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Particulate lead (Pb) is a primary air pollutant that affects society because of its health impacts. This study investigates the source sectors of Pb associated with ambient fine particulate matter (PM2.5) over central-western Taiwan (CWT) with new constraints on the Pb-isotopic composition. We demonstrate that the contribution of coal-fired facilities is overwhelming, which is estimated to reach 35 ± 16% in the summertime and is enhanced to 57 ± 24% during the winter monsoon seasons. Moreover, fossil-fuel vehicles remain a major source of atmospheric Pb, which accounts for 12 ± 5%, despite the current absence of a leaded gasoline supply. Significant seasonal and geographical variations in the Pb-isotopic composition are revealed, which suggest that the impact of East Asian (EA) pollution outflows is important in north CWT and drastically declines toward the south. We estimate the average contribution of EA outflows as accounting for 35 ± 15% (3.6 ± 1.5 ng/m3) of the atmospheric Pb loading in CWT during the winter monsoon seasons.

Particulate lead (Pb) is a primary air pollutant that affects society because of its health impacts. This study investigates the source sectors of Pb associated with ambient fine particulate matter (PM

Fog has drawn much attention from scholars and the public; it can reduce visibility to less than 1 km and affect air, sea, and land transportation and economy. In late winter and spring, fog events frequently affect intensive human activity in the coastal areas of Eastern China. In this study, numerical simulations from the Weather Research and Forecasting model were combined with observations to investigate the effects of aerosol on the microphysical properties of fog over the Taiwan Strait in April from 2015 to 2017. The mean values of observed liquid water content, number concentration of fog droplets, and mean diameter fog droplets were 0.11 g/m3, 2.2 × 108 #/m3, and 13.9 μm. The observed relationships between fog microphysical properties were close to the simulation results in the urban aerosol experiment, suggesting that the fog events at Kinmen were significantly affected by urban aerosols. The simulation results indicated that the wind blew from the south, and the air temperature was about 1°C higher than the sea surface temperature on foggy days. A stable condition accompanied by a shallow planetary boundary layer was favorable to fog formation. In the urban aerosol experiment, higher number density of aerosols resulted in more but smaller droplets and increased the LWC. An increase in aerosols reflected shortwave radiation, resulting in a colder and wetter atmosphere during fog events in the daytime. This led to a thicker fog layer and an increased number of fog droplets in the urban aerosol experiment. Foggy days and microphysical properties at Kinmen significantly differed between the studied years. As suggested by the correlations between fog-day anomalies and the corresponding Nino 3.4 index and Oceanic Nino Index, this interannual difference might be attributable to the 2015 to 2016 El Nino–Southern Oscillation (ENSO). Further observations are required to ascertain the relationship between fog events, fog microphysics, and ENSO events.

The chemical composition of fine particulate matters (PM2.5), the size distribution and number concentration of aerosol particles (NCN) and the number concentration of cloud condensation nuclei (NCCN) were measured at the northern tip of Taiwan Island during a campaign from April 2017 to March 2018. The parameters of aerosol hygroscopicity (i.e. activation ratio, activation diameter and kappa) were retrieved from the measurements. Significant variations were found in the hygroscopicity of aerosols, which were suggested be subject to various pollution sources, including aged air pollutants originating in the eastern/northern China and transported on the Asian continental outflows, fresh particles emitted from local sources and distributed by land-sea breeze circulations as well as produced by new particle formation (NPF) processes. Cluster analysis was applied to the backward trajectories of air masses to investigate their respective source regions. The results showed that the aerosols associated with Asian continental outflows were characterized with higher kappa values, whereas higher NCCN and NCN with lower kappa values were found for aerosols in local air masses. The distinct features in hygroscopicity were consistent with the characteristics in the chemical composition of PM2.5. Moreover, this study revealed that the nucleation mode particles from NPF could have participated in the enhancement of CCN activity, most likely by coagulating with sub-CCN particles, although the freshly produced particles were not favored for CCN activation due to their smaller sizes. Thus, the results of this study suggested that the NPF coupling with coagulation processes can significantly increase the NCCN in atmosphere.

