Arthur P.S. Lau

Growth and Shrinkage of New Particles in the Atmosphere in Hong Kong

Grown nucleated particles > 50 nm in diameter are an important source of cloud condensation nuclei (CCN) and when the size is > 100 nm, they can also have direct influence on the climate. In this study, the nucleation and growth of new particles in the atmosphere in Hong Kong were investigated during dry season (monthly averaged RH < 75%). The maximum size of grown nucleated particles was generally less than 40 nm during new particle burst and growth events. The exception, accounting for ∼ 20% of all burst and growth events, was those induced by strong photochemical reactions, in which subsequent particle shrinkage occurred. Temporal particle and gas concentration variability and meteorological conditions support the occurrence of particle shrinkage. The shrinkage rate calculated (∼ 8 nm h–1) was close to the growth rate. The observation of particle shrinkage sheds new light on particle transformation dynamics and it would add to the understanding of particle behavior in the atmosphere.

Characterization of Organic Particles from Incense Burning Using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer

Incense burning is a common ritual in Asian communities both indoors in residential homes and outdoors in temple premises. Organic particles from burning of incense sticks, incense coils, and mosquito coils after extensive dilution (>1000×) were characterized by the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The obtained mass spectra in general resemble those reported for biomass burning aerosols. Ion peaks with m/z values higher than 100 accounted for 15%–25% of the organic signals in the unit-mass-resolution (UMR) mass spectra. In the high-resolution (HR) mass spectra, the ion peaks at m/z 60 and 73 are found to be related to the sugar anhydrides as in particles from other biomass burning processes. In addition, the ion peaks at m/z 107, 121, 137, 151, 167, and 181, some of which (e.g., m/z 137 and 167) have been observed in particles from biomass burning but not yet assigned, were assigned to lignin-related components. Elemental analysis from the HR data reveals that a large portion of particulate organics from incense burning are oxygenated (O/C between 0.3 and 0.5) and unsaturated (and/or cyclic) in nature. Results from this study also highlight that mass spectra from HR-ToF-AMS measurements concerning primary emissions such as incense burning contain very useful information in the high m/z (>100) region about the chemical characteristics of those primary organic particles. Copyright 2012 American Association for Aerosol Research

Surface Chemical Composition of Size-Fractionated Urban Walkway Aerosols Determined by X-Ray Photoelectron Spectroscopy

Most aerosol chemical characterization studies to date involve bulk particle analysis. The surface chemical and physical properties of aerosol particles have rarely been analyzed, despite the particles’ potential health impacts and interactions with gas in the atmosphere. Aerosol particles ranging from 0.056 to 10 μm in size collected using a 10-stage impactor sampler from a busy walkway in a downtown area of Hong Kong were analyzed using X-ray photoelectron spectroscopy (XPS), a technique providing both elemental and chemical state information about the particle surfaces. Six key elements were detected: nitrogen (N), sulfur (S), calcium (Ca), silicon (Si), oxygen (O), and carbon (C). Carbon was the dominant species on the surfaces of all particles regardless of their sizes. A higher carbon concentration was found on the surfaces of the 0.056–0.32 μm particles. The N, Si, Ca, and O concentrations were higher on the surface of the 3.2–10 μm particles than in the smaller size fractions. Sulfur was mainly found on the surface of the 0.32–1.8 μm particles. High-resolution scans of C, N, and S were obtained to provide chemical state information about these elements. Aromatic C-H and aliphatic C-H were found to be the major carbon chemical states. Fullerenic carbon was detected on the surfaces of the finest (0.056–0.32 μm) particles. Oxygen- and nitrogen-containing organics were found on the surfaces of the 0.32–1.8 μm particles. Sulfur was present in the form of sulfates as expected. Ammonium salts, amide, and nitrate were found to form especially on the surfaces of aerosol particles in the nucleation, accumulation, and coarse modes, respectively. Silicates and carbonates were only discovered on the surfaces of coarse-mode particles (3.2–10 μm). The results suggest that both the chemical elements and their chemical states were significantly dependent on the size of the aerosol particles. Copyright 2013 American Association for Aerosol Research

Acid-catalyzed condensed-phase reactions of limonene and terpineol and their impacts on gas-to-particle partitioning in the formation of organic aerosols.

