No abstract

While current research has demonstrated that the operation of some laser printers results in emission of high concentrations of ultrafine particles, fundamental gaps in knowledge in relation to the emissions still remain. In particular, there have been no answers provided to questions such as the following: (1) What is the composition of the particles? (2) What are their formation mechanisms? (3) Why are some printers high emitters, while others are low? Considering the widespread use of printers and human exposure to these particles, understanding the process of particle formation is of critical importance. This study, using state-of-the-art instrumental methods, has addressed these three points. We present experimental evidence that indicates that intense bursts of particles are associated with temperature fluctuations and suggest that the difference between high and low emitters lies in the speed and sophistication of the temperature control. We have also shown, for the first time, that the particles are volatile and are of secondary nature, being formed in the air from VOC originating from both the paper and hot toner. Some of the toner is initially deposited on the fuser roller, after which the organic compounds evaporate and then form particles, through one of two main reaction pathways: homogeneous nucleation or secondary particle formation involving ozone.

Abstract. Filter samples of fine particulate matters were collected at four sites in northern China (urban, rural, and mountain) in summer and winter, and the contents of nine nitrated phenols were quantified in the laboratory with the use of ultra-high-performance liquid chromatography coupled with mass spectrometry. During the sampling periods, the concentrations of particulate nitrated phenols exhibited distinct temporal and spatial variation. On average, the total concentration of particulate nitrated phenols in urban Jinan in the wintertime reached 48.4 ng m −3 , and those in the summertime were 9.8, 5.7, 5.9, and 2.5 ng m −3 in urban Jinan, rural Yucheng and Wangdu, and Mt. Tai, respectively. The elevated concentrations of nitrated phenols in wintertime and in urban areas demonstrate the apparent influences of anthropogenic sources. The positive matrix factorization receptor model was then applied to determine the origins of particulate nitrated phenols in northern China. The five major source factors were traffic, coal combustion, biomass burning, secondary formation, and aged coal combustion plume. Among them, coal combustion played a vital role, especially at the urban site in the wintertime, with a contribution of around 55 %. In the summertime, the observed nitrated phenols were highly influenced by aged coal combustion plumes at all of the sampling sites. Meanwhile, in remote areas, contributions from secondary formation were significant. Further correlation analysis indicates that nitrosalicylic acids were produced mostly from secondary formation that was dominated by NO 2 nitration.

Abstract. Marine atmosphere is usually considered to be a clean environment, but this study indicates that the nearcoast waters of the South China Sea (SCS) suffer from even worse air quality than coastal cities. The analyses were based on concurrent field measurements of target air pollutants and meteorological parameters conducted at a suburban site (Tung Chung, TC) and a nearby marine site (Wan Shan, WS) from August to November 2013. The observations showed that the levels of primary air pollutants were significantly lower at WS than those at TC, while the ozone (O 3 ) value was greater at WS. Higher O 3 levels at WS were attributed to the weaker NO titration and higher O 3 production rate because of stronger oxidative capacity of the atmosphere. However, O 3 episodes were concurrently observed at both sites under certain meteorological conditions, such as tropical cyclones, continental anticyclones and sea-land breezes (SLBs). Driven by these synoptic systems and mesoscale recirculations, the interaction between continental and marine air masses profoundly changed the atmospheric composition and subsequently influenced the formation and redistribution of O 3 in the coastal areas. When continental air intruded into marine atmosphere, the O 3 pollution was magnified over the SCS, and the elevated O 3 (> 100 ppbv) could overspread the sea boundary layer ∼ 8 times the area of Hong Kong. In some cases, the exaggerated O 3 pollution over the SCS was recirculated to the coastal inshore by sea breeze, leading to aggravated O 3 pollution in coastal cities. The findings are applicable to similar mesoscale environments around the world where the maritime atmosphere is potentially influenced by severe continental air pollution.

Toxic air pollutants in street canyons are important issues concerning public health especially in some large Asian cities like Guangzhou. In 1998 o18% of Guangzhou citizens used public transportation modes, with a majority commuting on foot (42%) or by bicycle (22%). Of the pedestrians, 57% were either senior citizens or students. In the present study, we measured toxic air pollutants while walking along urban streets in Guangzhou to evaluate pedestrian exposure. Volatile organic compounds (VOCs) were collected with sorbent tubes, and PM 10 and CO were measured simultaneously with portable analyzers. Our results showed that pedestrian exposure to PM 10 (with an average of 303 mg m À3 for all samples) and some toxic VOCs (for example, benzene) was relatively high. Monocyclic aromatic hydrocarbons were found to be the most abundant VOCs, and 71% of the samples had benzene levels higher than 30 mg m À3. Benzene, PM 10 and CO in walk-only streets were significantly lower (po0.05) than in traffic streets, and the differences in exposure levels between new urban streets and old urban streets were highly significant (po0.01). Pedestrian exposure to toxic VOCs and PM 10 was higher than those reported in other public transportation modes (bus and subway). The good correlations between BTEX, PM 10 and CO in the streets indicated that automotive emission might be their major source. Our study also showed that the risk to pedestrians due to air pollution was misinterpreted by the reported air quality index based on measurement of SO 2 , NO x and PM 10 in the government monitoring stations. An urban roadside monitoring station might be needed by air quality monitoring networks in large Asian cities like Guangzhou, in order to survey exposure to air toxics in urban roadside microenvironments.

