Atmospheric Environment (v.38, #25)

Formation of secondary organic aerosols from isoprene and its gas-phase oxidation products through reaction with hydrogen peroxide by Magda Claeys; Wu Wang; Alina C Ion; Ivan Kourtchev; András Gelencsér; Willy Maenhaut (4093-4098).
Aerosols produced over forests impair visibility and may affect climate by scattering and absorbing solar radiation and by serving as cloud condensation nuclei. Here, we introduce, to our knowledge, a new route to secondary organic aerosol formation from isoprene and its gas-phase oxidation products, methacrolein and methacrylic acid, namely, multiphase acid-catalysed oxidation with hydrogen peroxide, a perfect analogue to atmospheric sulphate formation. We demonstrate that the formation of major secondary organic aerosol components that are present in natural forest aerosols collected at K-puszta, Hungary, during the summer of 2003, namely, 2-methyltetrols and 2,3-dihydroxymethacrylic acid, can be explained by this mechanism.
Keywords: Secondary organic aerosol; Biogenic hydrocarbons; Isoprene; Photo-oxidation;

In this study, an integrated biogeochemical model (PnET-BGC) was used to evaluate the response of five forest ecosystems in the Adirondack and Catskill regions of New York to changes in atmospheric deposition and land disturbance. Model simulations showed that over the past 150 years, acidic deposition caused depletion of nutrient base cations (i.e., Ca2+, Mg2+), enhanced mobilization of aluminum (Al) and accumulation of sulfur (S) within the soil. Model simulations also showed that acidic deposition resulted in elevated concentrations of inorganic monomeric Al, sulfate (SO4 2−) and nitrate (NO3 ), and low values of pH and acid neutralizing capacity (ANC) in surface waters. Model results also indicated that forest harvests resulted in enhanced leaching of base cations and NO3 over the short term (∼5 yr). Over the long term, forest harvesting influences surface water NO3 and base cation concentrations, and pH and ANC. The model was also used to predict the responses of these forest ecosystems to three emission control scenarios. Model simulations indicated that under the 1990 Clean Air Act Amendment, these ecosystems showed little recovery after 2010. Additional reductions in strong acid inputs will result in significant benefits in terms of recovery from acidification. Under an aggressive control scenario, surface water ANC of these ecosystems was predicted to recover at rates ranging from 0.28 to 0.58 μeq l−1  yr−1.
Keywords: Acidic deposition; Land disturbance; Emission controls; Recovery; Modeling;

Volatile organic compound concentrations in ambient air of Kaohsiung petroleum refinery in Taiwan by Tsai-Yin Lin; Usha Sree; Sen-Hong Tseng; Kong Hwa Chiu; Chien-Hou Wu; Jiunn-Guang Lo (4111-4122).
The air quality assessment for volatile organic compounds (VOC) was conducted in and around Chinese petroleum corporation (CPC) refinery at Kaohsiung, located in southern Taiwan, during 2001 by collecting air samples at 26 sites. Benzene and toluene were detected as the most abundant VOC by both gas chromatography and ultra-violet differential optical absorption spectroscopy (UV-DOAS) techniques. BTXE concentrations showed day and night variations at some of the sampling site. The highest among the 26 sites for total concentration of VOC at CPC was 2506 ppbv near waste burning stack. High concentrations of VOC were also detected at the wastewater management area and the east gate of the plant. The values were 10–18 times higher than those probed in Kaohsiung city. The meteorological parameters such as wind speed and direction played vital roles in the distribution of ambient air VOC concentrations and affected the petrochemical complex emissions. The application of UV-DOAS for online monitoring of criteria pollutants appears feasible though the accuracy of the technique is not fully controlled.
Keywords: Volatile organics; Aromatic hydrocarbons; Petroleum refinery; DOAS; Taiwan;