We investigated the condensed-phase reactions of biogenic VOCs with C double bond C bonds (limonene, C(10)H(16), and terpineol, C(10)H(18)O) catalyzed by sulfuric acid by both bulk solution (BS) experiments and gas-particle (GP) experiments using a flow cell reactor. Product analysis by gas chromatography-mass spectrometry (GC-MS) showed that cationic polymerization led to dimeric and trimeric product formation under conditions of relative humidity (RH) <20% (in the GP experiments) and a sulfuric acid concentration of 57.8 wt % (in the BS experiments), while hydration occurred under conditions of RH > 20% (in the GP experiments) and sulfuric acid concentrations of 46.3 wt % or lower (in the BS experiments). Apparent partitioning coefficients (K(p,rxn)) were estimated from the GP experiments by including the reaction products. Only under extremely low RH conditions (RH < 5%) did the values of K(p,rxn) ( approximately 5 x 10(-6) m(3)/microg for limonene and approximately 2 x 10(-5) m(3)/microg for terpineol) substantially exceed the physical partitioning coefficients (K(p) = 6.5 x 10(-8) m(3)/microg for limonene and =2.3 x 10(-6) m(3)/microg for terpineol) derived from the absorptive partitioning theory. At RH higher than 5%, the apparent partitioning coefficients (K(p,rxn)) of both limonene and terpineol were in the same order of magnitude as the K(p) values derived from the absorptive partitioning theory. Compared with other conditions including VOC concentration and degree of neutralization (by ammonium) of acidic particles, RH is a critical parameter that influences both the reaction mechanisms and the uptake ability (K(p,rxn) values) of these processes. The finding suggests that RH needs to be considered when taking the effects of acid-catalyzed reactions into account in estimating organic aerosol formation from C double bond C containing VOCs.

A Re-Evaluation on the Atmospheric Significance of Octanal Vapor Uptake by Acidic Particles: Roles of Particle Acidity and Gas-Phase Octanal Concentration

An electrodynamic balance was used to investigate the uptake of octanal vapor by single sulfuric acid droplets levitated under various relative humidity (RH) conditions and gas-phase octanal concentrations. In the high octanal concentration experiments (200–300 ppm), we observed that the organic mass yield depended on the acidity of the sulfuric acid droplets and significant uptake of octanal only occurred when the RH was about 10% (H 2 SO 4 wt% ∼ 64%). Furthermore, repartitioning of only a portion of condensed organic compounds was observed after active dilution with octanal-free compressed air, indicating that low-volatility products had formed and that repartitioning is important in affecting the organic mass fraction and chemical composition of atmospheric organic aerosols. When a relatively lower octanal concentration (700–900 ppb) was used, no significant uptake of octanal vapor by the sulfuric acid droplets was observed even at 10% RH with long exposure time (>25 h). Our findings suggest that both particle acidity and gas-phase octanal concentration are the critical factors that influence the organic mass yield of levitated acidic droplets. Because of the severe conditions of low RH and high octanal conditions required to effect the reactions, the reactive uptake of aldehydes, especially those that have chemical structures and properties very similar to octanal, into acidic particles may not be an important pathway in secondary organic aerosol formation under actual atmospheric conditions.

