Aerosol and Air Quality Research
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社團法人台灣氣膠研究學會,正常發行
選擇卷期
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Natural ventilation can be categorized into single-sided ventilation and cross-ventilation. Based on the air flow mechanism of a single-sided wind-driven natural ventilation, the effective ventilation flow rates in buildings are different from the air flow rates through openings. The mixing coefficient or ventilation efficiency is defined by the ratio of these flow rates, indicating the effective ventilating ability of a single-sided ventilation, similar to the effect of penetration depth of fresh air. This paper provides a detailed analysis of ventilation effectiveness in a building with a single opening based on numerical simulations. The simulation was validated by a study of an existing case. By numerical calculation, the air flow rates through openings and the effective ventilation flow rates in buildings were compared. Effects of various influencing parameters, such as wind speed, opening location, opening area and aspect ratio of windward wall on ventilation efficiency were evaluated. An estimated mixing coefficient has been established by the modelling, which would be beneficial for the predication of the short-circuit ratio of ventilation rate through openings.
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Particulate sulphate (pSO_4^(2-)) is an atmospheric pollutant known to affect human/environmental health and global radiative-forcing. The Rio Tinto (RT) aluminium smelting facility in Kitimat, British Columbia, is the primary source of sulphur dioxide (SO_2) emissions to the surrounding Kitimat Valley, a relatively isolated and unpolluted region. A network of active two-stage filter-packs and passive-diffusive samplers was established between June 2017 to October 2018 with the objective to evaluate the spatiotemporal variation and relative contribution of pSO_4^(2-) to total anthropogenic atmospheric oxidized sulphur (SO_x = SO_2 + pSO_4^(2-)). Average pSO_4^(2-) across all sites (n = 9) was 0.41 μg m^(-3) (24-48 hour exposures) and ranged from 0.03 to 2.03 μg m^(-3). In contrast, average filter-pack SO_2 ranged from 0.11 to 8.9 μg m^(-3) (during the same exposure periods). The filter-pack pSO_4^(2-)/SO_x concentration ratio (F_s) increased downwind of the smelter, indicating that the relative concentration of pSO_4^(2-) increased with distance from the smelter. Furthermore, the increasing pSO_4^(2-)/vanadium (V) ratio (used as a tracer of smelter emissions) relative to distance confirmed particulate formation was occurring within the emission plume during the sampling period. Irrespective of in-plume aerosol formation, pSO_4^(2-) contributed a relatively minor fraction of total atmospheric SO_x within the emission plume (field campaign averages F_s ＜ 20%; pSO_4^(2-) ＜ 0.1 μg S m^(-3); SO_2 ＞ 1.0 μg S m^(-3)).
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Levels, compositions, sources and health risk of PM_(2.5)-bound PAHs were measured at a regional monitoring site of Huang-gang in the winter of 2018. Samples were collected every morning, afternoon, evening and late night (LN). The average concentrations of PM_(2.5) and PAHs were 110.4 ± 48.3 μg m^(-3) and 25.6 ± 12.0 ng m^(-3), respectively. The concentration of PM_(2.5) was in the order of evening ＞ morning ＞ afternoon ＞ LN, while PAHs concentration was in the order of evening ＞ LN ＞ morning ＞ afternoon. According to PM_(2.5) concentration and its changing trend, the haze can be divided into three stages: early (low concentration, January 13-15, EHZ), medium (high concentration, January 16-22, MHZ) and late (concentration decreased rapidly, January 23-24, LHZ). A positive correlation (P ＜ 0.01) was observed between PM_(2.5) and Σ_(16)PAHs concentration only in MHZ. Besides, PAHs concentration was positively related to NO_x concentration, CO concentration and temperature but negatively correlated with RH, independent of O_3 concentration. The ratios of OC/EC indicated that the secondary aerosol had a great influence on the formation of haze. Three sources of PAHs including traffic emission, coal combustion and biomass combustion were extracted and quantified, accounting for 54.4%, 13.3% and 32.3% of PAHs, respectively. Potential source contribution function (PSCF) and concentration weighted trajectory (CWT) indicated the transmission of PM_(2.5) from Wuhan and local pollutant emission were crucial to the formation of haze. BaP_(eq) concentration combined with ILCR values was used to evaluate health risk and the results showed this haze had potential health risk to both adults and children.
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Seasonal variation and sources of elements bound to urban aerosol were studied. Fine (PM_(2.5)) and submicron (PM_1) aerosol was collected at 2-week campaigns during four seasons in 2018. The total concentration of 21 elements accounted on average for 3.5% of the total PM_(2.5) mass concentration and 2.0% of the total PM_1 mass concentration. Seasonal differences in the element concentrations in PM_1 and PM_(2.5) were found. Most elements in both aerosol size fractions had a higher concentration in winter or autumn than in summer or spring. Enrichment factor analysis showed extremely highly enriched Cd, Sb and Se in both fractions. Positive matrix factorization (PMF) analysis revealed 3 sources (residential heating, resuspension and anthropogenic background) for PM_1 and 3 sources (residential heating, resuspension and brake abrasion) for PM_(2.5) aerosol in Brno. In addition, health risk assessment of possibly toxic elements was calculated.
