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Fine urban aerosol particles with aerodynamic equivalent dimeter ≤2.5 μm (PM 2.5 ) were collected in Mainz (a city within the Rhine-Main area, the third largest metropolitan region in Germany) and Beijing (Chinese megacity). A solvent mixture of acetonitrile-water was used to extract the organic aerosol fraction (OA) from the particle samples. The extracts were analyzed by an ultrahigh resolution mass spectrometer (UHRMS) Orbitrap coupled with ultra-high-performance liquid chromatography (UHPLC) both in the negative and positive ion mode. The number of compounds observed in Beijing is a factor of 2–10 higher compared to Mainz. The clear differences on chemical composition of OA in the two cities were observed. The majority of organics in Beijing OA is characterized by lower elemental H/C and O/C ratio but a higher degree of unsaturation and a larger aromaticity equivalent (X C ) compared to Mainz OA, suggesting that aromatics, which are related to direct combustion compounds (e.g., oxidized polycyclic aromatic hydrocarbon (PAH)), play an important role for OA in Beijing. A significant number of organosulfates (OSs) with long-carbon chain and low degree of unsaturation were observed in Beijing OA, indicating that long-chain alkanes emitted by vehicle might be their precursors. [ABSTRACT FROM AUTHOR]

Aerosol size distributions were measured using a scanning mobility particle sizer (SMPS), and also PM 1 (particulate matter ≤ 1 μm in aerodynamic diameter) samples were collected in parallel at a representative site in New Delhi during spring in 2013 and 2014. Based on the temporal variation of particle count mean diameter (CMD), sampling periods are characterized as growth events and non-growth events. Particle size distribution measurements suggest that some consecutive nights experienced unique nighttime subsequent growth of particles, which sustained for a longer period. Average particle growth rate measured during growth events was 5.64 ± 3.03 nm h −1 . Atmospheric trace gas concentrations and meteorological data show that these growth events (nighttime) are influenced by higher concentrations of gases, e.g., NO 2 (56.5 ± 29.7 μg m −3 ), SO 2 (9.34 ± 1.14 μg m −3 ) and RH (45.7 ± 9.5%) than those of non-growth events (daytime) (37.9 ± 18.6 μg m −3 , 7.19 ± 2.08 μg m −3 and 37.7 ± 6.9%, respectively). Further, analysis of PM 1 samples collected during the study period shows that the particulate water-soluble organic carbon (WSOC) (12.7 ± 4.1 μg m −3 ), NH 4 + (9.4 ± 3.2 μg m −3 ), SO 4 2− (2.03 ± 0.70 μg m −3 ), K + (1.06 ± 0.40 μg m −3 ), and NO 2 − + NO 3 − (0.59 ± 0.36 μg m −3 ) are the major contributors of particulate mass, wherein NH 4 + , SO 4 2− , K + , NO 2 − + NO 3 − mass concentrations were higher during growth events. Correlation study shows that nighttime aerosol composition during growth (in sub-micron range) events are more enriched by inorganic species (i.e., NH 4 NO 3 , (NH 4 ) 2 SO 4 and H 2 SO 4 vapors) as compared to organics (i.e., WSOC, does not show much difference in growth events and non events). Our results suggest that nighttime sulfate formation at the site is mostly mediated by high NO 2 and NH 3 at elevated RH. For the formation of sulfate and other inorganic species, a nighttime atmospheric chemistry is proposed, which is linked to particle growth. Growth events observed typically in nighttime have both biomass burning and anthropogenic influences as indicated by high concentrations of WSOC, K + and black carbon in PM 1 and carbon monoxide in gas phase. [ABSTRACT FROM AUTHOR]

Atmospheric ammonia plays an important role in haze formation in East China. In this study, long-term measurements of NH 3 concentrations were implemented at urban, suburban, and tunnel sites in Shanghai, the largest city in East China. The average monthly ammonia concentrations at the urban site varied from 3.7 ppb to 14.5 ppb and exhibited the highest levels in summer and lowest levels in winter, indicating that the biological emissions and agriculture in the surrounding areas are important contributors. The suburban NH 3 levels were significantly higher in autumn compared to those at the urban site, indicating the important contribution of agricultural activities. Regardless of the season, the difference of NH 3 concentrations between the tunnel and urban sites remained almost constant. On average, the tunnel NH 3 level was three times higher than that of the nearby urban site, indicating strong vehicle NH 3 emissions in the tunnel. The tunnel NH 3 levels on weekdays were comparable to those on weekends, a result that was in agreement with the daily average traffic volume. It was estimated that the vehicle emissions contributed 12.6–24.6% of the atmospheric NH 3 in the urban area and 3.8–7.5% for the whole area of Shanghai. Our results suggest that vehicle NH 3 emissions should be considered, although agricultural emissions are still more important for mitigating severe haze pollution during wintertime in the megacities of China. [ABSTRACT FROM AUTHOR]

