Abundance and sources of hydrophilic and hydrophobic water-soluble organic carbon at an urban site in Korea in summer

In this study, the characteristics of total water-soluble organic carbon (WSOC) and isolated WSOC fractions were examined to gain a better understanding of the pathway of organic aerosol production. 24 h PM(2.5) samples were collected during the summer (July 28-August 28, 2009) at an urban site in Korea. A glass column filled with XAD7HP resin was used to separate the filtered extracts into hydrophilic (WSOC(HPI)) and hydrophobic (WSOC(HPO)) fractions. The origins of air mass pathways arriving at the sampling site were mostly classified into three types, those originating over the East Sea of Korea that passed over the eastern inland urban and industrial regions (type I); those from the marine (western/southwestern/southern marine) and passed over the national industrial complex regions (type II); and those from northeastern China that passed through North Korea and metropolitan areas of South Korea (type III). Measurements showed an increase in the average WSOC fraction of total OC from the type II to III air mass (53 to 64%) periods. Also, higher SO(4)(2-)/SO(x) (=SO(2) + SO(4)(2-)) was observed in the type III air mass (0.70) than those in the types I (0.49) and II (0.43). According to the average values of WSOC/OC and SO(4)(2-)/SO(x), measurements suggest that the aerosols collected during the type III air mass period were more aged or photo-chemically processed than those during the types I and II air mass periods. The relationship between the SO(4)(2-)/SO(x) and WSOC/OC (R(2) = 0.64) suggests that a significant fraction of the observed WSOC at the site could be formed by an oxidation process similar to SO(4)(2-) aerosols, probably the oxidation process using OH radicals, or in-cloud processing. The photochemical production of WSOC(HPO) was also observed to significantly contribute to the total OC.     

Catalytic upgrading pyrolysis of pine sawdust for bio-oil with metal oxides

The catalytic upgrading pyrolysis of pine sawdust was performed at 500 °C with various metal oxides to improve the quality of the bio-oil. The aim of this study was to investigate the potential of the metal oxides instead of traditional zeolites for catalytic upgrading pyrolysis with the analysis of Gas Chromatograph/Mass Spectrometer. In this study, the used catalysts were Calcium-oxide, Magnesium oxide, Titanium dioxide, and Zeolite (Si/Al?=?80). The influence of catalysts on products yields and compositions were investigated. Most metal oxides can enhance the bio-gas with the bio-oil yields decreased. The metal oxides led to a decrease of Acids, Aldehydes, Ketones and an increase of Furfural, Cresols, Catechols in Furans and Phenolics. Among the catalysts, the MgO catalysts was the most effective to convert the high molecular into lights ones (6.65% Cresols) with yield of 20.48% for Furfural. The deoxygenation reaction in bio-oil was suggested to convert oxygenated compounds into the low molecular weight of the materials (6.39% Guaiacols). Thus, the used metal oxides can improve the quality of bio-oil by decreasing undesirable compounds as well as increasing the desirable compounds with low oxygen contents via deoxygenation reaction.     

Gasification characteristics of biomass for tar removal by secondary oxidant injection

Gasification experiments for sawdust were conducted using a fixed bed reactor at 900 °C by varying the secondary oxidant injection ratio to determine the optimal conditions for tar removal along with the enhancement of gasification efficiency. Secondary oxidant was injected as an oxidant at the top zone of the gasifier in varying ratios of 10–30% of the total amount of oxidant. This method was based on the primary method of tar removal and gasification efficiency improvement by thermal cracking of tar. Various gasification performance parameters were evaluated and tar content was estimated by measuring the fluctuation of weight of the activated carbon filter. The results showed that the concentration of tar in the producer gas decreased by injecting the secondary oxidant, even though syngas yield decreased. The recycling potential of the char produced in the gasification experiments was also assessed with the purpose of utilizing char as an adsorbent by determining its surface area and pore volume. The results demonstrated that the char produced from the gasification experiment had similar quality to that of the activated carbon used in this experiment.     

Numerical study of heat transfer characteristics of char from waste tire pyrolysis

To investigate heat transfer of char from waste tire pyrolysis, the cooling of char was simulated by the computational fluid dynamics. To scrutinize the heat transfer characteristics, bed height, temperature of cooling wall, and mixing time were selected as calculation parameters. From the results, increasing the char bed height from 0.005 to 0.02 m, the total heat transfer is decreased as from 45.5 to 26.5 J. As the char bed height is further increased from 0.02 to 0.06 m, the total heat transfer is decreased from 26.5 to 9.1 J. The char bed height affects the total heat transfer significantly. The total heat transfer decreases from 15.9 to 14.0 J as the temperature of cooling wall increases from 273.15 to 323.15 K. The total heat transfer mildly depends on the temperature of cooling wall. The particle mixing time increases from 10 to 120 s and the total heat transfer decreases from 28.6 to 22.6 J. It is noted that the particle contact is enhanced between char particles as well as the particles and cooling wall as the particle mixing time decreases. Consequently, heat transfer is augmented.     

