Condensed atmospheric photooxidation mechanisms for isoprene

Two condensed mechanisms for the atmospheric reactions of isoprene, which differ in the number of species used to represent isoprene's reactive products, have been developed for use in ambient air quality modehng. They are based on a detailed isoprene mechanism that has recently been developed and extensively evaluated against environmental chamber data. The new condensed mechanisms give very close predictions to those of the detailed mechanism for ozone, OH radicals, nitric acid, H₂O₂, formaldehyde, total PANS, and for incremental effects of isoprene on ozone formation in one day simulations. The effects of the condensations become somewhat greater in multi-day simulations, particularly in cases where NO₃ reactions are important at nighttime, but the ozone predictions are still very close. On the other hand, the SAPRC-90, RADM-2, and Carbon Bond IV isoprene mechanisms give quite different predictions of these quantities. It is recommended that the new mechanisms replace those currently used in airshed simulations where isoprene emissions are important.     

Effects of Wind Direction on Coarse and Fine Particulate Matter Concentrations in Southeast Kansas

Abstract

Field data for coarse particulate matter ([PM] PM₁₀) and fine particulate matter (PM_2.5) were collected at selected sites in Southeast Kansas from March 1999 to October 2000, using portable MiniVol particulate samplers. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste in the area located in the communities of Chanute, Independence, Fredonia, and Coffeyville. Both spatial and temporal variation were observed in the data. Variation because of sampling site was found to be statistically significant for PM₁₀ but not for PM_2.5. PM₁₀ concentrations were typically slightly higher at sites located within the four study communities than at background sites. Sampling sites were located north and south of the four targeted sources to provide upwind and downwind monitoring pairs. No statistically significant differences were found between upwind and downwind samples for either PM₁₀ or PM_2.5, indicating that the targeted sources did not contribute significantly to PM concentrations. Wind direction can frequently contribute to temporal variation in air pollutant concentrations and was investigated in this study. Sampling days were divided into four classifications: predominantly south winds, predominantly north winds, calm/variable winds, and winds from other directions. The effect of wind direction was found to be statistically significant for both PM₁₀ and PM_2.5. For both size ranges, PM concentrations were typically highest on days with predominantly south winds; days with calm/variable winds generally produced higher concentrations than did those with predominantly north winds or those with winds from “other” directions. The significant effect of wind direction suggests that regional sources may exert a large influence on PM concentrations in the area.     

Development of a database for chemical mechanism assignments for volatile organic emissions

The development of a database for making model species assignments when preparing total organic gas (TOG) emissions input for atmospheric models is described. This database currently has assignments of model species for 12 different gas-phase chemical mechanisms for over 1700 chemical compounds and covers over 3000 chemical categories used in five different anthropogenic TOG profile databases or output by two different biogenic emissions models. This involved developing a unified chemical classification system, assigning compounds to mixtures, assigning model species for the mechanisms to the compounds, and making assignments for unknown, unassigned, and nonvolatile mass. The comprehensiveness of the assignments, the contributions of various types of speciation categories to current profile and total emissions data, inconsistencies with existing undocumented model species assignments, and remaining speciation issues and areas of needed work are also discussed. The use of the system to prepare input for SMOKE, the Speciation Tool, and for biogenic models is described in the supplementary materials. The database, associated programs and files, and a users manual are available online at http://www.cert.ucr.edu/~carter/emitdb.

Implications: Assigning air quality model species to the hundreds of emitted chemicals is a necessary link between emissions data and modeling effects of emissions on air quality. This is not easy and makes it difficult to implement new and more chemically detailed mechanisms in models. If done incorrectly, it is similar to errors in emissions speciation or the chemical mechanism used. Nevertheless, making such assignments is often an afterthought in chemical mechanism development and emissions processing, and existing assignments are usually undocumented and have errors and inconsistencies. This work is designed to address some of these problems.     