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In this study, the atmospheric total-PCDD/Fs-WHO_(2005)-TEQ concentrations, gas-particle partitioning, PM_(2.5) concentration, PM_(2.5)-bound total PCDD/Fs-WHO_(2005)-TEQ content and dry deposition flux in Shanghai and Nanjing were investigated from 2018-2020. In Shanghai, the total PCDD/Fs-WHO_(2005)-TEQ concentration dropped from 0.0291 pg-WHO_(2005)-TEQ m^(-3) from 2018-2019 to 0.0250 pg-WHO_(2005)-TEQ m^(-3) in 2020, while in Nanjing, it dropped from 0.0423 pg-WHO_(2005)-TEQ m^(-3) to 0.0338 pg-WHO_(2005)-TEQ m^(-3). The average concentrations of PCDD/Fs-WHO_(2005)-TEQ in spring and winter in Shanghai and Nanjing were 47.6% and 53.8% higher than those in summer, respectively. From 2018-2019, the average particle phase fractions of total-PCDD/Fs-WHO_(2005)-TEQ in Shanghai and Nanjing were 50.3% and 57.5%, respectively, while in 2020, they were 47.8% and 55.1%, respectively. From 2018-2019, the average PM_(2.5)-bound total PCDD/Fs-WHO_(2005)-TEQ content was 0.342 and 0.493 ng-WHO_(2005)-TEQ g^(-1) in Shanghai and Nanjing, respectively, while in 2020, it was 0.312 and 0.489 ng-WHO_(2005)-TEQ g^(-1), respectively. In Shanghai and Nanjing, the average PM_(2.5)- bound total PCDD/Fs-WHO_(2005)-TEQ content in spring and winter was 77.5% and 73.2% higher than that in summer, respectively. From 2018-2019, the dry deposition flux of total-PCDD/Fs-WHO_(2005)-TEQ was 316.3 and 460.5 pg WHO_(2005)-TEQ m^(-2) month^(-1) in Shanghai and Nanjing, respectively, while in 2020, it was 272.5 and 368.4 pg WHO_(2005)-TEQ m^(-2) month^(-1), respectively. The average dry deposition flux of total-PCDD/Fs-WHO_(2005)-TEQ in spring and winter was 47.6% and 53.8% higher than that summer in Shanghai and Nanjing, respectively. The above results indicate that COVID-19 in 2020 had a positive effect on air quality improvement in PCDD/Fs. On average, more than 98.88% of the total PCDD/Fs-WHO_(2005)-TEQ dry deposition flux was primarily contributed by the particle phase. This was attributed to the fact that dry deposition of particle phase PCDD/Fs was mainly due to gravitational settling accompanied by higher dry deposition velocities, while the gas phase PCDD/Fs were deposited mostly by diffusion at a lower dry deposition velocity.
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Ambient air pollution caused by fine particulate matter (PM) and trace gases is a pressing topic as it affects the vast majority of the world's population, with a particularly heavy influence in densely populated urban environments. Alongside nitrogen oxides (NO_x) and PM, ammonia (NH_3) is also a relevant air pollutant due to its role as a precursor of particulate ammonium. This is a study about the short-term temporal dynamics of urban NH_3 concentrations in Münster, northwest Germany, the role of road traffic and agriculture as NH_3 sources and about the importance of ammonia for secondary particle formation (SPF). The NH_3 mixing ratio was rather high (mean: 17 ppb) compared to other urban areas and showed distinct diurnal maxima around 10 a.m. and during the night at 9 p.m. The main source for ammonia in Münster was agriculture, but road traffic also contributed through local emissions from vehicle catalysts. NH_3 from surrounding agricultural areas accumulated in the nocturnal boundary layer and contributed to SPF in the city center. Modeled emissions of NH_3 as estimated by the Handbook for Emission Factors in combination with traffic counts were in the same magnitude for NH_3. The size-resolved chemical composition of inorganic ions in PM_(10) was dominated by NH_4^+ (8.66 μg m^(-3)), followed by NO_3^- (3.89 μg m^(-3)), SO_4^(2-) (1.58 μg m^(-3)) and Cl^- (1.33 μg m^(-3)). Particles in the accumulation range (diameter: 0.1- 1 μm) showed the highest inorganic ion concentrations. The ammonium neutralization index J (111%) indicated an excess of NH_4^+ leading to mostly alkaline PM. High ammonia emissions from surrounding agricultural areas combined with large amounts of NO_x from road traffic play a crucial role for SPF in Münster.
