Anthropogenic platinum fluxes: Quantification of sources and sinks, and outlook

Employing the data available to date, anthropogenic Pt fluxes are calculated for Germany with special emphasis on the Pt emitted by cars equipped with catalytic converters. Pt fluxes are quantified using five different methods (street deposition, automobile emission rate, sewage sludges, atmospheric load, industrial consumption). During the first and the second methods, approx. 100 kg of emitted Pt are seen to result for both for the mid 1990’s. Up to the year 2018, a total of 2100 kg of Pt will be emitted by cars equipped with catalytic converters. The diffuse atmospheric Pt deposition amounts to 0.73 – 4.4 μg/m²y or 260 kg Pt/year. Industrial sources emitting Pt into the atmosphere are likely but difficult to quantify. The enrichment of Pt in soils during agriculture fertilization with sewage sludges and during diffuse atmospheric deposition result in a level of 46 – 460 ng/kg up to the year 2018. Although this is slightly below the geogenic background, a comparison with the pollution history of Pb implies that forthcoming environmental Pt enrichment should not be neglected.     

Platinum emission rate of automobiles with catalytic converters

Inconsistent data presently available on the platinum emission rate of cars in Germany equipped with catalytic converters are evaluated. Automobile sources of Pt other than autocatalysts are quantified and found to be 1–6 orders of magnitudes lower than the Pt emissions attributed to catalytic converters. A transfer of emission rates derived from test stand experiments to more realistic street conditions reaches 0.8 μg Pt/km. In this manner, data from test stand experiments and from environmental investigations meet in the range of 0.5–0.8 μg Pt/km.     

Implications of climate change for the stomatal flux of ozone: a case study for winter wheat

Climate change factors such as elevated CO2 concentrations, warming and changes in precipitation affect the stomatal flux of ozone (O3) into leaves directly or indirectly by altering the stomatal conductance, atmospheric O3 concentrations, frequency and extent of pollution episodes and length of the growing season. Results of a case study for winter wheat indicate that in a future climate the exceedance of the flux-based critical level of O3 might be reduced across Europe, even when taking into account an increase in tropospheric background O3 concentration. In contrast, the exceedance of the concentration-based critical level of O3 will increase with the projected increase in tropospheric background O3 concentration. The influence of climate change should be considered when predicting the future effects of O3 on vegetation. There is a clear need for multi-factorial, open-air experiments to provide more realistic information for O3 flux-effect modelling in a future climate.     

一次光化学污染过程中O3和NOx的垂直梯度观测研究

为了研究2008年北京奥运会前期污染物浓度变化特征,对北京气象塔3层高度上的大气污染物（NO2和O3）进行加强观测,分析其变化特征。观测结果表明,由于北京奥运会前期采取了严格的空气质量控制措施,NO2浓度相对车辆限行前下降了45.3%,且随着高度递增逐渐降低;O3浓度最大值和日均值有所降低,其最大值出现时间较10年前提前了12 h,且有4 h左右处于相对平稳状态。O3浓度峰值主要是受NO2的控制,O3浓度峰值出现时间提前反映出北京大气氧化效率不断提高。对于观测期间出现光化学污染事件,利用同期气象资料和大气污染监测数据分析,发现造成这次大气污染的主要原因是气象因子：地面多处于弱高压场控制中,大气层结稳定,风力较弱（小于2 m/s）,并伴随着连续高温、强辐射和低湿。     

The acanthocephalan Paratenuisentis ambiguus as a sensitive indicator of the precious metals Pt and Rh from automobile catalytic converters