Fog Chemistry at an Urban Midwestern Site

This work investigates the oxidative aging of preformed secondary organic aerosol (SOA) derived from α-pinene ozonolysis (～100 ppb_v hydrocarbon [HC_x] with excess of O₃) within the University of California–Riverside Center for Environmental Research and Technology environmental chamber that occurs after introduction of additional hydroxyl (OH) and nitrate (NO₃) radicals. Simultaneous measurements of SOA volume concentration, hygroscopicity, particle density, and elemental chemical composition (C:O:H) reveal increased particle wall-loss-corrected SOA formation (1.5%, 7.5%, and 15.1%), increase in oxygen-to-carbon ratio (O/C; 15.6%, 8.7%, and 8.7%), and hydrophilicity (4.2%, 7.4%, and 1.4%) after addition of NO (ultraviolet [UV] on), H₂O₂ (UV on), and N₂O₅ (dark), respectively. The processing observed as an increase in O/C and hydrophilicity is attributed to OH and NO₃ reactions with first-generation vapor products and UV photolysis. The rate of increase in O/C appears to be only sufficient to achieve semivolatile oxygenated organic aerosol (SV-OOA) on a day time scale even at the raised chamber radical concentrations. The additional processing with UV irradiation without addition of NO, H₂O₂, or N₂O₅ is observed, adding 5.5% wall-loss-corrected volume. The photolysis-only processing is attributed to additional OH generated from photolysis of the nitrous acid (HONO) offgasing from chamber walls. This finding indicates that OH and NO₃ radicals can further alter the chemical composition of SOA from α-pinene ozonolysis, which is proved to consist of first-generation products.

Implications: Secondary organic aerosol (SOA) may undergo aging processes once formed in the atmosphere, thereby altering the physicochemical and toxic properties of aerosol. This study discusses SOA aging of a major biogenic volatile organic compound (VOC; α-pinene) after it initially forms SOA. Aging of the α-pinene ozonolysis system by OH (through NO or H₂O₂ injection), NO₃ (through N₂O₅ injection), and photolysis is observed. Although the reaction rate appears to be only sufficient to achieve semivolatile oxygenated organic aerosol (SV-OOA) level of oxygenation on a 1-day scale, it is important that SOA aging be considered in ambient air quality models. Aging in this study is attributed to further oxidation of gas-phase oxidation products of α-pinene ozonolysis.

Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air &; Waste Management Association for information on the referenced α-pinene ozonolysis reaction and chamber reactor temperature.     

Towards the characterisation of heavy metals in dredged canal sediments and an appreciation of 'availability': two examples from the UK.

Canal sediments can act as sinks for a wide range of contaminants including heavy metals from various sources (e.g. industrial and waste water discharges). Dredging of canals is required to maintain navigational depth and prevent flooding. The sediments removed from canals are often disposed of to land, being deposited either straight on to the banks of the canal or, in recent years, in licensed disposal sites. The aim of this work was to investigate the nature of dredged sediment-derived soils and the heavy metals present in them. Two disposal sites in the United Kingdom (UK) were investigated and soil samples taken. A variety of analytical techniques were used, including Aqua regia digestion and sequential extraction, in order to assess the concentrations and associations of metals present. Diethylene triaminepenta-acetic acid extracts, performed to illustrate plant-available metal concentrations, reveal that up to 40% of the total extracted metals were in an 'available' form. Variations in metal concentrations with depth in the soil cores show a significant correlation with total organic carbon content.     

