On the use of an explicit chemical mechanism to dissect peroxy acetyl nitrate formation.

Peroxy acetyl nitrate (PAN) is a key component of photochemical smog and plays an important role in atmospheric chemistry. Though it has been known that PAN is produced via reactions of nitrogen oxides (NOx) with some volatile organic compounds (VOCs), it is difficult to quantify the contributions of individual precursor species. Here we use an explicit photochemical model--Master Chemical Mechanism (MCM) model--to dissect PAN formation and identify principal precursors, by analyzing measurements made in Beijing in summer 2008. PAN production was sensitive to both NOx and VOCs. Isoprene was the predominant VOC precursor at suburb with biogenic impact, whilst anthropogenic hydrocarbons dominated at downtown. PAN production was attributable to a relatively small class of compounds including NOx, xylenes, trimethylbenzenes, trans/cis-2-butenes, toluene, and propene. MCM can advance understanding of PAN photochemistry to a species level, and provide more relevant recommendations for mitigating photochemical pollution in large cities

Observations of aerosol optical properties at a coastal site in Hong Kong, South China

Temporal variations in aerosol optical properties were investigated at a coastal station in Hong Kong based on the field observation from February 2012 to February 2015. At 550 nm, the average light-scattering (151 +/- 100Mm(-1) / and absorption coefficients (8.3 +/- 6.1Mm(-1) / were lower than most of other rural sites in eastern China, while the single-scattering albedo (SSA = 0.93 +/- 0.05) was relatively higher compared with other rural sites in the Pearl River Delta (PRD) region. Correlation analysis confirmed that the darkest aerosols were smaller in particle size and showed strong scattering wavelength dependencies, indicating possible sources from fresh emissions close to the measurement site. Particles with D-p of 200-800 nm were less in number, yet contributed the most to the light-scattering coefficients among submicron particles. In summer, both Delta BC / Delta CO and SO2 / BC peaked, indicating the impact of nearby combustion sources on this site. Multi-year backward Lagrangian particle dispersion modeling (LPDM) and potential source contribution (PSC) analysis revealed that these particles were mainly from the air masses that moved southward over Shenzhen and urban Hong Kong and the polluted marine air containing ship exhausts. These fresh emission sources led to low SSA during summer months. For winter and autumn months, contrarily, Delta BC / Delta CO and SO2 / BC were relatively low, showing that the site was more under influence of well-mixed air masses from long-range transport including from South China, East China coastal regions, and aged aerosol transported over the Pacific Ocean and Taiwan, causing stronger abilities of light extinction and larger variability of aerosol optical properties. Our results showed that ship emissions in the vicinity of Hong Kong could have visible impact on the light-scattering and absorption abilities as well as SSA at Hok Tsui.Peer reviewe

Development and Application of Nanomaterials-based Photocatalytic Technology for Improvement of Urban Air Quality