Frequent use of household cleaning products is associated with rhinitis in Chinese children

BACKGROUND Despite the popular use of household cleaning products worldwide, there is no published study investigating the health effects of these products on rhinitis in children. OBJECTIVE We sought to investigate the household use of cleaning products and rhinitis patterns in Chinese children. METHODS A total of 2299 children were recruited from 21 primary schools with wide geographic coverage in Hong Kong. Self-administered questionnaires were completed by parents/guardians to collect detailed information on respiratory symptoms and household use of 14 types of chemical cleaning products, as well as clean water. Students were categorized into 4 mutually exclusive rhinitis patterns (never, occasional, frequent, and persistent). The total chemical burden (TCB) score was used as the exposure indicator by calculating the total time of exposure to the 14 cleaning products. Multinomial logistic regression was used to assess the relationship between rhinitis patterns and the use of household cleaning products. RESULTS Every 10-unit increment of TCB score was associated with an increase in the odds of occasional (odds ratio [OR], 1.21; 95% CI, 1.05-1.41), frequent (OR, 1.36; 95% CI, 1.13-1.60), and persistent (OR, 1.21; 95% CI, 1.01-1.56) rhinitis after adjustment for a wide range of potential confounders. Compared with the children within the lowest tertile of TCB scores, the adjusted ORs of occasional, frequent, and persistent rhinitis in children within the highest tertile were 1.29 (95% CI, 1.01-1.65), 1.97 (95% CI, 1.40-2.76), and 1.67 (95% CI, 1.10-2.54), respectively. CONCLUSION Frequent use of chemical cleaning products at home is associated with an increase in the odds of rhinitis in Chinese primary school children.

Quantification of Airborne Elemental Carbon by Digital Imaging

Black carbon emitted from vehicles or industrial plants is a very common phenomenon observed by high school students. A cost effective and user friendly measurement protocol will greatly enhance school students’ capability to investigate the black carbon pollutant in their ambient environments, and hence their awareness to environmental protection. This study shows the potential of applying digital imaging as an alternative method to measure airborne elemental carbon (EC). Aerosols were collected on filters and the blackness of the filters was digitalized into RGB values using an office scanner. It was found that maximum value of transformed R, G and B values (255 – R, 255 – G and 255 – B, respectively), max {R’,G’,B’}, was power-law related with the EC loading of the filter (R2 = 0.85, n = 55). The power-law relationship between the max{R’,G’,B’} and EC loading could be applied as a cost effective and user friendly method to quantify EC by high school students. Using this method, the sampling flowrate and duration should be controlled so that the max{R’,G’,B’} of the filter samples lie in the optimal range between 40 and 170 to minimize the uncertainty. For samples within this range, the average percentage difference between the results of this method and the results from conventional thermal-optical method was found to be only 10.3%, which is close to common research grade instruments.

Dietary Patterns and the Risk of Rhinitis in Primary School Children: A Prospective Cohort Study

This study was to investigate the association between dietary patterns and rhinitis in primary school children. 1,599 students without rhinitis at baseline survey were selected from a primary school children cohort. Information on food consumption, respiratory symptoms, and confounders was collected using questionnaires. Dietary patterns were defined using principal component analysis. Logistic regression was performed to calculate odds ratio (OR) with 95% confidence intervals (95% CI). The incidence of rhinitis during 12 months follow-up was 21.2%. Three patterns were extracted and labeled as pattern I, II and III. Dietary pattern II which had higher factor loadings of legumes, butter, nuts and potatoes was associated with an increased risk of rhinitis (OR: 1.34, 95% CI: 1.01–1.87) when the highest tertile of pattern score was compared to the lowest tertile, after adjusted for confounders. Besides, every 1-unit increase of score of pattern II was also associated with an increased risk of rhinitis (OR: 1.19, 95% CI: 1.05–1.35). Neither pattern I nor Pattern III was observed to be associated with risk of rhinitis. A diet with higher levels of consumption of legumes, butter, nuts and potatoes may increase the risk of allergic rhinitis in primary school children.

Household cleaning products and the risk of allergic dermatitis: A prospective cohort study with primary-school children

Household cleaning products are widely used by the public, but limited data have been obtained on whether their use induces allergic dermatitis in children.