Noreen D. Poor

In situ leaching investigation of pH and nitrite concentration in concrete pore solution

Abstract Holes 3- to 5-mm in diameter were drilled in concrete and mortar specimens with and without calcium nitrite corrosion inhibitor. The holes were partially filled with distilled water to leach out soluble ions from the surrounding pores. The pH in the solution inside the holes was periodically monitored with a micro-pH glass electrode and a silver-silver chloride reference electrode. A small fraction of the solution (∼10 μL) was also periodically extracted for spectrophotometric nitrite content determination. The terminal nitrite and pH values of the water in the holes matched the pore water compositions obtained in confirmatory tests using a conventional pore solution expression technique. The specimens without corrosion inhibitor yielded terminal pH ∼ 13.4. Specimens with nitrite inhibitor had pH ∼ 0.3 units lower than those without inhibitor. The terminal solution nitrite ion content was ∼8,000 ppm, which indicated that ∼10% of the total admixed nitrite was present in the pores. The pH drop was found to be quantitatively related to limited solubility of Ca(OH)2 and its precipitation upon introduction of Ca(NO2)2.

A new pseudodeterministic multivariate receptor model for individual source apportionment using highly time‐resolved ambient concentration measurements

A new multivariate pseudodeterministic receptor model (PDRM), combining mass balance and Gaussian plume dispersion equations, was developed to exploit highly time-resolved ambient measurements of SO 2 and particulate pollutants influencing air quality at a site in Sydney, Florida, during the Tampa Bay Regional Aerosol Chemistry Experiment (BRACE) in May 2002. The PDRM explicitly exploits knowledge of the number and locations of major stationary sources, source and transport wind directions, stack gas emission parameters, and meteorological plume dispersion parameters during sample collections to constrain solutions for individual sources. Model outputs include average emission rates and time-resolved ambient concentrations for each of the measured species and time-resolved meteorological dispersion factors for each of the sources. The model was applied to ambient Federal Reference Method SO 2 and 30-min elemental measurements during an 8.5-hour period when winds swept a 70° sector containing six large stationary sources. Agreement between predicted and observed ambient SO 2 concentrations was extraordinarily good: The correlation coefficient (R 2 ) was 0.97, their ratio was 1.00 ± 0.18, and predicted SO 2 emission rates for each of four large utility sources lie within 8% of their average continuous emission monitor values. Mean fractional bias, normalized mean square error, and the fractions of the predictions within a factor of 2 of the observed values are -2.7, 0.9, and 94%, respectively. For elemental markers of coal-fired (As and Se) and oil-fired (Ni) power plant emissions the average ratio of predicted and observed concentrations was 1.02 ± 0.18 for As, 0.96 ± 0.17 for Se, and 0.99 ± 0.41 for Ni, indicating that the six sources located in the wind sector between approximately 200° and 260° well accounted for background-corrected concentrations measured at the sampling site. Model results were relatively insensitive to the choice of upper bound used to constrain solutions.

NITRITE DIFFUSIVITY IN CALCIUM NITRITE-ADMIXED HARDENED CONCRETE

Abstract The apparent diffusivities ( D app ) of nitrite in concrete were estimated by monitoring time-dependent concentrations of nitrite leached into water from calcium nitrite-admixed hardened concrete specimens. Experiments were conducted with five different concrete mixes and with deionized water (DI), limewater, or synthetic seawater as the leaching agents. The D app in Type II Portland cement concrete for long curing times and a w/c ratio of 0.40 was ∼1.7×10 −8 cm 2 /s when leached at 22 °C with limewater. The D app was relatively insensitive to nitrite dosage and to DI or limewater as the leaching agent, but an increase in the w/c ratio to 0.49, or an increase in temperature by ∼14 °C, increased D app by ∼50%. A 20% Type F fly ash cement replacement reduced the apparent diffusivity by ∼60%. The D app decreased with concrete curing time. The magnitude of the D app and its dependence on concrete and exposure parameters were comparable to those observed in the transport of chloride ions in concrete.

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 (PM2.5) fraction. The average concentrations of DIN and DON in the PM2.5 fraction were 54.4 ± 25.6 nmol-Nm−3 and 6.5 ± 4.4 nmol-Nm−3, respectively.

Application of watershed deposition tool to estimate from CMAQ simulations the atmospheric deposition of nitrogen to Tampa Bay and its watershed

The U.S. Environmental Protection Agency (EPA) has developed the Watershed Deposition Tool (WDT) to calculate from the Community Multiscale Air Quality (CMAQ) model output the nitrogen, sulfur, and mercury deposition rates to watersheds and their sub-basins. The CMAQ model simulates from first principles the transport, transformation, and removal of atmospheric pollutants. We applied WDT to estimate the atmospheric deposition of reactive nitrogen (N) to Tampa Bay and its watershed. For 2002 and within the boundaries of Tampa Bays watershed, modeled atmospheric deposition rates averaged 13.3 kg N ha−1 yr−1 and ranged from 6.24 kg N ha−1 yr−1 at the bays boundary with Gulf of Mexico to 21.4 kg N ha−1 yr−1 near Tampas urban core, based on a 12-km × 12-km grid cell size. CMAQ-predicted loading rates were 1,080 metric tons N yr−1 to Tampa Bay and 8,280 metric tons N yr−1 to the land portion of its watershed. If we assume a watershed-to-bay transfer rate of 18% for indirect loading, our estimates of the 2002 direct and indirect loading rates to Tampa Bay were 1,080 metric tons N and 1,490 metric tons N, respectively, for an atmospheric loading of 2,570 metric tons N or 71% of the total N loading to Tampa Bay. To evaluate the potential impact of the U.S. EPA Clean Air Interstate Rule (CAIR, replaced with Cross-State Air Pollution Rule), Tier 2 Vehicle and Gasoline Sulfur Rules, Heavy Duty Highway Rule, and Non-Road Diesel Rule, we compared CMAQ outputs between 2020 and 2002 simulations, with only the emissions inventories changed. The CMAQ-projected change in atmospheric loading rates between these emissions inventories was 857 metric tons N to Tampa Bay, or about 24% of the 2002 loading of 3,640 metric tons N to Tampa Bay from all sources. Implications: Air quality modeling reveals that atmospheric deposition of reactive nitrogen (N) contributes a significant fraction to Tampa Bays total N loading from external sources. Regulatory drivers that lower nitrogen oxide emissions from power plants and motor vehicles are important to bay management strategies, which seek to improve water quality through N load reduction.