This research assessed in-vehicle exposures to black carbon (BC) as an indicator of diesel particulate matter (DPM) exposures. Approximately 50 h of real-time Aethalometer BC measurements were made inside vehicles driven on freeway and arterial loops in Los Angeles and Sacramento. Video tapes of the driver's view were transcribed to record the traffic conditions, vehicles followed, and vehicle occupant observations, and these results were tested for their associations with BC concentration. In-vehicle BC concentrations were highest when directly following diesel-powered vehicles, particularly those with low exhaust pipe locations. The lowest BC concentrations were observed while following gasoline-powered passenger cars, on average no different than not following any vehicle. Because diesel vehicles were over-sampled in the field study, results were not representative of real-world driving. To calculate representative exposures, in-vehicle BC concentrations were grouped by the type of vehicle followed, for each road type and congestion level. These groupings were then re-sampled stochastically, in proportion to the fraction of statewide vehicle miles traveled (VMT) under each of those conditions. The approximately 6% of time spent following diesel vehicles led to 23% of the in-vehicle BC exposure, while the remaining exposure was due to elevated roadway BC concentrations. In-vehicle BC exposures averaged 6 μg m−3 in Los Angeles and the Bay Area, the regions with the highest congestion and the majority of the state's VMT. The statewide average in-vehicle BC exposure was 4 μg m−3, corresponding to DPM concentrations of 7–23 μg m−3, depending on the Aethalometer response to elemental carbon (EC) and the EC fraction of the DPM. In-vehicle contributions to overall DPM exposures ranged from approximately 30% to 55% of total DPM exposure on a statewide population basis. Thus, although time spent in vehicles was only 1.5 h day−1 on average, vehicles may be the most important microenvironment for overall DPM exposure.
Keywords: Exposure assessment; In-vehicle concentrations; Diesel vehicle emissions; Aethalometer;

Estimation and detection of flexible trends by Hans Visser (4135-4145).
Literature on the estimation and detection of linear trends in (environmental) time series is extensive, as overviewed by Hess and others in work published in 2001. However, not all data patterns behave in a linear fashion or, at least, a monotonous increasing or decreasing fashion. Therefore, it may be advantageous to analyse data with more flexible trends. Once flexibility is introduced the problem of detecting statistically significant increase/decrease becomes much more complicated: the trend may be alternating between being constant, decreasing or increasing. As a consequence, the problem of detecting significant increases or decreases cannot be summarised in one single figure or statistical test, as in the case of linear trend detection.Here, three functions of time are proposed so as to grasp the uncertainty in flexible trend estimates, denoted as μ t , with t=1,…,N. These functions are: (i) the actual trend estimate μ t , plus its uncertainty, (ii) the first difference in the trend μ t μ t−1, with its uncertainty and (iii) the lagged difference μ N μ t , with its uncertainty. These three functions can be argued as giving enough practical information on significance for most environmental applications. Furthermore, it is shown that these confidence limits can by estimated within the Kalman-filter framework of structural time-series models. The reason for choosing trends from this class of models is not that they are necessarily ‘better’ than other trend models but the sole presence of mathematical formulae for the uncertainty in the differences μ t μ s with 1⩽stN. The choice of a proper trend model is not trivial and is addressed in an appendix. The approach is illustrated using the software package TrendSpotter, which is available from the author.
Keywords: Integrated random walk; Kalman filter; Maximum likelihood; Structural time-series analysis; Trend; Uncertainty;

