Investigation of the Ultraviolet Photolysis Method for the Determination of Organic Nitrogen in Aerosol Samples

Abstract

The research objective was to adapt the ultraviolet (UV)photolysis method to determine dissolved organic nitrogen (DON) in aqueous extracts of aerosol samples. DON was assumed to be the difference in total concentration of inorganic nitrogen forms before and after sample irradiation. Using a 2² factorial design the authors found that the optimal conversion of urea, amino acids (alanine, aspartic acid, glycine, and serine), and methylamine for a reactor temperature of 44 °C occurred at pH 2.0 with a 24-hr irradiance period at concentrations < µM of organic nitrogen. Different decomposition mechanisms were evident: the photolysis of amino acids and methylamine released mainly ammonium (NH₄ ⁺), but urea released a near equimolar ratio of NH₄ ⁺ and nitrate (NO₃ ^?). The method was applied to measure DON in the extracts of aerosol samples from Tampa, FL, over a 32-day sampling period. Average dissolved inorganic (DIN) and DON concentrations in the particulate matter fraction PM₁₀ were 78.1 ± 29.2 nmol-Nm^?3and 8.3 ± 4.9 nmol-Nm^?3, respectively. The ratio between DON and total dissolved nitrogen ([TDN] = DIN + DON) was 10.1 ± 5.7%, and the majority of the DON (79.1 ± 18.2%) was found in the fine particulate matter (PM_2.5) fraction. The average concentrations of DIN and DON in the PM_2.5 fraction were 54.4 ± 25.6 nmol-Nm^?3 and 6.5 ± 4.4 nmol-Nm^?3, respectively.     

Aerosol Filtration by Sorbent Beds

Fixed beds of sorbent media are used for the evaluation of poiynuclear aromatic hydrocarbons (PAH) present in air. Twostage sampling and separate extraction and analyses of PAH associated with aerosol particles and those present in the vapor state are usually performed. The ability of commonly used sorbents to retain particulate matter introduces a potential for reducing the time and cost of PAH evaluation procedures.

The filtration efficiency of three sorbent media, Florisil, XAD-2, and polyurethanefoam (PUF), for particles in 0.1 to 1 µm size range was studied using airflow rates from 4 to 2501 /mm through a PS 1 sorbent cartridge. Theoretical considerations were used to identify the principal filtration mechanisms and to assess the predictability of the aerosol filtration performance of sorbent filters. The results of this study indicate XAD-2 to be an efficient filtration medium owing to the electrostatic enhancement of capturing and retaining aerosol particles.

As a result of theoretical considerations, Brownian diffusion and inertial deposition were found to be major filtration mechanisms accompanied by electrostatic effects. While the efficiency of the diffusional deposition mechanism was reasonably well predicted with available theories, modeling of submicron particle impaction at higher fluid velocities appeared to be inadequate. Further developments are suggested to improve our understanding of filtration phenomena in sorbent beds under high flow rate conditions.     

A History of the Production and Use of Carbon Tetrachloride,Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 1--Historical Background; Carbon Tetrachloride and Tetrachloroethylene

Carbon tetrachloride (CTC), tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) were four of the most widely used cleaning and degreasing solvents in the United States. These compounds were also used in a wide variety of other applications. The history of the production and use of these four compounds is linked to the development and growth of the United States' synthetic organic chemical industry, and historical events that affected the development and use of chlorinated solvents in general. Part 1 of this article includes a discussion of the historical background common to each of the four solvents, followed by discussion on the history of CTC and PCE. In the early years of the 20th century, CTC became the first of the four solvents to come into widespread use. CTC was used as a replacement for petroleum distillates in the dry-cleaning industry, but was later replaced by PCE. In the 1990s, CTC was phased out under the Montreal Protocol due to its role in stratospheric ozone depletion.     