Recent studies revealed that intestinal acanthocephalans of fish can accumulate heavy metals to concentrations orders of magnitude higher than those in the host tissues or the aquatic environment. This significant heavy metal accumulation by acanthocephalans, even surpassing that of established free living accumulation bioindicators, encouraged us to study the bioavailability of the platinum-group-metals (PGM) Pt and Rh for parasites. These precious metals are used in catalytic converters of cars for exhaust gas purification in Europe since the early 1980s. In addition to the beneficial effect in reducing the emission of CHx, CO and NOx of cars there is an increasing emission of these metals. However, it still remains unclear if these elements become accumulated in the biosphere and whether they affect the health of organisms. The present study reveals that in European eels (Anguilla anguilla) naturally infected with the eoacanthocephalan parasite Paratenuisentis ambiguus and experimentally exposed to ground catalytic converter material, the parasites take up and accumulate the catalytic active metals Pt and Rh whereas in the examined host tissues we found no metal uptake. Compared with the PGM concentrations in the water the worms contained 1600 times higher Rh and 50 times higher Pt concentrations. Thus, the parasites can be used as sentinel organisms reflecting even very low levels of precious metals.     

Long-term efficiency of catalytic converters operating in Mexico City

A 1999 ordinance by the Government of Mexico City bans 1993 model-year vehicles from on-road operation if their catalytic converters are not replaced with new ones. To validate the benefits of this action, we examined three issues related to exhaust emissions of vehicles equipped with catalytic converters. After selecting representative fleets of in-use vehicles, a comparison between emissions and catalyst efficiency in cars with two categories of exhaust emission limits was carried out. For that purpose, two fleets were selected, each made up of 10 vehicles run under similar conditions. A third, larger fleet with emissions control systems was used to evaluate and simulate real-world conditions of vehicles in a controlled laboratory. Finally, the aging effect on the catalytic converter was studied on vehicles run for 100,000 km, replacing their old emission control devices for new ones. The 1991-1992 model-year vehicles showed a high percentage of compliance with the corresponding emissions standard (90%) in comparison with 1993 model-year and later vehicles (Tier 0). However, NOx emissions were higher for the newer vehicles. Fifty percent of the 1991-1992 model-year vehicles evaluated under the official inspection/maintenance (I/M) procedure did not meet the regulated emissions standard when the results were compared with those of the U.S. Federal Test Procedure FTP-75. Our results suggest that the replacement of old catalytic converters with new ones will have little effect on decreasing polluting emissions because these vehicles were in very bad mechanical condition. Results of catalytic activity as a function of mileage indicated inefficient catalyst performance for the fleets tested. All pollutant conversions were below 90% efficiency, and they deteriorated by an average of 30% after the vehicles were run for 100,000 km.     

Monuments as sampling surfaces of recent traffic pollution

Background, aim and scope  

A new approach towards monuments, considering them as a passive sampler of pollution, is presented. Cultural Heritage objects suffer daily the damages of environmental pollution, especially in those areas interested by heavy traffic. Since monuments undergo only periodic conservation or maintenance works, surfaces are able to accumulate atmospheric deposit and to record changes in its composition. An optimised analytical protocol was developed in order to quantify platinum and rhodium at trace level on surfaces. The two elements have become tracers of automobile emissions in recent years, since the introduction of catalytic converters, and could have catalytic effects on the decay reactions of natural and artificial stone materials. As a first case study, the cement mortar surfaces of a twentieth century monument, the Camerlata Fountain, in Como (Italy) were investigated.     

Mycorrhizal mediation of plant response to atmospheric change: Air quality concepts and research considerations

The term 'global climate change' encompasses many physical and chemical changes in the atmosphere that have been induced by anthropogenic pollutants. Increases in concentrations of CO2 and CH4 enhance the 'greenhouse effect' of the atmosphere and may contribute to changes in temperature and precipitation patterns at the earth's surface. Nitrogen oxides and SO2 are phytotoxic and also react with other pollutants to produce other phytotoxins in the troposphere such as O3 and acidic substances. However, release of chlorofluorocarbons into the atmosphere may cause depletion of stratospheric O3, increasing the transmittance of ultraviolet-B (UV-B) radiation to the earth's surface. Increased intensities of UV-B could affect plants and enhance photochemical reactions that generate some phytotoxic pollutants. The role of mycorrhizae in plant responses to such stresses has received little attention. Although plans for several research programs have acknowledged the importance of drought tolerance and soil fertility in plant responses to atmospheric stresses, mycorrhizae are rarely targeted to receive specific investigation. Most vascular land plants form mycorrhizae, so the role of mycorrhizae in mediating plant responses to atmospheric change may be an important consideration in predicting effects of atmospheric changes on plants in managed and natural ecosystems.     