Organonitrates (ONs) are an important component of atmospheric aerosols that signify the perturbation of nitrogen oxides (NOx) pollution in the remote atmosphere. This study investigated the mass concentration and molecular composition of ONs in submicron particulate matters (PM1) at a subtropical forest site (Xitou), which located downwind the Taichung metropolis in the Central Taiwan. Here we showed that transport of urban air pollution with local circulations caused elevation in the ambient concentration of ONs in the forested area. In addition, the levels of ONs were positively correlated with ozone mixing ratio and were negatively correlated with the relative humidity, suggesting that the ONs were regulated by photochemistry and hydrolysis. The results also showed that the mass concentration of the ONs was significantly correlated with the number density of nanoparticles (d

The aim of this study is to investigate the seasonal variations in the physicochemical properties of atmospheric ultra-fine particles (UFPs, d ≤ 100 nm) and submicron particles (PM1, d ≤ 1 µm) in an east Asian urban area, which are hypothesized to be affected by the interchange of summer and winter monsoons. An observation experiment was conducted at TARO (Taipei Aerosol and Radiation Observatory), an urban aerosol station in Taipei, Taiwan, from October 2012 to August 2013. The measurements included the mass concentration and chemical composition of UFPs and PM1, as well as the particle number concentration (PNC) and the particle number size distribution (PSD) with size range of 4–736 nm. The results indicated that the mass concentration of PM1 was elevated during cold seasons with a peak level of 18.5 µg m−3 in spring, whereas the highest concentration of UFPs was measured in summertime with a mean of 1.64 µg m−3. Moreover, chemical analysis revealed that the UFPs and PM1 were characterized by distinct composition; UFPs were composed mostly of organics, whereas ammonium and sulfate were the major constituents of PM1. The seasonal median of total PNCs ranged from 13.9 × 103 cm−3 in autumn to 19.4 × 103 cm−3 in spring. Median concentrations for respective size distribution modes peaked in different seasons. The nucleation-mode PNC (N4 − 25) peaked at 11.6 × 103 cm−3 in winter, whereas the Aitken-mode (N25 − 100) and accumulation-mode (N100 − 736) PNC exhibited summer maxima at 6.0 × 103 and 3.1 × 103 cm−3, respectively. The change in PSD during summertime was attributed to the enhancement in the photochemical production of condensable organic matter that, in turn, contributed to the growth of aerosol particles in the atmosphere. In addition, clear photochemical production of particles was observed, mostly in the summer season, which was characterized by average particle growth and formation rates of 4.0 ± 1.1 nm h−1 and 1.4 ± 0.8 cm−3 s−1, respectively. The prevalence of new particle formation (NPF) in summer was suggested as a result of seasonally enhanced photochemical oxidation of SO2 that contributed to the production of H2SO4, and a low level of PM10 (d ≤ 10 µm) that served as the condensation sink. Regarding the sources of aerosol particles, correlation analysis of the PNCs against NOx revealed that the local vehicular exhaust was the dominant contributor of the UFPs throughout the year. Conversely, the Asian pollution outbreaks had significant influence in the PNC of accumulation-mode particles during the seasons of winter monsoons. The results of this study implied the significance of secondary organic aerosols in the seasonal variations of UFPs and the influences of continental pollution outbreaks in the downwind areas of Asian outflows.

A measurement campaign was conducted from 3 to 19 December 2012 at an urban site of Brisbane, Australia. Size distribution of ions and particle number concentrations were measured to investigate the influence of particle formation and biomass burning on atmospheric ion and particle concentrations. Overall ion and particle number concentrations during the measurement period were found to be (− 1.2 × 10 3 cm − 3 | + 1.6 × 10 3 cm − 3 ) and 4.4 × 10 3 , respectively. The results of correlation analysis between concentrations of ions and nitrogen oxides indicated that positive and negative ions originated from similar sources, and that vehicle exhaust emissions had a more significant influence on intermediate/large ions, while cluster ions rapidly attached to larger particles once emitted into the atmosphere. Diurnal variations in ion concentration suggested the enrichment of intermediate and large ions on new particle formation event days, indicating that they were involved in the particle formation processes. Elevated total ions, particularly larger ions, and particle number concentrations were found during biomass burning episodes. This could be due to the attachment of cluster ions onto accumulation mode particles or production of charged particles from biomass burning, which were in turn transported to the measurement site. The results of this work enhance scientific understanding of the sources of atmospheric ions in an urban environment, as well as their interactions with particles during particle formation processes.