Estimating the Cumulative Ecological Effect of Local Scale Landscape Changes in South Florida

Ecosystem restoration in south Florida is a state and national priority centered on the Everglades wetlands. However, urban development pressures affect the restoration potential and remaining habitat functions of the natural undeveloped areas. Land use (LU) planning often focuses at the local level, but a better understanding of the cumulative effects of small projects at the landscape level is needed to support ecosystem restoration and preservation. The South Florida Ecosystem Portfolio Model (SFL EPM) is a regional LU planning tool developed to help stakeholders visualize LU scenario evaluation and improve communication about regional effects of LU decisions. One component of the SFL EPM is ecological value (EV), which is evaluated through modeled ecological criteria related to ecosystem services using metrics for (1) biodiversity potential, (2) threatened and endangered species, (3) rare and unique habitats, (4) landscape pattern and fragmentation, (5) water quality buffer potential, and (6) ecological restoration potential. In this article, we demonstrate the calculation of EV using two case studies: (1) assessing altered EV in the Biscayne Gateway area by comparing 2004 LU to potential LU in 2025 and 2050, and (2) the cumulative impact of adding limestone mines south of Miami. Our analyses spatially convey changing regional EV resulting from conversion of local natural and agricultural areas to urban, industrial, or extractive use. Different simulated local LU scenarios may result in different alterations in calculated regional EV. These case studies demonstrate methods that may facilitate evaluation of potential future LU patterns and incorporate EV into decision making.     

Nutrient removal in tropical subsurface flow constructed wetlands under batch and continuous flow conditions

The aim of this investigation was to evaluate the influence of batch versus continuous flow on the removal efficiencies of chemical oxygen demand (COD), nitrogen (N) and total phosphorus (TP) in tropical subsurface flow constructed wetlands (SSF CW). The quantitative role of the higher aquatic plants in nutrient removal in these two operational modes was also investigated. Results indicated no significant difference (p > 0.05) in COD removal between batch and continuous flow modes for either the planted or unplanted treatments. Furthermore, the batch-loaded planted wetlands showed significantly (p < 0.05) higher ammonium removal efficiencies (95.2%) compared with the continuously fed systems (80.4%), most probably because the drain and fill batch mode presented systematically more oxidized environmental conditions. With respect to TP removal, for both planted and unplanted beds, there was significant enhancement (p < 0.05) in batch flow operation (69.6% for planted beds; 39.1% for unplanted beds) as compared to continuous flow operation (46.8% for planted beds; 25.5% for unplanted beds). In addition, at a 4-day hydraulic retention time (HRT), the presence of plants significantly enhanced both ammonia oxidation and TP removal in both batch and continuous modes of operation as compared to that for unplanted beds. An estimation of the quantitative role of aeration from drain and fill operation at a 4-day HRT, as compared to rhizosphere aeration by the higher aquatic plant, indicated that drain and fill operation might account for only less than half of the higher aquatic plant's quantitative contribution of oxygen (1.55 g O2 per m2 per day for batch flow versus 1.13 g O2 per m2 per day for continuous flow).     

Rubber and pulp plantations represent a double threat to Hainan's natural tropical forests

Hainan, the largest tropical island in China, belongs to the Indo-Burma biodiversity hotspot and harbors large areas of tropical forests, particularly in the uplands. The Changhua watershed is the cradle of Hainan's main river and a center of endemism for plants and birds. The watershed contains great habitat diversity and is an important conservation area. We analyzed the impact of rubber and pulp plantations on the distribution and area of tropical forest in the watershed, using remote sensing analysis of Landsat images from 1988, 1995 and 2005. From 1988 to 1995, natural forest increased in area (979-1040?sq?km) but decreased rapidly (763?sq?km) over the next decade. Rubber plantations increased steadily through the study period while pulp plantations appeared after 1995 but occupied 152?sq?km by 2005. Rubber and pulp plantations displace different types of natural forest and do not replace one another. Because pulp is not as profitable as rubber and existing pulp processing capacity greatly exceeds local supply, considerable pressure exists on remaining upland forests. We recommend for future management that these plantation forests be reclassified as 'industrial', making a clear policy distinction between natural and industrial forestry. Additionally, the local government should work to enforce existing laws preventing forest conversion on marginal and protected areas.     