Ozone artifacts and carbonyl measurements using Tenax GR, Tenax TA, Carbopack B, and Carbopack X adsorbents

Four popular thermally desorbable adsorbents used for air sampling (Tenax TA, Tenax GR, Carbopack B, and Carbopack X) are examined for the potential to form artifacts with ozone (O3) at environmental concentrations. The performance of these adsorbents for the ketone and aldehyde species identified as O3-adsorbent artifacts was also characterized, including recovery, linearity, and method detection limits (MDLs). Using gas chromatography/mass spectrometry, 13 different artifacts were identified and confirmed for both Tenax TA and Tenax GR, 9 for Carbopack B, but none for Carbopack X. Several O3 artifacts not reported previously were identified, including: pentanal, 3-hexanone, 2-hexanone, hexanal, 3-heptanone, and heptanal with Tenax TA; pentanal, 3-hexanone, 2-hexanone, hexanal, and 3-heptanone on Tenax GR; and 1-octene and 1-nonene with Carbopack B. Levels of straight-chain aldehyde artifacts rapidly diminished after a few cycles of adsorbent conditioning/O3 exposure, and concentrations could be predicted using a first-order model. Phenyl-substituted carbonyl artifacts (benzaldehyde and acetophenone) persisted on Tenax TA and GR even after 10 O3 exposure-conditioning cycles. O3 breakthrough through the adsorbent bed was most rapid in adsorbents that yielded the highest levels of artifacts. Overall, artifact composition and concentration are shown to depend on O3 concentration and dose, conditioning method, and adsorbent type and age. Calibrations showed good linearity, and most compounds had reasonable recoveries, for example, 90 +/- 15% for Tenax TA, 97 +/- 23% for Tenax GR, 101 +/- 24% for Carbopack B, and 79 +/- 25% (91 +/- 9% for n-aldehydes) for Carbopack X. Benzeneacetaldehyde recovery was notably poorer (22-63% across the four adsorbents). MDLs for several compounds were relatively high, up to 5 ng. By accounting for both artifact formation and method performance, this work helps to identify which carbonyl compounds can be measured using thermally desorbable adsorbents and which may be prone to bias because of the formation of O3-adsorbent artifacts.     

Long-Term Efficiency of Catalytic Converters Operating in Mexico City

ABSTRACT

A 1999 ordinance by the Government of Mexico City bans 1993 model-year vehicles from on-road operation if their catalytic converters are not replaced with new ones. To validate the benefits of this action, we examined three issues related to exhaust emissions of vehicles equipped with catalytic converters. After selecting representative fleets of in-use vehicles, a comparison between emissions and catalyst efficiency in cars with two categories of exhaust emission limits was carried out. For that purpose, two fleets were selected, each made up of 10 vehicles run under similar conditions. A third, larger fleet with emissions control systems was used to evaluate and simulate real-world conditions of vehicles in a controlled laboratory. Finally, the aging effect on the catalytic converter was studied on vehicles run for 100,000 km, replacing their old emission control devices for new ones.