This study aims to obtain a simplified understanding of the European carbon monoxide (CO) budget, specifically focusing on the seasonal variability of sources and sinks with the help of a box-model. The information provided by such a model can be meaningful as a first order estimate for the CO budget in Europe, which is one of the main source regions of anthropogenic CO. The model allows the assessment of the incremental change in atmospheric CO concentration caused by the CO direct emission and CO chemical production in Europe. The output of the model is validated against available observational data, both in absolute terms and with respect to the seasonal variation of CO mixing ratio. Furthermore, the first order source apportionment provided by the model is compared to those retrieved from global 3D chemical-transport models (CTMs). The total incremental change caused by the European sources is estimated to be 91.4±21.1 Tg CO yr−1, while the inward advection is 52.2±13.8 Tg CO yr−1. The annual share of the primary and secondary anthropogenic sources is about 85±10% in the total. The total sink strength, including outward advection, reaction with hydroxyl radicals and dry deposition, is calculated to be 150.0±49.4 Tg CO yr−1. It should be noted that the outward advection represents 80±10% of the total sink strength.
Keywords: Carbon monoxide; Budget calculation; Box-model; Mixing ratio; Seasonal cycle; Europe;

We use data from a unique 40-year record of 150 urban and rural stations in the “Black Smoke and SO2 Network” in Great Britain to infer information about sources of atmospheric black carbon (BC). The data show a rapid decline of ambient atmospheric BC between 1962 and the early 1990s that exceeds the decline in official estimates of BC emissions based only on amount of fuel use and mostly fixed emission factors. This provides empirical confirmation of the existence and large impact of a time-dependent “technology factor” that must multiply the rate of fossil fuel use. Current ambient BC amounts in Great Britain comparable to those in western and central Europe, with diesel engines being the principal present source. From comparison of BC and SO2 data we infer that current BC emission inventories understate true emissions in the UK by about a factor of two. The results imply that there is the potential for improved technology to achieve large reduction of global ambient BC. There is a need for comparable monitoring of BC in other countries.
Keywords: Black carbon; Black smoke; Emission trends; Sources; Technology factor;

To understand the summertime variation pattern of CH4 oxidation in the rhizosphere, CH4 oxidation was evaluated in a freshwater marsh vegetated with Carex lasiocarpa and Carex meyeriana in the Sanjiang plain of northeast China at the three growing stages. Two methods through covering plants with a black cloth and applying acetylene to inhibit CH4 oxidation were used to quantify CH4 oxidation rates in the field. CH4 fluxes and CH4, dissolved organic carbon (DOC) and CO2 concentrations in porewater in the freshwater marsh were determined before and after the plants were covered or acetylene was applied. Temperature and redox potential in the vertical profile as well as aboveground and underground plant biomass were measured as well. Due to CH4 oxidation, CH4 concentrations in porewater in the C. lasiocarpa and C. meyeriana marsh were reduced by 2.1–18.2% and 0.7–25.8%, and the fluxes of potential CH4 emissions were lowered by 3.2–35.9% and 4.3–38.5%, respectively. The highest CH4 oxidation rate occurred in June, up to 30.1–38.5% of the potential CH4 fluxes, whereas the correspondent value was only 3.2–15.8% in July and August. CH4 oxidation rates in the Carex marsh decreased with increasing temperature in the vertical profile over the growing season. This is due likely to more O2 released from the roots in porewater to be consumed by other aerobic microbes in the rhizosphere at high temperature, resulting in the decrease of the CH4 oxidation rate.
Keywords: Carex marsh; Methane concentration; Methane emission; Methane oxidation; Summertime variation;

Suspended particulate matter and its relations to the urban climate in Dar es Salaam, Tanzania by P Jonsson; C Bennet; I Eliasson; E Selin Lindgren (4175-4181).
Relationships between sources and levels of particulate matter and climatic parameters (urban heat island intensity, wind speed, temperature and relative humidity) were investigated in the coastal city of Dar es Salaam, Tanzania's largest city. Measurements were made during the wet and dry seasons of 2001 at an urban and a rural site. Five elements were used to represent different sources: K in fine particles (biomass), Zn in fine particles (industry), Cl in coarse particles (sea spray), Ti in coarse particles (soil) and Pb in fine particles (traffic). The concentrations of these elements varied considerably between the urban and rural site during both the wet and dry season, with the urban site in the dry season having the highest concentrations. Diurnal differences are also apparent, although not as straightforward. In an attempt to explain these differences, correlations between all elements and the climatic parameters were investigated. The results show that the nocturnal urban heat island intensity was positively correlated and wind speed negatively correlated with particulate levels, presumably due to the increased atmospheric stability.
Keywords: Urban climate; Suspended particulate matter; Elements; Energy dispersive X-ray fluorescence; Dar es Salaam; Seasonal variations;

Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets by Linda S Johansson; Bo Leckner; Lennart Gustavsson; David Cooper; Claes Tullin; Annika Potter (4183-4195).
Emissions from commercial residential boilers fired with wood logs and wood pellets, have been compared. Seven boilers, selected with respect to age, design, connection to heat storage tank, and type of biofuel, were included in the study, which also covers two oil-fired boilers in comparison. The measurements of gaseous emissions comprised carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), total organic carbons (TOC), nitrogen oxides (NO x ), polycyclic aromatic hydrocarbons (PAH), and 33 volatile organic compounds (VOC). Particle emissions were characterised by mass concentration, number concentration, and the corresponding particle size distributions. In general, old-type wood boilers caused considerably higher emissions than modern wood and pellet boilers. The mass concentration of particles was 180 times larger in the worst old-type case (a water-cooled wood boiler without heat storage tank) compared to the best modern case (wood pellets). The TOC emission was shown to be correlated to the CO emission, both ranging between very low values and up to 10 000 mg/MJ, depending on design and operation. The highest emissions of unoxidised compounds occurred at the highest excess air ratio, and oxygen was not the limiting parameter for poor combustion. Instead, high excess air can be suspected to cool the combustion chamber, resulting in high CO emissions. VOC was dominated by methane. Especially from an old-type boiler the methane emissions could be high and the effect on climate change then may become larger than that of an oil boiler. However, substitution of an old-type wood boiler with a modern wood boiler attached to a storage tank or with a pellet boiler, would reduce methane emissions by 8 to 9000 times and the efficiency would increase. Most emissions could be considerably lowered by connecting the old-type wood boiler to a heat storage tank, or by charging small (in relation to the combustion chamber) batches of wood.
Keywords: Wood; Pellets; Domestic combustion; Emissions; Biofuel;

Trichloroacetic acid in the vegetation of polluted and remote areas of both hemispheres—Part II: salt lakes as novel sources of natural chlorohydrocarbons by Ludwig Weissflog; Nikolai Elansky; Erich Putz; Gert Krueger; Christian A Lange; Lida Lisitzina; Andrea Pfennigsdorff (4197-4204).
One of the issues provided for by the 1993 existing substances regulation (793/93/EEC) is the assessment of the environmental risk emanating from waste materials. One such material is the highly volatile substance perchloroethene (PER; TECE). PER is produced in large quantities all over the world by the chemical industry. There are many industrial processes in which PER escapes into the environment, especially the atmosphere. It has since been proven that after entering plants via the air/leaf pathway, airborne PER can be metabolised into the phytotoxic substance trichloroacetic acid. However our own studies detected relatively high levels of TCA in environmental compartments in regions far away from industry which cannot be explained by the anthropogenic input of airborne substances into the relevant ecosystems. This indicates that natural PER emittents also exist and must be identified, in order to find out more about the global spread of PER.This paper reports on the findings of related fieldwork in the Kalmykian Steppe. This area of steppe in southern Russia spans an area extending west-to-east from the Black Sea and the Caspian Sea and north-to-south between the Greater Caucasus and Volgograd. The main aim of the experiments in the Kalmykian Steppe was to study water from lakes, rivers and springs with differing levels of salinity. The concentrations of the chlorinated hydrocarbons (VCHCs) chloroform (CHCl3), tetrachloromethane (CCl4), 1,1,1-trichloroethane (1,1,1-C2H3Cl3), trichloroethene (TRI; C2HCl3), tetrachloroethene (PER; C2Cl4) and TCA in these waters were measured, along with the levels of cations and anions and the pH-value of the waters. The measurements indicate that in particular water from salt lakes located in semiarid/arid areas of the study region must be considered as new types of natural emittents of PER and other chlorinated hydrocarbons as well as trichloroacetic acid. Furthermore, attention is drawn to ecological impacts resulting from the occurrence of these substances in connection with the desertification observed in this area since the mid-20th century. Possible global associations between TCA phytotoxicity, the consumption of water by contaminated plants and the resulting impact on the regional water cycle are discussed.
Keywords: Trichloroacetic acid; Perchloroethene; Trichloroethene; Natural sources; Salt lakes;

