South China

The temporal behavior of HONO and NO₂ was investigated at an urban site in Guangzhou city, China, by means of a DOAS system during the Pearl River Delta 2006 intensive campaign from 10 to 24 July 2006. Within the whole measurement period, unexpected high HONO mixing ratios up to 2 ppb were observed even during the day. A nocturnal maximum concentration of about 8.43 ± 0.4 ppb was detected on the night of 24 July 2006. Combining the data simultaneously observed by different instruments, the coupling of HONO–NO₂ and the possible formation sources of HONO are discussed. During the measurement period, concentration ratios of HONO to NO₂ ranged from (0.03 ± 0.1) to (0.37 ± 0.09), which is significantly higher than previously reported values (0.01–0.1). Surprisingly, in most cases a strong daytime correlation between HONO and NO₂ was found, contrary to previous observations in China. Aerosol was found to have a minor impact on HONO formation during the whole measurement period. Using a pseudo steady state approach for interpreting the nocturnal conversion of NO₂ to HONO suggests a non-negligible role of the relative humidity for the heterogeneous HONO formation from NO₂.     

Understanding the contributions of anthropogenic and biogenic sources to CO enhancements and outflow observed over North America and the western Atlantic Ocean by TES and MOPITT

We investigate the effects of anthropogenic and biogenic sources on tropospheric CO enhancements and outflow over North America and the Atlantic during July–August 2006, the 3rd warmest summer on record. The analysis is performed using the 3D Regional chEmical trAnsport Model (REAM), satellite data from TES on the Aura satellite, MOPITT on the Terra satellite and surface monitor data from the SEARCH network. The satellite measurements of CO provide insight into the location of regional CO enhancements along with the ability to resolve vertical features. Satellite and surface monitor data are used to compare with REAM, illustrating model's ability to reproduce observed CO concentrations. The REAM model used in this study features CO emissions reduced by 50% from the 1999 EPA NEI and biogenic VOC emissions scaled by EPA-observed isoprene concentrations (20% reduction). The REAM simulations show large variations in surface CO, lower tropospheric CO and column CO, which are also observed by the surface observations and satellite data. Over the US, during July–August 2006, the model estimates monthly CO production from anthropogenic sources (5.3 and 5.1 Tg CO) is generally larger than biogenic sources (4.3 and 3.5 Tg CO). However, the model shows that for very warm days, biogenic sources produce as much CO as anthropogenic sources, a result of increased biogenic production due to warmer temperatures. The satellite data show CO outflow occurs along the East Coast of the US and Canada in July and is more broadly distributed over the Atlantic in August. REAM results show the longitudinally exported CO enhancements from anthropogenic sources (3.3 and 3.9 Tg CO) are larger than biogenic sources (2.8 and 2.7 Tg CO) along the eastern boundary of REAM for July–August 2006. We show that when compared with the impacts of both sources on increasing tropospheric CO exports, the relative impacts in August are greater than in July because of preferable outflow transport.     

Long-term changes in the tropospheric column ozone from the ozone soundings over Europe

The tropospheric column of ozone is analyzed from the measurements of the vertical profile of ozone by balloon-born ozonesondes. The data base includes ∼16,000 ozone profiles collected above six European stations—three of them have begun the ozonesoundings since 1970. We present a trend analysis (with data up to 2005) focusing on detection of the long-term tropospheric ozone variability over the European network. The ozone time series have been examined separately for each station and season (DJF, MAM, JJA, SON) using a flexible trend model. A trend component of the model is taken as a smooth curve without a priori defined shape. A large increase in the European tropospheric ozone since the beginning of the 1970s (net change of ∼10% in summers and ∼30% in winters) and a kind of stabilization in the early 1990s have been corroborated by the study. This pattern comes from the most extensive data set of ozonesoundings over Hohenpeissenberg and Payern. The decadal differences in the trend pattern between these and other European stations are disclosed. The results of a stepwise regression model using various characteristics of the ozone and temperature profiles as explanatory variables for the tropospheric column ozone (TCO₃) variations show that the ozone changes may be reconstructed using the ozone mixing ratio at 500 hPa, the thermal tropopause (TT) height, and the difference between ozonepause and TT heights. It appears that the last two factors induce 20–30% of the net TCO₃ change over Hohenpeissenberg in the 1970–2004 period.     

Evaluation of the effect of long-range transport of air pollutants on coastal atmospheric monitoring sites in and around Taiwan

Long-range transport of pollution outflow from Asian mainland has been noticed and expected to play a significant role in Pacific background. Since 1993 the Taiwanese Environmental Protection Administration (TEPA) is conducting ground-based observations of various particulate and gaseous pollutants at 74 monitoring stations in Taiwan. One of these stations, Heng-Chun at the south coast of Taiwan can be considered as a background station with only negligible amounts of local pollution, and another one, Wan-Li at the north coast, predominantly receives air that has not passed over Taiwan, so that background air can be analysed by means of sectorisation. In this work, the sectorised 13-year time series of measurements of CO, SO₂, O₃, NO_x and PM₁₀, from the Wan-Li station are presen and compared to data from the Heng-Chun station and another TEPA background station off the coast of mainland China, Ma-Zu. The CO and O₃ measurements are also compared to data from the Yonaguni station, a Pacific island site, part of the Global Atmospheric Watch (GAW) network.The similarity of the sectorised data from the Wan-Li station with the data of the other station indicates that atmospheric measurements from the Wan-Li site can be used to make inferences about trends in western Pacific background air pollution and the effect of long-range transport of pollutants. The measurement time series from 1993 to 2006 do not indicate a significant trend in the monthly mean O₃ concentrations in accordance with other research about ozone in tropical latitudes. An increasing trend in CO concentrations of 2.8% per annum is observed between 1999 and 2006 for long-range transport to northern Taiwan, and a doubling of the SO₂ and NO_x concentrations observed at the Wan-Li and Heng-Chun sites within the period 2001–2006. SO₂ concentrations are found to quadruple at Ma-Zu within the same period. The data suggest that pollution from the Asian mainland enhances significantly the background air pollution over the Pacific.     

Uncertainties in predicted ozone concentrations due to input uncertainties for the UAM-V photochemical grid model applied to the July 1995 OTAG domain

The photochemical grid model, UAM-V, has been used by regulatory agencies to make decisions concerning emissions controls, based on studies of the July 1995 ozone episode in the eastern US. The current research concerns the effect of the uncertainties in UAM-V input variables (emissions, initial and boundary conditions, meteorological variables, and chemical reactions) on the uncertainties in UAM-V ozone predictions. Uncertainties of 128 input variables have been estimated and most range from about 20% to a factor of two. 100 Monte Carlo runs, each with new resampled values of each of the 128 input variables, have been made for given sets of median emissions assumptions. Emphasis is on the maximum hourly-averaged ozone concentration during the 12–14 July 1995 period. The distribution function of the 100 Monte Carlo predicted domain-wide maximum ozone concentrations is consistently close to log-normal with a 95% uncertainty range extending over plus and minus a factor of about 1.6 from the median. Uncertainties in ozone predictions are found to be most strongly correlated with uncertainties in the NO₂ photolysis rate. Also important are wind speed and direction, relative humidity, cloud cover, and biogenic VOC emissions. Differences in median predicted maximum ozone concentrations for three alternate emissions control assumptions were investigated, with the result that (1) the suggested year-2007 emissions changes would likely be effective in reducing concentrations from those for the year-1995 actual emissions, that (2) an additional 50% NO_x emissions reductions would likely be effective in further reducing concentrations, and that (3) an additional 50% VOC emission reductions may not be effective in further reducing concentrations.