Simulating Land-Cover Change in Montane Mainland Southeast Asia

We used the conversion of land use and its effects (CLUE-s) model to simulate scenarios of land-cover change in Montane mainland southeast Asia (MMSEA), a region in the midst of transformation due to rapid intensification of agriculture and expansion of regional trade markets. Simulated changes affected approximately 10 % of the MMSEA landscape between 2001 and 2025 and 16 % between 2001 and 2050. Roughly 9 % of the current vegetation, which consists of native species of trees, shrubs, and grasses, is projected to be replaced by tree plantations, tea, and other evergreen shrubs during the 50 years period. Importantly, 4 % of this transition is expected to be due to the expansion of rubber (Hevea brasiliensis), a tree plantation crop that may have important implications for local-to-regional scale hydrology because of its potentially high water consumption in the dry season.     

Reforestation Strategies Amid Social Instability: Lessons from Afghanistan

Foreign and domestic government agencies and other international organizations pursue reforestation programs in rural upper watershed areas of Afghanistan over the past decade to alleviate poverty, combat the insurgency and rehabilitate a depleted forest resource base. Popular programs incorporate cash-for-work to conduct hillside terracing, check dam construction and tree-planting for nut production, fuel wood, timber, dune stabilization, and erosion abatement. Programmatic approaches have varied as a function of accessibility, security and local objectives. Uncertain land tenure and use rights, weak local environmental management capacity, and a focus on agricultural production to meet immediate needs limit interest, nationally and locally. Unreliable security, a lack of high quality tree planting stock, limited technical knowledge and coordination among government agencies, and poor security hamper program expansion. Reforestation success would be most likely where these issues are least acute. The Afghan government should focus on supporting community based natural resource management, developing and disseminating improved conservation tree nursery strategies, and promoting watershed management schemes that incorporate forestry, range management and agronomic production. Reforestation practitioners could benefit from the human and material resources now present as part of the international war effort. Successes and failures encountered in Afghanistan should be considered in order to address similar problems in insecure regions elsewhere when reforestation may help reverse environmental degradation and contribute to broader social stabilization efforts.     

Investigation of an Escherichia coli environmental benchmark for waterborne pathogens in agricultural watersheds in Canada

Canada's National Agri-Environmental Standards Initiative sought to develop an environmental benchmark for low-level waterborne pathogen occurrence in agricultural watersheds. A field study collected 902 water samples from 27 sites in four intensive agricultural watersheds across Canada from 2005 to 2007. Four of the sites were selected as reference sites away from livestock and human fecal pollution sources in each watershed. Water samples were analyzed for Campylobacter spp., Salmonella spp., Escherichia coli O157:H7, Cryptosporidium spp., Giardia spp., and the water quality indicator E. coli. The annual mean number of pathogen species was higher at agricultural sites (1.54 ± 0.07 species per water sample) than at reference sites (0.75 ± 0.14 species per water sample). The annual mean concentration of E. coli was also higher at agricultural sites (491 ± 96 colony-forming units [cfu] 100 mL(-1)) than at reference sites (53 ± 18 cfu 100 mL(-1)). The feasibility of adopting existing E. coli water quality guideline values as an environmental benchmark was assessed, but waterborne pathogens were detected at agricultural sites in 80% of water samples with low E. coli concentrations (<100 cfu 100 mL(-1)). Instead, an approach was developed based on using the natural background occurrence of pathogens at reference sites in agricultural watersheds to derive provisional environmental benchmarks for pathogens at agricultural sites. The environmental benchmarks that were derived were found to represent E. coli values lower than geometric mean values typically found in recreational water quality guidelines. Additional research is needed to investigate environmental benchmarks for waterborne pathogens within the context of the "One World, One Health" perspective for protecting human, domestic animal, and wildlife health.