Mercury gas exchanges over selected bare soil and flooded sites in the bay St. François wetlands (Québec, Canada) by Laurier Poissant; Martin Pilote; Philippe Constant; Conrad Beauvais; Hong H Zhang; Xiaohong Xu (4205-4214).
In order to evaluate and understand the mercury gas exchange processes in fluvial wetlands, related researches were initiated in a St. Lawrence River wetland (Bay St. François, Qué., Canada). Mercury fluxes were measured using dynamic flux chamber methods, coupled with an automatic mercury vapor analyzer (namely, Tekran, Model 2537A). Mercury air–surface gas exchanges as well as meteorological conditions were measured during two intensive field campaigns from August to September, 1999 and May, 2000, respectively. The field studies in 1999 were performed under bare soil (unvegetated portions) dry wetland conditions whereas the studies in 2000 were conducted under flooded conditions. Both field measurements were performed at the same location in the aim to study the impact of the water levels on the mercury fluxes. The water-level effect was simply to provide either a dry or a flooded site. Water-level fluctuations in fluvial wetland can result in a conversion between a standing water environment and an environment in which sediments are exposed to air. Mercury flux dynamics and processes would alter accordingly to changing environmental conditions. The average concentration of total Hg in the soil and water were ∼0.06 ng mg−1 (dry weight basis) and ∼1 ng l−1, respectively. The predominant flux of Hg° over both bare soil and water was emission. Median Hg flux under dry conditions was 0.83 ng m−2  h−1 in comparison with 0.50 ng m−2  h−1 under flooded conditions. Correlations between Hg flux, net radiation and temperature (bare soil or water) indicated that the main process involved in air–soil gas exchange under dry conditions is the enthalpy of volatilization; whereas photoreduction predominates under flooded conditions. This paper discusses the Hg flux results under both conditions in the perspective of water-level fluctuations and their impacts on the air–surface exchange of mercury.
Keywords: Mercury; Air–surface exchange; Volatilization; Deposition; Wetland;

Fog and precipitation chemistry at Delhi, North India by K Ali; G.A Momin; S Tiwari; P.D Safai; D.M Chate; P.S.P Rao (4215-4222).
Fog water samples were collected during three consecutive winters from the year 2000 to 2003 and their chemical compositions were studied to describe and assess the air quality in Delhi. It was found that all the samples were alkaline in nature in comparison to the neutrality of atmospheric CO2 equilibrated pure water. Neutralization of fog acidity by cations occurs in the order of NH4 +>Ca2+>Mg2+. Comparison of the chemical composition of fog water and that of rain water, which were collected during the same period, indicates that nearly all the chemical constituents were higher in fog water than those in rain water except for one case of rain water which occurred on 25 December 2003. On account of much less amount of rainfall on the very occasion, all the ionic species showed very high concentration. Concentration of nitrate both in fog and temporally nearest rain water samples was nearly the same except for the rain sample of 25 December 2003, which indicates that while fog water drags only the lower tropospheric NO3 , rain water collects an appreciable amount of NO3 from aloft as well. Major contribution to the total lower tropospheric NH4 + ion was made through human and animal excretion during winter season. Finally, natural source of cations like Ca2+, K+ and Mg2+ dominated over the anthropogenically produced acidic anions. Correlation analysis between different chemical species was computed, but no concrete conclusion is drawn on the basis of this result, because the data set is statistically very small. Nevertheless, it gives an idea about the source of different ions and their chemical composition.
Keywords: Neutralization; Acidity; Fog; Chemical composition;