The 1991-1992 model-year vehicles showed a high percentage of compliance with the corresponding emissions standard (90%) in comparison with 1993 model-year and later vehicles (Tier 0). However, NO_x emissions were higher for the newer vehicles. Fifty percent of the 1991-1992 model-year vehicles evaluated under the official inspection/maintenance (I/M) procedure did not meet the regulated emissions standard when the results were compared with those of the U.S. Federal Test Procedure     

The role of halogen species in the troposphere

While the role of reactive halogen species (e.g. Cl, Br) in the destruction of the stratospheric ozone layer is well known, their role in the troposphere was investigated only since their destructive effect on boundary layer ozone after polar sunrise became obvious. During these 'Polar Tropospheric Ozone Hole' events O(3) is completely destroyed in the lowest approximately 1000 m of the atmosphere on areas of several million square kilometres. Up to now it was assumed that these events were confined to the polar regions during springtime. However, during the last few years significant amounts of BrO and Cl-atoms were also found outside the Arctic and Antarctic boundary layer. Recently even higher BrO mixing ratios (up to 176 ppt) were detected by optical absorption spectroscopy (DOAS) in the Dead Sea basin during summer. In addition, evidence is accumulating that BrO (at levels around 1-2 ppt) is also occurring in the free troposphere at all latitudes.In contrast to the stratosphere, where halogens are released from species, which are very long lived in the troposphere, likely sources of boundary layer Br and Cl are autocatalytic oxidation of sea salt halides (the 'Bromine Explosion'), while precursors of free tropospheric BrO and coastal IO probably are short-lived organo-halogen species. At the levels suggested by the available measurements reactive halogen species have a profound effect on tropospheric chemistry: In the polar boundary layer during 'halogen events' ozone is usually completely lost within hours or days. In the free troposphere the effective O(3)-losses due to halogens could be comparable to the known photochemical O(3) destruction. Further interesting consequences include the increase of OH levels and (at low NO(X)) the decrease of the HO(2)/OH ratio in the free troposphere.     

Effects of NO2 and SO2 on selective catalytic reduction of nitrogen oxides by ammonia

The selective catalytic reduction (SCR) characteristics of NO and NO(2) over V(2)O(5)-WO(3)-MnO(2)/TiO(2) catalyst using ammonia as a reducing agent have been determined in a fixed-bed reactor at 200-400 degrees C. The presence of NO(2) enhances the SCR activity at lower temperatures and the optimum ratio of NO(2)/NO(x) is found to be 0.5. During the SCR reactions, there are some side reactions occurred such as ammonia oxidation and N(2)O formation. At higher temperatures, the selective catalytic oxidation of ammonia and the nitrous oxide formation compete with the SCR reactions. The denitrification (DeNO(x)) conversion decreases at lower temperatures but it increases at higher temperatures with increasing SO(2) concentration. The presence of SO(2) in the feeds inhibits N(2)O formation.     

Beryllium-7 measurements in the Houston and Phoenix urban areas: an estimation of upper atmospheric ozone contributions

Natural radionuclides have been proposed as a means of assessing the transport of ozone (O3) and aerosols in the troposphere. Beryllium-7 (7Be) is produced in the upper troposphere and lower stratosphere by the interaction of cosmogenic particles with atmospheric nitrogen and oxygen. 7Be has a 53.29-day half-life (478 keV gamma) and is known to attach to fine particles in the atmosphere once it is formed. It has been suggested that O3 from aloft can be transported into rural and urban regions during stratospheric-tropospheric folding events leading to increased background levels of O3 at the surface. 7Be can be used as a tracer of upper atmospheric air parcels and the O3 associated with them. Aerosol samples with a 2.5-microm cutoff were collected during 12-hr cycles (day/night) for a 30-day period at Deer Park, TX, near Houston, in August-September of 2000, and at Waddell, AZ, near Phoenix, in June-July of 2001. A comparison of 7Be levels with 12-hr O3 averages and maxima shows little correlation. Comparison of nighttime and daytime O3 levels indicate that during the day, when mixing is anticipated to be higher, the correlation of 7Be with O3 in Houston is approximately twice that observed at night. This is consistent with mixing and with the anticipated loss of O3 by reaction with nitric oxide (NO) and dry deposition. At best, 30% of the O3 variance can be explained by the correlation with 7Be for Houston, less than that for Phoenix where no significant correlation was seen. This result is consistent with the intercept values obtained for 7Be correlations with either O3 24-hr averages or O3 12-hr maxima and is also in the range of the low O3 levels (25 ppb) observed at Deer Park during a tropical storm event where the O3 is attributable primarily to background air masses. That is, maximum background O3 level contributions from stratospheric sources aloft are estimated to be in the range of 15-30 ppb in the Houston, TX, and Phoenix, AZ, area, and levels above these are because of local tropospheric photochemical production.     

