The high-energy requirements of cleanrooms are the main motivation for optimizing their operational conditions. The ventilation system consumes the most energy in order to ensure the precise air conditioning of the room (filtration, temperature, and humidity adjustment). The main function of the ventilation system is to keep particle concentration to a minimum. This work deals with the optimization of an experimental operating room via the optimization of air supply through the distribution element (laminar airflow ceiling) in the range of 0.15–0.25 m·s⁻¹. The laminar airflow between the distribution element and the patient is influenced by the operating light and different airflow velocities. These factors affect changes in particle concentration. Ansys Fluent software was used to investigate the nature of the flow, velocity profiles, and particle trajectories. The results of our numerical simulation demonstrate that a suitable flow rate setting increases the efficiency of particle reduction in the operating table area by up to 54%, which can, in turn, reduce operating costs. The simulated air velocity profile was subsequently verified using the particle image velocimetry (PIV) method. The typical size of particles monitored for in cleanrooms is 0.5 μm according to ISO EN 7. Therefore, the results of this study should be helpful in correctly designing distribution elements for clean rooms. Full article

This study investigates the impact of industrial complexes on the air quality in the Ulsan Metropolitan City, Korea, by analyzing the concentration of trace substances. Importantly, this study performs segmentation and analysis of the components of particulate matter for tracking emission sources. Concentrations of particulate matter with aerodynamic diameters ≤10 and ≤2.5 µm (PM10 and PM2.5, respectively) and 19 substances comprising PM2.5 (such as ions, carbon, and nine elements) were measured hourly during the year 2017 in the southeastern intensive air quality monitoring station of the National Institute of Environmental Research, Korea. This study identified and investigated the time periods during which the vanadium content in PM2.5 was higher than the annual mean (1.026 ng/µg) through selection cases (SCs). The annual mean concentrations of PM2.5 and PM10 were 18.50 and 32.35 µg/m³, respectively, and were higher (i.e., 26.54 and 45.84 µg/m³, respectively) in SCs. Notably, the concentrations were high even when the main wind direction of SCs was southeasterly, which was mainly the case in summer. Furthermore, the emission sources contributing to PM2.5 were estimated using the correlations of organic carbon, elemental carbon, zinc, iron, manganese, and titanium concentrations in the SCs. This study demonstrated that a detailed tracking of the emission sources at a local scale is possible by analyzing the composition of the components of PM2.5. Full article

We demonstrated the relationships between elemental carbon (EC) and EC fractions during evolved gas analysis (EGA) for PM_2.5 sampled at KOREATECH from 29 March 2018 to 12 May 2018. The EC concentrations were compared to the concentrations of equivalent black carbon to confirm that the level of EC concentrations analyzed in this study was valid. Among various EC fractions and their combination, EC1+EC3 fractions were best correlated with the EC concentrations. Especially, dominant EC fraction was related with the dependence of carbon oxidation quantity on the oxidation temperature. We also examined the relationships between pyrolytic carbon (PyC) and EC concentration with respect to the split time. PyC was correlated with the split time in the phase of oxygen-helium mixture. PyC was close to zero for the split time in the helium phase. It is novel, as far as the authors know, that the correlation between PyC and the split time under NIOSH 5040 protocol was reported with regard to EGA. We believe that our study helps to identify what causes uncertainty in the quantification of PyC. Full article

In this study, more accurate information on the levels of aerosol optical depth (AOD) was calculated from the assimilation of the modeled AOD based on the optimal interpolation method. Additionally, more realistic levels of surface particulate matters over the Arctic were estimated using the assimilated AOD based on the linear relationship between the particulate matters and AODs. In comparison to the MODIS observation, the assimilated AOD was much improved compared with the modeled AOD (e.g., increase in correlation coefficients from −0.15–0.26 to 0.17–0.76 over the Arctic). The newly inferred monthly averages of PM₁₀ and PM_2.5 for April–September 2008 were 2.18–3.70 μg m⁻³ and 0.85–1.68 μg m⁻³ over the Arctic, respectively. These corresponded to an increase of 140–180%, compared with the modeled PMs. In comparison to in-situ observation, the inferred PMs showed better performances than those from the simulations, particularly at Hyytiala station. Therefore, combining the model simulation and data assimilation provided more accurate concentrations of AOD, PM₁₀, and PM_2.5 than those only calculated from the model simulations. Full article