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The hygroscopicity and oxidation level of secondary organic aerosol (SOA) produced in an atmospheric simulation chamber were measured as a function of volatility. The experimental setup combines thermodenuding, isothermal dilution, aerosol mass spectroscopy, and size-resolved cloud condensation nuclei measurements to separate the SOA by volatility and then measure its physical (hygroscopicity via the hygroscopicity parameter, κ) and chemical (oxidation level via the oxygen-to-carbon ratio, O:C) properties. The technique was applied to SOA from the ozonolysis of α-pinene, limonene, and cyclohexene. The O:C and κ of the α-pinene ozonolysis SOA decreased as volatility decreased. The semi-volatile and the low volatility organic compounds produced during limonene ozonolysis have similar O:C and κ values, but the corresponding extremely low volatility organic compounds have significantly lower oxygen content and hygroscopicity. The average O:C of the cyclohexene ozonolysis SOA increased, but the average κ decreased as volatility decreased. These results suggest that some organic aerosol (OA) systems have a more complex relationship between hygroscopicity, oxidation level, and volatility than originally thought. The two-dimensional volatility basis set framework can help in integrating these results and providing explanations of the measured hygroscopicity. Use of this technique with different OA systems, both laboratory and ambient, can supply parameters that can be incorporated in atmospheric chemical transport models.
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Atmospheric dust aerosols are known to affect the air quality and public health as well as climate and weather systems. An increasing number of modeling studies have related ice nucleation with the number concentrations of dust particles with a diameter larger than 500 nm (N_(D,d＞500nm)). In this paper, the seasonal variation, vertical properties, and long-term trend of N_(D,d＞500nm) over the Taiwan region are analyzed, using simulations from a global chemical transport model with size-resolved particle microphysics. Over Taiwan, N_(D,d＞500nm) shows a bimodal seasonal variation distribution with two peaks in spring (March-May) and fall-early winter (October-December). In the different seasons, N_(D,d＞500nm) varies by about one order of magnitude from summer to spring (0.06-1.23 cm^(-3) in the boundary layer, 0.03-0.55 cm^(-3) in the middle and lower troposphere, and 0.006-0.03 cm^(-3) in the upper level). Vertically, N_(D,d＞500nm) profiles show the unimodal distribution, with the highest N_(D,d＞500nm) appears at ~1 km and decreasing with altitude. From surface to high levels, the frequencies of intense dust events decrease in fall (September-November) and increase in summer months (June-August). The long-term model results suggest a decreasing trend of the strong dust event frequencies and annual mean N_(D,d＞500nm) over Taiwan in the last two decades. From 1999 to 2018, the number of strong dust event days and N_(D,d＞500nm) decreased by 40-43% and 37-54%, respectively, under 4 km, and the decline is weaker at higher altitudes. The analysis suggests that these decrease trends are caused by the declining Asian dust emissions.
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To control the spread of the coronavirus (COVID-19) pandemic, the Government of India imposed various phases of lockdown starting from the third week of March 2020. Improvement in city air quality has emerged as a benefit of this lockdown in India. The objective of this paper is to quantify the health benefits due to this lockdown. PM_(2.5) concentrations in nonattainment cities (NACs) in Uttar Pradesh and the Delhi-National Capital Region (NCR) in North India were studied. Data from prelockdown and the various lockdown phases were compared, with 2019 as a benchmark. Compared with those in 2019, the PM_(2.5) concentrations during lockdown Phase 1 were approximately 44.6% lower for cities in Uttar Pradesh and approximately 58.5% lower for the Delhi-NCR. The health impacts of particle inhalation were quantified using the multiple-path particle dosimetry and AirQ+ models, which revealed that the most considerable improvement was during lockdown Phase 1. Among the prelockdown and lockdown phases, Phase 1 exhibited the minimum PM_(2.5) concentration and thus the greatest health benefits. For the selected cities, the concentration of particle deposition in the tracheobronchial region of human lungs showed its maximum reduction during lockdown Phase 1(30.14%). Furthermore, the results highlighted a decrease of 29.85 deaths per 100,000 persons during lockdown Phase 1, primarily due to the reduction in PM_(2.5) concentrations. This quantification of the health benefits due to a decrease in PM_(2.5) may help policymakers implement suitable control measures, especially for NACs, where the respirable particulate matter concentrations remain very high.
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Size-segregated ultrafine particles (UFPs) in diesel exhaust were investigated to characterize carbonaceous substances, metals, and organic compounds originating from a medium-duty diesel engine dynamometer using the 13 driving mode. Organic carbon (OC) and elemental carbon (EC) peaked at 330-550 nm, but the OC/EC ratio showed two peaks in the ultrafine and accumulation modes. The distribution trend of metal elements was opposite to that of the size-segregated OC/EC ratio. The amounts of toxic Pb, As, and Cd were less than 0.03-2.5% in diesel exhaust particles (DEPs), but their cumulative fractions in the ultrafine mode exceeded 50%. Most organic compounds (76.6%) and alkanes (67.0%) were emitted in the accumulation mode (170-1000 nm). More than 70% of the identified polycyclic aromatic hydrocarbons (PAHs) were emitted in the accumulation mode (94-1000 nm), with phenanthrene being the most abundant. Two significant size ranges of toxicity equivalent quantity peaks in the ultrafine (34-66 nm) and accumulation (170-330 nm) modes were observed for the size-segregated DEPs. Contrary to the trends for PAHs and organic compounds, the identifiable nitrogen-containing polycyclic aromatic compounds were more abundant in the ultrafine mode. Overall toxicity was high as UFPs can be deposited with high efficiency throughout the human respiratory tract.