This study demonstrates a novel method for testing the hypothesis that variations in primary and secondary particle number concentration (PNC) in urban air are related to residual fuel oil combustion at a coastal port lying 30 km upwind, by examining the correlation between PNC and airborne particle composition signatures chosen for their sensitivity to the elemental contaminants present in residual fuel oil. Residual fuel oil combustion indicators were chosen by comparing the sensitivity of a range of concentration ratios to airborne emissions originating from the port. The most responsive were combinations of vanadium and sulfur concentration ([S], [V]) expressed as ratios with respect to black carbon concentration ([BC]). These correlated significantly with ship activity at the port and with the fraction of time during which the wind blew from the port. The average [V] when the wind was predominantly from the port was 0.52 ng.m-3 (87%) higher than the average for all wind directions and 0.83 ng.m-3 (280%) higher than that for the lowest vanadium yielding wind direction considered to approximate the natural background. Shipping was found to be the main source of V impacting urban air quality in Brisbane. However, contrary to the stated hypothesis, increases in PNC related measures did not correlate with ship emission indicators or ship traffic. Hence at this site ship emissions were not found to be a major contributor to PNC compared to other fossil fuel combustion sources such as road traffic, airport and refinery emissions.

An intensive aerosol characterization experiment was performed at the Taipei Aerosol and Radiation Observatory (TARO, 25.02° N, 121.53° E) in the urban area of Taipei, Taiwan, during July 2012. Number concentration and size distribution of aerosol particles were measured continuously, which were accompanied by concurrent measurements of mass concentration of submicron particles, PM1 (d ≤ 1 μm), and photolysis rate of ozone, J(O1D). The averaged number concentrations of total (Ntotal), accumulation mode (Nacu), Aitken mode (NAitken), and nucleation mode (Nnuc) particles were 13.9 × 103 cm−3, 1.2 × 103 cm−3, 6.1 × 103 cm−3, and 6.6 × 103 cm−3, respectively. Accordingly, the ultrafine particles (UFPs, d ≤ 100 nm) accounted for 91% of the total number concentration of particles measured in this study (10 ≤ d ≤ 429 nm), indicating the importance of UFPs to the air quality and radiation budget in Taipei and its surrounding areas. An averaged Nnuc / NOx ratio of 192.4 cm−3 ppbv−1 was derived from nighttime measurements, which was suggested to be the characteristic of vehicle emissions that contributed to the "urban background" of nucleation mode particles throughout a day. On the contrary, it was found that the number concentration of nucleation mode particles was independent of NOx and could be elevated up to 10 times of the "urban background" levels during daytime, suggesting a substantial amount of nucleation mode particles produced from photochemical processes. Averages (± 1σ) of the diameter growth rate (GR) and formation rate of nucleation mode particles, J10, were 11.9 ± 10.6 nm h−1 and 6.9 ± 3.0 cm−3 s−1, respectively. Consistency in the time series of the nucleation mode particle concentration and the proxy of H2SO4 production, UVB · SO2/CS, for new particle formation (NPF) events suggested that photooxidation of SO2 was likely one of the major mechanisms for the formation of new particles in our study area. Moreover, it was revealed that the particle growth rate correlated exponentially with the photolysis of ozone, implying that the condensable vapors were produced mostly from photooxidation reactions. In addition, this study also revealed that Nnuc exhibited a quadratic relationship with J10. The quadratic relationship was inferred as a result of aerosol dynamics and featured NPF processes in urban areas.

New particle formation (NPF) studies have been conducted in China since 2004. Formation of new atmospheric aerosol particles has been observed to take place in diverse environments, even under the circumstances of high pre-existing particle loading, challenging the traditional and present understanding of the physicochemical nucleation mechanisms, which have been proposed based on the investigations in clean environments and under laboratory experimental conditions. This paper summarizes the present status and gaps in understanding NPF in China and discusses the main directions opening for future research.

Particle number concentrations and size distributions, visibility and particulate mass concentrations and weather parameters were monitored in Brisbane, Australia, on 23 September 2009, during the passage of a dust storm that originated 1400 km away in the dry continental interior. The dust concentration peaked at about mid-day when the hourly average PM2.5 and PM10 values reached 814 and 6460 μg m−3, respectively, with a sharp drop in atmospheric visibility. A linear regression analysis showed a good correlation between the coefficient of light scattering by particles (Bsp) and both PM10 and PM2.5. The particle number in the size range 0.5–20 μm exhibited a lognormal size distribution with modal and geometrical mean diameters of 1.6 and 1.9 μm, respectively. The modal mass was around 10 μm with less than 10% of the mass carried by particles smaller than 2.5 μm. The PM10 fraction accounted for about 68% of the total mass. By mid-day, as the dust began to increase sharply, the ultrafine particle number concentration fell from about 6 × 103 cm−3 to 3 × 103 cm−3 and then continued to decrease to less than 1 × 103 cm−3 by 14 h, showing a power-law decrease with Bsp with an R2 value of 0.77 (p < 0.01). Ultrafine particle size distributions also showed a significant decrease in number during the dust storm. This is the first scientific study of particle size distributions in an Australian dust storm.