Existing studies suggest various potential daytime sources of atmospheric nitrous acid (HONO), including photolysis surface reactions and photo-enhanced NO₂ conversion on organic surfaces. However, the understanding of daytime HONO sources is still inadequate. In this study, we report the HONO formation on asphalt surfaces under various NO₂, VOCs (toluene and hexane), and UV irradiance conditions using a continuous flow chamber. Although no HONO formation was found without light exposure, the light threshold for HONO formation on the asphalt surface was very low, with a total UV (TUV) of 0.7 W m⁻². HONO formation on the asphalt surface was linearly dependent on NO₂ up to 300 ppb in the presence of VOCs, but no HONO formation was observed with humified air and NO₂. HONO production was saturated at high hydrocarbon concentrations and light intensities. The calculated first-order NO₂ conversion rate to HONO on the asphalt surface was 1.2 × 10⁻⁴ s ⁻¹. The observed mean HONO emission flux was 1.3 × 10⁹ molecules cm⁻² s ⁻¹ with a similar range of those on other urban covered surfaces. The calculated vertical HONO profile using the measured HONO emission flux and 1-D steady state model revealed that the asphalt surface may account for 13% of daytime HONO in the elevated on-road pollutant concentrations in Seoul. However, we show that its HONO contribution could be much higher on real-life road surfaces directly exposed to much higher NO₂ emissions from vehicle exhaust. Full article

This study aims to analyze the seasonal number concentrations corresponding to each particle size derived from the measurements of exhausts from approximately seven million vehicles on real-world using a pair of the scanning mobility particle sizer to determine the vehicle emission rate. The actual tunnel flow coefficient was investigated for car emission rate based on the measurements of individual physical parameters (i.e., cross section area and length of the tunnel, tunnel wind speed and traffic volume). The mode of particle diameter according to temperatures in respective seasons exhibited a high correlation together with rapid changes at temperature above the breakthrough point. The temperature acted as major cause of determination of final condensation diameter, which is also dependent on diverse environmental effects comprising particle number concentration. The traffic volume of ordinary cars increased by more than twice as much in the period of Asian New Year, the traffic volume of buses/RVs/trucks decreased by more than 25% during weekdays. As a result, the particle number concentration discharged from a unit vehicle was 6.96 × 10¹² N/veh·km during weekdays, and the values of weekends appeared as 6.08 × 10¹² N/veh·km. The overall averaged particle number concentration based on the actual seasonal road measurements shows 5.82 × 10¹² N/veh·km. Full article

Among many parameters characterizing atmospheric aerosols, aerosol mass extinction efficiency (MEE) is important for understanding the optical properties of aerosols. MEE is expressed as a function of the refractive indices (i.e., composition) and size distributions of aerosol particles. Aerosol MEE is often considered as a size-independent constant that depends only on the chemical composition of aerosol particles. The famous Malm’s reconstruction equation and subsequent revised methods express the extinction coefficient as a function of aerosol mass concentration and MEE. However, the used constant MEE does not take into account the effect of the size distribution of polydispersed chemical composition. Thus, a simplified expression of size-dependent MEE is required for accurate and conventional calculations of the aerosol extinction coefficient and also other optical properties. In this study, a simple parameterization of MEE of polydispersed aerosol particles was developed. The geometric volume–mean diameters of up to 10 µm with lognormal size distributions and varying geometric standard deviations were used to represent the sizes of various aerosol particles (i.e., ammonium sulfate and nitrate, elemental carbon, and sea salt). Integrating representations of separate small mode and large mode particles using a harmonic mean-type approximation generated the flexible and convenient parameterizations of MEE that can be readily used to process in situ observations and adopted in large-scale numerical models. The calculated MEE and the simple forcing efficiency using the method developed in this study showed high correlations with those calculated using the Mie theory without losing accuracy. Full article

With global anthropogenic black carbon (BC) emissions increasing, automobiles are significantly contributing as the major source of emissions. However, the appropriate regulations of BC emissions from vehicles are not in place. This study examined BC emissions following fuel types (gasoline, liquefied petroleum gas (LPG), and diesel) and engine combustion (gasoline direct injection (GDI) and multi-port injection (MPI) for gasoline vehicles) with emission regulations. To this end, chassis dynamometer and aethalometer (AE33) were used. Driving modes created by the National Institute of Environmental Research (NIER) and emission certification modes (CVS-75 and NEDC) for vehicles in Korea were used to determine BC emissions for various vehicle speeds. In addition, the contributions of biomass and coal combustion to the data of AE33 were analyzed to determine the possibility of tracking the BC sources. MPI, LPG, and EURO 6 with diesel particulate filter (DPF) vehicles emitted the lowest BC emissions in NIER modes. Among gasoline vehicles, MPI vehicles showed the lower BC content in PM emissions. Also, older vehicles in MPI vehicles emitted the high PM and BC emissions. The BC emissions of EURO 3 vehicles without DPF were the highest as the results of previous studies, and it was found that as emissions regulations were tightened, the level of BC results of diesel vehicles became similar with MPI vehicles. The average absorption Ångström exponent (AAE) from difference emissions sources were biomass combustion (oak wood) > coal combustion (the power plant stack) > automobile emissions (gasoline, LPG, diesel). Full article