Optimization of Carbon Dioxide and Valeric Acid Utilization for Polyhydroxyalkanoates Synthesis by Cupriavidus necator

The utilization of captured CO₂ as a part of the CO₂ capture and storage system to produce biopolymers could address current environmental issues such as global warming and depletion of resources. In this study, the effect of feeding strategies of CO₂ and valeric acid on cell growth and synthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] in Cupriavidus necator was investigated to determine the optimal conditions for microbial growth and biopolymer accumulation. Among the studied CO₂ concentrations (1–20 %), microbial growth and poly(3-hydroxybutyrate) accumulation were optimal at 1 % CO₂ using a gas mixture at H₂:O₂:N₂ = 7:1:91 % (v/v). When valeric acid was fed together with 1 % CO₂, (R)-3-hydroxyvalerate synthesis increased with increasing valeric acid concentration up to 0.1 %, but (R)-3-hydroxybutyrate synthesis was inhibited at >0.05 % valeric acid. Sequential addition of valeric acid (0.05 % at Day 0 followed by 0.025 % at Day 2) showed an increase in 3HV fraction without inhibitory effects on 3HB synthesis during 4 d accumulation period. The resulting P(3HB-co-3HV) with 17–32 mol  % of 3HV is likely to be biocompatible. The optimal concentrations and feeding strategies of CO₂ and valeric acid determined in this study for microbial P(3HB-co-3HV) synthesis can be used to produce biocompatible P(3HB-co-3HV).     

Overflow risk analysis for designing a nonpoint sources control detention

This paper presents a design method by which the overflow risk related to a detention for managing nonpoint pollutant sources in urban areas can be evaluated. The overall overflow risk of a nonpoint pollutant sources control detention can be estimated by inherent overflow risk and operational overflow risk. For the purpose of calculating overflow risk, the 3-parameter mixed exponential distribution is applied to describe the probability distribution of rainfall event depth. As a rainfall-runoff calculation procedure required for deriving a rainfall capture curve, the U.S. Natural Resources Conservation Service runoff curve number method is applied to consider the nonlinearity of the rainfall-runoff relation. Finally, the detention overflow risk is assessed with respect to the detention design capacity and drainage time. The proposed overflow risk assessment is expected to provide a baseline to determine quantitative parameters in designing a nonpoint sources control detention.     

A contribution of brown carbon aerosol to the aerosol light absorption and its radiative forcing in East Asia

Brown carbon aerosols were recently found to be ubiquitous and effectively absorb solar radiation. We use a 3-D global chemical transport model (GEOS-Chem) together with aircraft and ground based observations from the TRACE-P and the ACE-Asia campaigns to examine the contribution of brown carbon aerosol to the aerosol light absorption and its climatic implication over East Asia in spring 2001. We estimated brown carbon aerosol concentrations in the model using the mass ratio of brown carbon to black carbon (BC) aerosols based on measurements in China and Europe. The comparison of simulated versus observed aerosol light absorption showed that the model accounting for brown carbon aerosol resulted in a better agreement with the observations in East Asian-Pacific outflow. We then used the model results to compute the radiative forcing of brown carbon, which amounts up to ?2.4 W m^?2 and 0.24 W m^?2 at the surface and at the top of the atmosphere (TOA), respectively, over East Asia. Mean radiative forcing of brown carbon aerosol is ?0.43 W m^?2 and 0.05 W m^?2 at the surface and at the TOA, accounting for about 15% of total radiative forcing (?2.2 W m^?2 and 0.33 W m^?2) by absorbing aerosols (BC + brown carbon aerosol), having a significant climatic implication in East Asia.     

Flux measurements of volatile organic compounds by the relaxed eddy accumulation method combined with a GC-FID system in urban Houston,Texas

A tall tower flux measurement setup was established in metropolitan Houston, Texas, to measure trace gas fluxes from emission sources in the urban surface layer. We describe a new relaxed eddy accumulation (REA) system combined with a dual-channel GC-FID used for VOC flux measurements, focusing on benzene, toluene, ethylbenzene and xylenes (BTEX) results. Ambient air sampled from 60 m above the ground next to a sonic anemometer was subsampled by a membrane pump and pushed into an REA valve system with two Teflon bag reservoirs, then transferred to two preconcentration units for thermal desorption. We discuss the performance of our system and the selected BTEX measurement results using approximately 8 weeks of data (May 22–July 22, 2008), presenting diurnal variations of concentrations and fluxes of these traffic tracers. The measured values exhibited diurnal cycles with dominant morning and midday peaks during weekdays related to rush hour traffic and additional weekday daytime toluene and xylenes emissions. Local evaporative emissions, likely from solvent usage, significantly contributed to the measured fluxes. We upscaled measured emissions to the county level using a high resolution land cover data set and compared the results with EPA’s National Emission Inventory (NEI).