The aim of this study was to characterise the new particle formation events in a subtropical urban environment in the Southern Hemisphere. The study measured the number concentration of particles and its size distribution in Brisbane, Australia during 2009. The variation of particle number concentration and nucleation burst events were characterised as well as the particle growth rate which was first reported in urban environment of Australia. The annual average NUFP, NAitken and NNuc were 9.3×103, 3.7×103 and 5.6×103 cm−3, respectively. Weak seasonal variation in number concentration was observed. Local traffic exhaust emissions were a major contributor of the pollution (NUFP) observed in morning which was dominated by the Aitken mode particles, while particles formed by secondary formation processes contributed to the particle number concentration during afternoon. Overall, 65 nucleation burst events were identified during the study period. Nucleation burst events were classified into two groups, with and without particles growth after the burst of nucleation mode particles observed. The average particle growth rate of the nucleation events was 4.6 nm h−1 (ranged from 1.79–7.78 nm h−1). Case studies of the nucleation burst events were characterised including (i) the nucleation burst with particle growth which is associated with the particle precursor emitted from local traffic exhaust emission, (ii) the nucleation burst without particle growth which is due to the transport of industrial emissions from the coast to Brisbane city or other possible sources with unfavourable conditions which suppressed particle growth and (iii) interplay between the above two cases which demonstrated the impact of the vehicle and industrial emissions on the variation of particle number concentration and its size distribution during the same day.

The aim of this study is to investigate the seasonal variations in the physicochemical properties of atmospheric ultrafine particles (UFPs, d ≤ 100nm) and submicron particles (PM1, d ≤ 1 μm) in an East-Asian urban area, which are hypothesized to be affected by the interchange of summer and winter monsoons. An observation experiment was conducted at the TARO, an urban aerosol station in Taipei, Taiwan, from October 2012 to August 2013. The measurements included the mass concentration and chemical composition of UFPs and PM1, as well as the particle number concentration (PNC) and size distribution (PSD) with size range of 4–736 nm. The results indicate that the mass concentration of PM1 was elevated during cold seasons with peak level of 18.5 μg m-3 in spring, whereas the highest UFPs concentration was measured in summertime with a seasonal mean of 1.62 μg m-3. Moreover, chemical analysis revealed that the UFPs and PM1 were characterized by distinct composition; UFPs were composed mostly of organics, whereas ammonium and sulfate were the major constituents in PM1. The seasonal median of total PNCs ranged from 13.9 × 103 cm-3 in autumn to 19.4 × 103 cm-3 in spring. The PSD information retrieved from the corresponding PNC measurements indicates that the nucleation mode PNC (N4–25) peaked at 11.6 × 103 cm-3 in winter, whereas the Aitken mode (N25–100) and accumulation mode (N100–736) exhibited summer maxima at 6.0 × 103 and 3.1 × 103 cm-3, respectively. The shift in PSD during summertime is attributed to the enhancement in the photochemical production of condensable organic matter that, in turn, contributes to the growth of aerosol particles in the atmosphere. In addition, remarkable photochemical production of particles was observed in spring and summer seasons, which was characterized with averaged particle growth and formation rates of 4.3 ± 0.8 nm h-1 and 1.6 ± 0.8 cm-3 s-1, respectively. The prevalence of new particle formation (NPF) in summer is suggested as a result of seasonally enhanced photochemical oxidation of SO2, which contributes to the production of H2SO4, and low level of PM10 (d ≤ 10 μm) that serves as the condensation sink. Regarding the sources of aerosol particles, correlation analysis upon the PNCs against NOx revealed that the local vehicular exhaust was the dominant contributor of the UFPs throughout a year. On the contrary, the Asian pollution outbreaks can have significant influence in the PNC of accumulation mode particles during the seasons of winter monsoons. The results of this study underline the significance of secondary organic aerosols in the seasonal variations of UFPs and the influences of continental pollution outbreaks in the downwind areas of Asian outflows.