To examine the difference in the major chemical composition of fine particulate matter (PM_2.5) between two roadway sites, 24 h integrated PM_2.5 samples were simultaneously collected both 15 m (Buk-Ku District Office (BKO) site) and 150 m (Chonnam National University campus (CNU) site) away from busy roads during the summer and winter periods; these samples were taken to determine the concentrations of organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), and water-soluble inorganic species. In addition, the real-time aerosol light absorption coefficients (Abs) were measured using a dual-spot seven-wavelength aethalometer at the CNU site to evaluate the influence of traffic and biomass burning (BB) emissions on the concentrations of organic aerosol particles. The hourly NO₂ concentration was also observed at an air pollution monitoring network that is about 2 km away from the CNU site. During summer, 24 h PM_2.5 concentrations (PM_2.5 episode) which exceeded the Korean PM_2.5 standard (35 μg/m³) were linked to increases in organic matter (OM) and SO₄²⁻ concentrations that accounted for on average 35–41% and 26–30%, respectively, of the PM_2.5 at the two sites. The increased SO₄²⁻ concentration was most likely attributable to the inflow of long-range transported aerosols, rather than local production, as demonstrated by both the MODIS (Moderate Resolution Imaging Spectroradiometer) images and transport pathways of air masses reaching the sites. On the other hand, the OM, WSOC, and EC concentrations were directly attributable to traffic emissions at the sampling sites, as supported by the tight correlation between the OC and EC. A small difference between the absorption Ångström exponent (AAE) values calculated at wavelengths of 370–950 nm (AAE_370–950nm) and 370–520 nm (AAE_370–520nm), and the poor correlation of absorption coefficient by brown carbon (BrC) at 370 nm (Abs_BrC370nm) with K⁺ (R² = 0.00) also suggest a significant contribution of traffic emissions to OM. However, the wintertime PM_2.5 episode was strongly related to the enhanced OM and NO₃⁻ concentrations, which contributed 26–28% and 22–23% of the PM_2.5 concentration, respectively. It is interesting to note that there were two distinct OC/EC ratios in winter: a lower OC/EC (~3.0), which indicates a significant contribution of traffic emissions to the OC and EC, and a higher OC/EC (~6.5), which suggests an additional influence of BB emissions as well as traffic emissions at the sites. Strong correlations between the OC and EC (R² = 0.72–0.83) and the enhanced AAE_370–520nm values compared to the AAE_370–950nm support that BB emissions were also an important contributor to the wintertime OM concentrations as well as traffic emissions at the two sites. A good correlation between the gaseous NO₂ and NO₃⁻ and meteorological conditions (e.g., low wind speed and high relative humidity) suggest that the heterogeneous oxidation of NO₂ on moist particles could be an important contributor to wintertime particulate NO₃⁻ formation at the sites. The OC concentrations during summer and winter were higher at the BKO site, with a higher traffic flow and a shorter distance from the roadway than at the CNU site. However, there were slight differences in the concentrations of secondary inorganic species (NO₃⁻, SO₄²⁻, and NH₄⁺) between the sites during summer and winter. Full article

Polycyclic aromatic hydrocarbons (PAHs), an important class of hazardous airborne pollutants, are mutagenic and carcinogenic substances known to be released during the paving of asphalt. In this study, PAHs emitted from an asphalt mix plant were analyzed to investigate the effects on a suburban residential area. Black carbon, organic carbon, elemental carbon, and PAHs in fine particulate matter (PM_2.5) were analyzed in a village near the asphalt mix plant. The results of wind direction analysis revealed that the village was meteorologically affected by emissions from the asphalt mix plant. PAHs in PM_2.5 ranged from 0.51 to 60.73 ng/m³, with an average of 11.54 ng/m³. Seasonal PAHs were highest in winter, followed in order by spring, autumn, and summer. The diagnostic ratios between PAHs indicate that the source of PAHs could be incomplete combustion of petrogenic origin. The maximum black carbon concentration in the intensive periods reaches up to 14.17 μg/m³ during mix plant operation periods. Seasonal ∑BaP_TEF values based on Toxic Equivalence Factor were: winter (2.284 ng/m³), spring (0.575 ng/m³), autumn (0.550 ng/m³), and summer (0.176 ng/m³). The values are about 6.5 times higher than the concentration in another background area and more than three times higher than those in the capital city, Seoul, in the Republic of Korea. In conclusion, primary emissions from the point source can be considered the major contributor to pollution in the residential area. Full article