Identification of a potential source of chloroform in urban air: Preliminary Communication

A new potential source of elevated chloroform (CHCl₃) concentrations in urban air is reported. The exhaust gases from gasoline internal combustion engines operated on conventional “leaded” fuel and not equipped with catalytic converters contain parts-per-billion concentrations of chloroform which can, in congested urban areas, contribute significantly to the ambient concentration of chloroform. Exhaust gases from engines burning conventional “leaded” gasoline contain much higher levels of chloroform than do exhaust gases from engines equipped with catalytic converters and operating on “nonleaded” gasoline.     

Estimation of the Natural Background of Ozone Present at Surface Rural Locations

The natural background in the ozone concentration at rural locations in the United States and western Europe has been estimated by use of several approaches. The approaches utilized include the following: (1) historical trends in ozone concentration measurements, (2) recent ozone measurements at remote sites, (3) use of tracers of air originating in the stratosphere or upper troposphere and (4) results from applications of tropospheric photochemical models. While each of these approaches has its own limitations it appears that the natural background of ozone during the warmer months of the year is in the range of 10 to 20 ppb. Most of the ozone originating in the lower stratosphere or upper troposphere is lost by chemical or physical removal processes as well as undergoing dilution by air in the lower troposphere before reaching ground level rural locations. Lower tropospheric photochemical processes, those below 5 km, are likely to account for most of the ozone measured at rural locations during the warmer months of the year.

A key aspect to improved quantitation of the contributions from lower tropospheric photochemical processes to ozone concentrations continues to be more extensive atmospheric measurements of the distribution of reactive species of nitrogen. The emission densities of anthropogenic sources of NO_x are known to be highly variable over populated areas of continents as well as between continental areas and the oceans. The emission densities of biogenic sources of NO_x are small, likely to be highly variable, but poorly quantitated. These wide variations indicate the need for use of three dimensional tropospheric photochemical models over large continental regions.

Available results do indicate higher efficiencies for ozone formation at lower NO_x concentrations, especially below 1 ppb.     

Effects of enhanced O3 and CO2 enrichment on plant characteristics in wheat and corn

The effects of CO(2) enrichment and O(3) induced stress on wheat (Triticum aestivum L.) and corn (Zea mays L.) were studied in field experiments using open-top chambers to simulate the atmospheric concentrations of these two gases that are predicted to occur during the coming century. The experiments were conducted at Beltsville, MD, during 1991 (wheat and corn) and 1992 (wheat). Crops were grown under charcoal filtered (CF) air or ambient air + 40 nl liter(-1) O(3) (7 h per day, 5 days per week) having ambient CO(2) concentration (350 microl liter(-1) CO(2)) or + 150 microl liter(-1) CO(2) (12 h per day.). Averaged over O(3) treatments, the CO(2)-enriched environment had a positive effect on wheat grain yield (26% in 1991 and 15% in 1992) and dry biomass (15% in 1991 and 9% in 1992). Averaged over CO(2) treatments, high O(3) exposure had a negative impact on wheat grain yield (-15% in 1991 and -11% in 1992) and dry biomass (-11% in 1991 and -9% in 1992). Averaged over CO(2) treatments, high O(3) exposure decreased corn grain yield by 9%. No significant interactive effects were observed for either crop. The results indicated that CO(2) enrichment had a beneficial effect in wheat (C(3) crop) but not in corn (C(4) crop). It is likely that the O(3)-induced stress will be diminished under increased atmospheric CO(2) concentrations; however, maximal benefits in crop production in wheat in response to CO(2) enrichment will not be materialized under concomitant increases in tropospheric O(3) concentration.     