&amp;lt;p&amp;gt;Air pollution is recognized as the biggest environmental health risk in urban cities, as air pollution is pervasive and hard to escape. As one of the notorious atmospheric pollutants, nitrogen oxides (NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt;, NO + NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) not only promotes the formation of ozone and secondary aerosols but also have direct adverse health effects on human beings. As a typical densely populated modern metropolis, Hong Kong can serve as a reference for world cities in terms of air pollution control. Even though air quality in Hong Kong Environment Protection Department (HKEPD) has improved over recent decades, the roadside NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; level in Hong Kong still exceeds the Hong Kong Air Quality Objectives (HKAQO), European Union Air Quality Directives (EUEQD) and the most stringent World Health Organization Air Quality Guidelines (WHOAQG). Nanomaterial-based photocatalysis that only relies upon solar energy excitation provides a sustainable solution for air pollution redemption. Generally, photocatalysts developed in the laboratory are in powder form which is not appropriate for real-world applications. However, these limitations can be overcome by coating photocatalysts on the surfaces of various substrates to immobilize those powders as films. More importantly, photocatalytic coatings are available to be supported on different substrates without changing or affecting existing settings. In this study, enhancement of NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; photocatalytic degradation ability and solar light utilization were implemented in a reformative Titanium Dioxide (TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) film. Hydrogen peroxide solution was utilized to peptize the crystallized nanoparticles around 5-6 nm at room temperature instead of the traditional calcination process at high temperatures, which limited the commercialization due to the expensiveness of heating. Moreover, the nanosized TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; film was expected to provide more active sites for reactions, which contributes to a promising photocatalytic degradation ability. Based on ISO 22197-1 evaluation standards, the as-developed photocatalytic coating possesses a NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; degradation rate of 4.402 mg*m&amp;lt;sup&amp;gt;-2&amp;lt;/sup&amp;gt;h&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt; when applied on the concrete surface, which was higher than Degussa (Evonik) P25 and other commercial coating products at the same conditions. An artificial weather resistance test investigation implies the photocatalytic coating will provide a strong bonding interaction with substrate materials which is beneficial to the lifetime of the coating. Further investigating from a 180-day field trial in a roadside environment in Hong Kong, the as-developed coating concrete specimen presented about 5% of attenuation in the first 30 days and sustained 13.9%-18.5% photocatalytic activity after the entire 180-day outdoor exposure. The application of photocatalytic coatings is supposed to convert the roadside NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; compounds to NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;-&amp;lt;/sup&amp;gt; and NO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;-&amp;lt;/sup&amp;gt; which are harmless in small quantities and would be washed away by water droplets. In response to practical demands, functional nanomaterials-based photocatalytic technology has been gradually promoted as a green strategy for improvements in the air quality of megacities all over the world.&amp;lt;/p&amp;gt;</jats:p

High loadings and source strengths of organic aerosols in China

Nation-wide studies of organic aerosols were conducted on a molecular level in 15 Chinese cities. The results showed strikingly high levels of organic compounds (e.g., annual concentrations of polycyclic aromatic hydrocarbons, phthalates, sugars and diacids are 110, 370, 400 and 830 ng m−3, respectively), especially in the mid-west region during winter (up to 125 μg m−3 organic carbon). Fossil fuel combustion and/or biomass burning products are 3−30 times more abundant in winter than in summer. In contrast, significant quantity of phthalates (168−2200 ng m−3) was detected in summer. Concentrations of the pollutants are generally 1−3 orders of magnitude higher than those in developed countries. Their source strengths are characterized in winter by fossil fuel combustion, followed by secondary oxidation, plant wax emissions and biomass burning, whereas in summer by secondary oxidation, followed by fossil fuel combustion and plastic emissions

Characteristics of Fine Particulate Matter (PM2.5)-Bound n-Alkanes and Polycyclic Aromatic Hydrocarbons (PAHs) in a Hong Kong Suburban Area

PM2.5 samples were collected at Tung Chung (TC), Hong Kong, during four nonconsecutive months in 2011/2012 to determine the concentrations, seasonal variations, and potential sources of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes (n-C15-n-C35). Samples were analyzed using the thermal desorption gas chromatography/mass spectrometry (TD-GC/MS) method. The concentrations of particulate PAHs ranged from 1.26&ndash;13.93 ng/m3 with a mean value of 2.57 ng/m3, dominated by 4-ring species. Phenanthrene (Phe) and fluoranthene (Flu) were the two most abundant species, accounting for 13% and 18%, respectively. The dominant sources of PAHs were coal and biomass burning. The inhalation cancer risk value in our study exceeded 1 &times; 10&minus;6 but was below 1 &times; 10&minus;4, implying that the inhalation cancer risk of PAHs at the TC site is acceptable. The average concertation of n-alkanes was 103.21 ng/m3 (ranging from 38.58 to 191.44 ng/m3), and C25 was the most abundant species. Both PAHs and n-alkanes showed higher concentrations in autumn and winter whilst these values were lowest in summer. The carbon preference index (CPI) and percent contribution of wax n-alkanes showed that biogenic sources were the major sources. The annual average contributions of higher plant wax to n-alkanes at TC were over 40%