To reduce fine particulate matter (PM_2.5) level, the sources of PM_2.5 in terms of the composition thereof needs to be identified. In this study, the experimental burning of ten types of biomass that are typically used in Republic of Korea, collected at the regional area were to investigate the indicated organic speciation and the results obtained therefrom were applied to the chemical mass balance (CMB) model for the study area. As a result, the organic molecular markers for the biomass burning were identified as they were varying according to chemical speciation of woods and herbaceous plants and depending upon the hard- and soft characteristics of specimens. Based on the source profile from biomass burning, major sources of PM_2.5 in the study area of the present study appeared as sources of biomass burning, the secondary ions, secondary particulate matters, which is including long-distance transport, wherein the three sources occupied most over 84% of entire PM_2.5. In regard to the subject area distinguished into residential area and on roads, the portion of the biomass burning appeared higher in residential area than on roads, whereas the generation from vehicles of gasoline engine and burning of meats in restaurants, etc. appeared higher on roads comparing to the residential area. Full article

Airborne molecular contamination (AMC) represents a wide range of gaseous contaminants in the cleanroom air environment. It is difficult to monitor AMC in the cleanroom air using conventional methods in real-time due to its ultra-low concentrations, such as part-per-billion or -trillion (ppb or ppt). In this study, AMC in the real university cleanroom air environment was investigated to figure out hot spots through portable soft X-ray radiolysis detector, which converts gaseous AMC into nanoparticles (gas-to-particle conversion) under the soft X-ray irradiation. A soft X-ray was connected to a clean stainless steel chamber to convert the introduced AMC into nanoparticles, and the size distributions of nanoparticles were measured through a scanning mobility particle sizer, which consists of a differential mobility analyzer and a condensation particle counter. By converting the size distribution information into total particle volume concentrations, equivalent AMC concentrations can be calculated using an appropriate calibration curve between AMC and the total particle volume concentration. The volume concentration of nanoparticles were converted into an equivalent sulfur dioxide (SO₂, a major acidic AMC in the cleanroom air) concentration by a calibration curve between SO₂ and the particle volume concentrations. AMC levels at different locations in the cleanroom at the University of Minnesota were measured by the soft X-ray-assisted AMC detector, and revealed that several tenth-order of pptV (lower than 15 pptV) in terms of the equivalent SO₂ concentration existed in the cleanroom air environment. Full article

In this study, the source-based optical properties of polydisperse carbonaceous aerosols were determined from PM_2.5 concentrations measured at a Global Atmospheric Watch station in South Korea. The extinction and absorption coefficients of carbonaceous aerosols were calculated using the Mie theory and assuming a lognormal size distribution. Based on the mass concentration from the EPA’s Positive Matrix Factorization (PMF) receptor model, which considers five source identification and apportionment factors (biogenic source, local biomass burning, secondary organic aerosol, transported biomass burning, and mixed sources), the source-based size-resolved mass extinction and absorption efficiencies were estimated for each source using a multilinear regression model. The results show that the source-based optical properties depend on the aerosol size and physicochemical characteristics of the chemical compounds. The long-range transport of biomass burning (LBB) aerosol, which has a mass concentration of 20%, holds a 12.1–23.1% total extinction efficiency—depending on the size and refractive index—in the range of 0.1–0.5 μm in geometric mean diameter and humic-like substances (HULIS) imaginary refractive index of 0.006–0.3. Biogenic sources of aerosols with small diameters have higher mass absorption efficiencies (MAE) than other sources, depending on the size and refractive index. Full article

The vertical profile of equivalent black carbon (eBC) concentrations has been measured together with the temperature up to 130 m above ground level at several locations. A hexacopter was deployed for the measurement of eBC, and the temperature on typical days in winter, spring, summer and early autumn. We observed high eBC concentrations between 10 m and 90 m above ground level, which was related to the vertical distribution of temperature. We examined that the measurement noise could be reduced by using a box-average scheme. Furthermore, the negative values at low eBC concentration could be removed for an averaging time of 30 min or longer. Full article