Organic composition of aerosol particulate matter during a haze episode in Kuala Lumpur, Malaysia by M Radzi Bin Abas; Noorsaadah A Rahman; Nasr Yousef M.J Omar; M.Jamil Maah; Azizan Abu Samah; Daniel R Oros; Angelika Otto; Bernd R.T Simoneit (4223-4241).
The solvent-extractable compounds of urban airborne particulate matter were analyzed to determine the distributions of homologous and biomarker tracers. Samples were collected by high-volume air filtration during the haze episode of 1997 around the University of Malaya campus near Petaling Jaya, a suburb of Kuala Lumpur, Malaysia. These results show that the samples contain n-alkanes, n-alkan-2-ones, n-alkanols, methyl n-alkanoates, n-alkyl nitriles, n-alkanals, n-alkanoic acids, levoglucosan, PAHs, and UCM as the dominant components, with minor amounts of terpenoids, glyceryl esters and sterols, all derived from natural biogenic sources (vascular plant wax), from burning of biomass, and from anthropogenic utilization of fossil fuel products (lubricating oil, vehicle emissions, etc.). Some compositional differences are observed in the samples and greater atmospheric concentrations were found for almost all organic components in the samples collected near a roadway. The results interpreted in terms of major sources are due to local build-up of organic contaminants from vehicular emissions, smoke from biomass burning, and natural background as a result of the atmospheric stability during the haze episodes. The organic components transported in from areas outside the region, assuming all smoke components are external to the city, amount to about 30% of the total organic particle burden.
Keywords: Haze; Aliphatic components; Petroleum components; Biomarkers; Levoglucosan; PAHs;

Receptor modeling of ambient VOC at Santiago, Chile by Héctor Jorquera; Bernhard Rappenglück (4243-4263).
Ambient VOC measured at a 1996 spring campaign at Santiago, Chile, have been analyzed using the receptor models UNMIX and Positive Matrix Factorization (PMF). The ambient campaign took place at two sites: a downtown site, close to major traffic emissions, and a residential site, downwind of major industrial sources and highways. At the downtown site the following source apportionments estimates were obtained: fuel evaporation, 29.7±5.6%; gasoline exhaust, 22.0±3.4%; diesel exhaust, 18.1±2.9%; biogenic, LPG and evaporative emissions, 18.0±3.4%, unexplained: 12%. At the residential site, the following source apportionment was obtained: transported gasoline exhaust, 31.2±4.1%; local gasoline exhaust, 25.5±4.0%; evaporative losses, 11.7±2.8%; LPG losses, 11.0±2.5%; biogenic emissions, 7.7±1.7%; diesel exhaust, 6.2±1.5%; unexplained, 7.7%. Thus, near 70% of ambient VOC impacts at both sites are due to mobile sources. The receptor analyses produced source profiles that had distinctive, dominant compounds; in addition, source contributions exhibited diurnal profiles that were consistent with ambient temperature and wind speed data, and the expected activity patterns within the city. Typical errors in the source contributions vary between 15% for the larger sources—like gasoline exhaust—and 25% for the smaller sources—like biogenic emissions. It was found that the number of factors given by the UNMIX model was a good starting point to refine the solution using PMF. Both models showed good performance at discriminating between source profiles that had similar compositions in subsets of common species, but PMF was able to find better, cleaner source profiles that did UNMIX. At both monitoring sites LPG losses appear mixed in with other source profiles, and this feature could not be solved by adding more source profiles in the analyses; this was likely due to a lack of C3 measurements needed to better resolve an LPG source profile.
Keywords: Ambient VOC; Receptor models; Positive matrix factorization (PMF); UNMIX; VOC source apportionment;