An increasing number of researchers have hypothesized that ozone may be involved in the particle formation processes that occur during printing, however no studies have investigated this further. In the current study, this hypothesis was tested in a chamber study by adding supplemental ozone to the chamber after a print job without measurable ozone emissions. Subsequent particle number concentration and size distribution measurements showed that new particles were formed minutes after the addition of ozone. The results demonstrated that ozone did react with printer-generated volatile organic compounds (VOCs) to form secondary organic aerosols (SOAs). The hypothesis was further confirmed by the observation of correlations among VOCs, ozone, and particles concentrations during a print job with measurable ozone emissions. The potential particle precursors were identified by a number of furnace tests, which suggested that squalene and styrene were the most likely SOA precursors with respect to ozone. Overall, this study significantly improved scientific understanding of the formation mechanisms of printer-generated particles, and highlighted the possible SOA formation potential of unsaturated nonterpene organic compounds by ozone-initiated reactions in the indoor environment.

Abstract. Over the past 10 years (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014), ground-level O 3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NO x = NO + NO 2 ), total volatile organic compounds (TVOCs), and carbon monoxide (CO). To explain the contradictory phenomena, an observation-based box model (OBM) coupled with CB05 mechanism was applied in order to understand the influence of both locally produced O 3 and regional transport. The simulation of locally produced O 3 showed an increasing trend in spring, a decreasing trend in autumn, and no changes in summer and winter. The O 3 increase in spring was caused by the net effect of more rapid decrease in NO titration and unchanged TVOC reactivity despite decreased TVOC mixing ratios, while the decreased local O 3 formation in autumn was mainly due to the reduction of aromatic VOC mixing ratios and the TVOC reactivity and much slower decrease in NO titration. However, the decreased in situ O 3 formation in autumn was overridden by the regional contribution, resulting in elevated O 3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O 3 formation was VOClimited in all seasons, and that the long-term O 3 formation was more sensitive to VOCs and less to NO x and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O 3 formation decreased in all seasons of these years, particularly in autumn, probably due to the effective control of solvent-related sources. In contrast, the contributions of alkenes increased, suggesting a continuing need to reduce traffic emissions. The findings provide updated information on photochemical pollution and its impact in Hong Kong.

Abstract. To investigate the atmospheric oxidative capacity (AOC) in forested high mountain areas adjacent to the photochemistry-active Pearl River Delta (PRD) region in southern China, one-month online observations of isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were conducted at a national background station in Nanling Mountains in summer 2016. The results showed that the observed daytime isoprene levels (377±46 pptv) were significantly lower in comparison with other forest sites within and outside China, although the sampling site was surrounded with subtropical evergreen broad-leaved trees which are strong isoprene emitters. Also, high daytime (MVK + MACR) ∕ isoprene ratios (1.9±0.5) were observed. Based on the observations, we hypothesized that the lower isoprene levels in the study forest might be attributable to a strong AOC in relation to the elevated regional complex air pollution. In further data analyses, high site-level concentrations of daytime OH (7.3±0.5×106 molecules cm−3) and nighttime NO3 radicals (6.0±0.5×108 molecules cm−3) were estimated by using a photochemical box model incorporating the master chemical mechanism (PBM-MCM), and high regional mixing ratios of OH (19.7±2.3×106 molecules cm−3) during 09:00–15:00 LT were also obtained by applying a parameterization method with measured aromatic hydrocarbons. And besides, high initial mixing ratios (1213±108 pptv) and short atmospheric reaction time (0.27 h) of isoprene during the day were derived by a sequential reaction approach. All these indicate that isoprene was rapidly and highly oxidized in this forest, which supports our hypothesis. The study suggests that the complex air pollution in the PRD may have significantly elevated the background AOC of the adjacent forests, and probably affects the regional air quality and ecological environment in the long term. The feedback of forest ecosystems to the increasing AOC in southern China warrants further studies.