The Pearl River Delta (PRD) is a fast developing region in China that has experienced serious air pollution. In this study, we present the measurement results of fine particulate matter (PM2.5) mass, major ions, and carbonaceous concentrations at a rural site in southern PRD during November to December 2002. The aims of this study are to characterize the temporal variation of PM2.5 mass and chemical composition in winter, which is typically a season of high pollution, and to estimate the contribution of sources from PRD inland and coastal cities (Hong Kong and Shenzhen) on the levels of fine particles observed in the downwind area. The average concentration of 24-h PM2.5 filter samples (N=24) was 41.3 (±17.1) μg m−3 (±standard deviation), with the concentration of individual samples ranging from 10.1 to 89.9 μg m−3. Particulate organic matter (POM) and non-sea-salt sulfate (nss-SO42−) were the major components of PM2.5 accounting for 42% and 25% of the total mass, respectively. Examination of the ratio of secondary organic carbon to total organic carbon suggests that approximately 34% of organic carbon was of secondary origin. The temporal variations of PM2.5 concentrations were strongly influenced by synoptic wind flow. The regional outflows from PRD inland and coastal cities made significant contributions to the ambient concentrations in the study site, which accounted for 48–57% for PM2.5, 66–72% for POM, and 18–20% for nss-SO42−, respectively. An application of a formula developed in the IMPROVE study showed that POM accounted for 44%, 42% and 22% of the light extinction under northeasterly, northerly, and easterly winds, respectively, whereas ammonium sulfate contributed 45%, 47%, and 70%, respectively. This highlights the significance of fine sulfate in visibility impairment in region with humid climates.

In January 2011, Brisbane, Australia, experienced a major river flooding event. We aimed to investigate its effects on air quality and assess the role of prompt cleaning activities in reducing the airborne exposure risk. A comprehensive, multi-parameter indoor and outdoor measurement campaign was conducted in 41 residential houses, 2 and 6 months after the flood. The median indoor air concentrations of supermicrometer particle number (PN), PM10, fungi and bacteria 2 months after the flood were comparable to those previously measured in Brisbane. These were 2.88 p cm−3, 15 μg m−3, 804 cfu m−3 and 177 cfu m−3 for flood-affected houses (AFH), and 2.74 p cm−3, 15 μg m−3, 547 cfu m−3 and 167 cfu m−3 for non-affected houses (NFH), respectively. The I/O (indoor/outdoor) ratios of these pollutants were 1.08, 1.38, 0.74 and 1.76 for AFH and 1.03, 1.32, 0.83 and 2.17 for NFH, respectively. The average of total elements (together with transition metals) in indoor dust was 2296 ± 1328 μg m−2 for AFH and 1454 ± 678 μg m−2 for NFH, respectively. In general, the differences between AFH and NFH were not statistically significant, implying the absence of a measureable effect on air quality from the flood. We postulate that this was due to the very swift and effective cleaning of the flooded houses by 60,000 volunteers. Among the various cleaning methods, the use of both detergent and bleach was the most efficient at controlling indoor bacteria. All cleaning methods were equally effective for indoor fungi. This study provides quantitative evidence of the significant impact of immediate post-flood cleaning on mitigating the effects of flooding on indoor bioaerosol contamination and other pollutants. Keywords: Indoor air, Particle number, PM10, Fungi, Bacteria, Indoor dust

Elevated particle number concentration (PNC) observed during nucleation events could make a significant contribution to the total particle load and thus air pollution in urban environments. Therefore, a field measurement study of PNC was conducted to investigate the temporal and spatial variations of PNC within the urban airshed of Brisbane, Australia. PNC was monitored at urban (QUT), roadside (WOO) and semi-urban (ROC) areas around the Brisbane region during 2009. The results showed that morning traffic exhaust emissions were the main contributor to high PNCs at QUT and WOO which contributed 5.5% and 5.1 5 during the week, respectively, with a less significant contribution on weekends. PNC peaks were observed around noon, which correlated with the highest solar radiation levels at all three stations, thus suggesting that high PNC levels were likely to be associated with new particle formation caused by photochemical reactions. Wind rose plots showed relatively higher PNC for the NE direction, which was associated with industrial pollution, accounting for 12%, 9% and 14% of overall PNC at QUT, WOO and ROC, respectively. Although there was no significant correlation between PNC at each station, the variation of PNC was well correlated among three stations during regional nucleation events. In addition, PNC at ROC was significantly influenced by upwind urban pollution during the nucleation burst events, with the average enrichment factor of 15.4. This study provides an insight into the influence of regional nucleation events on PNC in the Brisbane region and is the first study to quantify the effect of urban pollution on semi-urban PNC through the nucleation events.

The aim of this work was to review the existing instrumental methods to monitor airborne nanoparticles in different types of indoor and outdoor environments in order to detect their presence and to characterise their properties. Firstly the terminology and definitions used in this field are discussed, which is followed by a review of the methods to measure particle physical characteristics including number, concentration, size distribution and surface area. An extensive discussion is provided on the direct methods for particle elemental composition measurements, as well as on indirect methods providing information on particle volatility and solubility, and thus in turn on volatile and semivolatile compounds of which the particle is composed. A brief summary of broader considerations related to nanoparticle monitoring in different environments concludes the paper.