Consistency of ozone and nitrogen oxides standards at tropospherically relevant mixing ratios

The absolute accuracy and long-term precision of atmospheric measurements hinge on the quality of the instrumentation and calibration standards. To assess the consistency of the ozone (O3) and nitrogen oxides (NO(x)) standards maintained at the National Institute of Standards and Technology (NIST), these standards were compared through the gas-phase titration of O3 with nitric oxide (NO). NO and O3 were monitored using chemiluminescence and UV absorption, respectively. Nitrogen dioxide (NO2) was monitored directly by laser-induced fluorescence and indirectly by catalytic conversion to NO, followed by chemiluminescence. The observed equivalent loss of both NO and O3 and the formation of NO2 in these experiments was within 1% on average over the range of 40-200 nmol mol(-1) of NO in excess O3, indicating that these instruments, when calibrated with the NIST O3 and NO standards and the NO2 permeation calibration system, are consistent to within 1% at tropospherically relevant mixing ratios of O3. Experiments conducted at higher initial NO mixing ratios or in excess NO are not in as good agreement. The largest discrepancies are associated with the chemiluminescence measurements. These results indicate the presence of systematic biases under these specific conditions. Prospects for improving these experiments are discussed.     

Tropospheric sources of NOx: lightning and biology.

Laboratory experiments to quantify the global production of NOx (NO + NO2) in the troposphere due to atmospheric lightning and biogenic activity in soil are presented. These laboratory experiments, as well as other studies, suggest that the global production of NOx by lightning probably ranges between 2 and 20 MT(N)y-1 of NO and is strongly dependent on the total energy deposited by lightning, a quantity not well-known. In our laboratory experiments, nitrifying micro-organisms is soil were found to be a significant source of both NO and nitrous oxide (N2O). The measured production ratio of NO to N2O averaged 2-3 for oxygen partial pressures of 0.5-10%. Extrapolating these laboratory measurements to the global scale, which is somewhat risky, suggests that nitrifying micro-organisms in soil may account for as much as 10 MT(N) y-1 of NO. Additional experiments with denitrifying micro-organisms gave an NO to N2O production ratio ranging from 2 to 4 for an oxygen partial pressure of 0.5% and a ratio of less than unity for oxygen partial pressures ranging from 1 to 20%. The production of NO and N2O, normalized with respect to micro-organism number indicates that the production of both NO and N2O by denitrifying micro-organisms is at least an order of magnitude less than production by nitrifying micro-organisms for the micro-organisms studied.     

A new model of tropospheric hydroxyl radical concentrations

A chemistry model of the global troposphere is presented which focuses on the hydroxyl radical, OH. Global distributions of OH are calculated based on known chemical reaction pathways, experimentally measured values of precursor species O3, H2O, NOx (defined as NO+NO2), CO, CH4, and actinic flux (which includes the effects of cloud cover and O3 column absorption). Model grid resolution is 1 km in altitude by 10 degrees latitude, and zonally divided into land or ocean. Species are calculated as seasonal averages. Global annual mean OH in the troposphere (up to 14 km altitude) is calculated to be 9.2 x 10(5) molcm(-3) with averages of 9.8 x 10(5) in the northern hemisphere, and 8.5 x 10(5) in the southern hemisphere. Global CO and CH(4) oxidation rates by OH are calculated to be 1840 Tgyear(-1) and 580 Tgyear(-1), respectively. OH is found to be most sensitive to O3 and H2O concentrations, as well as to the photolysis rate of O3 to O1D. Sensitivity of CO and CH4 oxidation rates to cloud presence shows an inverse relationship to cloud amount and optical depth. Model results are shown to be consistent with results from two other published models.