Tree Structure and Diversity in Human-Impacted Littoral Forests, Madagascar

This research surveyed human-impacted littoral forests in southeastern Madagascar to determine (i) how forest structural features, indicative of human impact, are related to total, utilitarian, and endemic tree diversity; (ii) the distribution, abundance, and demographics of tree species groups (i.e., total, useful, endemic) across the landscape; and (iii) the amount of basal area available per human use category. We also use these data to consider issues of sustainable use and how human impact may influence littoral forest tree community composition across the landscape. Within 22 transects of 400 m² each, we recorded a total of 135 tree species and 2155 individuals. Seventy-nine species (58%) were utilitarian and 56 (42%) were nonutilitarian species. Of the 2155 individuals, 1827 (84%) trees were utilitarian species. We recorded 23 endemic species (17% of the total species) and 17 (74%) of these were utilitarian species. Basal area was significantly correlated with Shannon Weiner Index values for total (r = 0.64, P < 0.01), utilitarian (r = 0.58, P < 0.01), and endemic tree diversity (r = 0.85, P < 0.01). Basal area was significantly correlated with the Simpson’s index values for the endemic species (r = 0.74, P < 0.01). These correlations suggest that endemic tree species, of high global conservation value, may be the species group most influenced by changes in forest structure. Utilitarian species constituted 84% of the total basal area. The use category contributing the highest amount of basal area to the landscape was firewood. The results presented herein demonstrate that the landscape of southeastern Madagascar, commonly perceived as degraded, retains high value for both global conservation purposes and for local livelihoods. Thus, valuable opportunities may exist for developing conservation incentives that leverage both global and local conservation needs.     

Power and Sample Size Calculations for Linear Hypotheses Associated with Mixtures of Many Components using Fixed-Ratio Ray Designs

Response surface methodology, often supported by factorial designs, is the classical experimental approach that is widely accepted for detecting and characterizing interactions among chemicals in a mixture. In an effort to reduce the experimental effort as the number of compounds under study is increased, ray designs have been proposed to study combinations of chemicals. When interest is restricted to relevant mixing ratios, we are only interested in making inference along the specific rays of interest, as opposed to methods which use designs that require more experimental effort to support the estimation of a response surface over a broader experimental region. Methods have been developed for the test of additivity along multiple fixed-ratio rays. Of primary importance is the detection of interactions with reasonable power. The objective of this paper is to address power and sample size issues related to the hypothesis of no interaction.     

Complex patterns of population structure and recruitment of <Emphasis Type="Italic">Plectropomus leopardus</Emphasis> (Pisces: Epinephelidae) in the Indo-West Pacific: implications for fisheries management

Here the population genetic structure of an ecologically and economically important coral reef fish, the coral trout Plectropomus leopardus, is investigated in the context of contemporary and historical events. Coral trout were sampled from four regions (six locations) and partial mtDNA D-loop sequences identified six populations (Fst = 0.89209, P < 0.0001): Scott Reef and the Abrolhos Islands in west Australia; the Great Barrier Reef (GBR), represented by northern and southern GBR samples; New Caledonia and Taiwan, with Taiwan containing two genetic lineages. Furthermore, this study identified source and sink populations within and among regions. Specifically, the northern population in west Australia (Scott Reef) was identified, as the source for replenishment of the Abrolhos population, whilst New Caledonia was a source for recruitment to the GBR. Based on these insights from a single mtDNA marker, this study will facilitate the development of rational management plans for the conservation of P. leopardus populations and therefore mitigate the risk of population declines from anthropogenic influences.     

Improving Technical Information Use: What Can Be Learnt from a Manager’s Perspective?

Conservation practice reportedly suffers from low use of technical information. Understanding of factors that affect the influence of technical information on management decision-making is limited. We sought to identify leverage points for improved technical information dissemination in the New South Wales Parks and Wildlife Service, Australia, given the significant recent investments in monitoring and evaluation that had been made. We did so by exploring the inter-relationships between factors affecting the influence of different information types on management decisions. Results indicate that managers have a high inclination toward adaptive behavior, given they operate in an information poor environment. The most influential types of information were those that enabled interaction between information provider and recipient (e.g., staff experience and expertise). An analysis of the concordance in individuals’ responses for different information types showed that neither accessibility nor organizational expectation of use was aligned with influence on decision-making. Alignment of responses also varied by work area. Raising expectations of information use or increasing access to particular types of information is therefore unlikely to result in an increase in influence on management decision-making. Rather than focussing on matching accessibility and expected use of particular information types, our results indicate that technical information uptake is best supported through existing peer networks tailored to specific work areas.