This study presents the technology based emission factors of gaseous pollutants (CO, CO 2 , and NO X ) measured during on-road operation of nine passenger cars of diesel, gasoline, and compressed natural gas (CNG). The emissions from two 3-wheelers, and three 2-wheelers were measured by putting the vehicles on jacks and operating them according to Modified Indian Driving Cycle (MIDC) at no load condition. The emission factors observed in the present work were significantly higher than values reported from dynamometer study by Automotive Research Association of India (ARAI). Low CO (0.34 ± 0.08 g km −1 ) and high NO X (1.0 ± 0.4 g km −1 ) emission factors were observed for diesel passenger cars, oppositely high CO (2.2 ± 2.6 g km −1 ) and low NO X (1.0 ± 1.6 g km −1 ) emission factors were seen for gasoline powered cars. The after-treatment technology in diesel vehicles was effective in CO reduction. While the use of turbocharger in diesel vehicles to generate high combustion temperature and pressure produces more NOx, probably which may not be effectively controlled by after-treatment device. The after-treatment devices in gasoline powered Post-2010, Post-2005 vehicles can be acclaimed for reduced CO emissions compared to Post-2000 vehicles. This work presents a limited data set of emission factors from on-road operations of light duty vehicles, this limitation can be improved by further measurements of emissions from similar vehicles. [ABSTRACT FROM AUTHOR]

Particulate pollution has remained at a high level in the megacity of Beijing in the past decade. The PM2.5, PM10, aerosol optical depth (AOD), Angstrom exponent(α), and PM2.5/PM10 ratio (the proportion of PM2.5 in PM10) in Beijing were 70±6 μg m −3 , 128±6 μg m −3 , 0.57 ± 0.05, 1.10 ± 0.08, 45 ± 4%, respectively, from 2005 to 2014. The annual means of PM concentration, AOD, α, and PM2.5/PM10 ratio decreased slightly during this decade, meanwhile PM concentration increased in the winter. Furthermore, we found there were thresholds of PM2.5 concentration for aerosol extinction. When the PM concentration was lower than a certain threshold, AOD decreased quickly with the decline of PM concentration. To make the improvement of the particle pollution more noticeable, the PM concentration should be controlled under the threshold. The annual averaged threshold is 63 μg m −3 , and the threshold values reached the maximum of 74 μg m −3 in spring, ranged from 54 to 56 μg m −3 in the three other seasons. The threshold values ranged from 55 to 77 μg m −3 under other relevant factors, including air masses directions and relative humidity. [ABSTRACT FROM AUTHOR]

Water-soluble organic carbon (WSOC) is a significant part of ambient aerosol and plays an active role in contributing to aerosol's effect on visibility degradation and radiation budget through its interactions with atmospheric water. Size-segregated aerosol samples in the range of 0.056–18 μm were collected using a ten-stage impactor sampler at an urban site in Hong Kong over one-year period. The WSOC samples were separated into hydrophilic (termed WSOC_h) and hydrophobic fractions (i.e., the humic-like substances (HULIS) fraction) through solid-phase extraction procedure. Carbon in HULIS accounted for 40 ± 14% of WSOC. The size distribution of HULIS was consistently characterized in all seasons with a dominant droplet mode (46–71%) and minor condensation (9.0–18%) and coarse modes (20–35%). The droplet mode had a mass median aerodynamic diameter in the range of 0.7–0.8 μm. This size mode showed the largest seasonal variation in abundance, lowest in the summer (0.41 μg/m 3 ) and highest in the winter (3.3 μg/m 3 ). WSOC_h also had a dominant droplet mode, but was more evenly distributed among different size modes. Inter-species correlations within the same size mode suggest that the condensation-mode HULIS was partly associated with combustion sources and the droplet-mode was strongly associated with secondary sulfate formation and biomass burning particle aging processes. There is evidence to suggest that the coarse-mode HULIS largely originated from coagulation of condensation-mode HULIS with coarse soil/sea salt particles. The formation process and possible sources of WSOC_h was more complicated and multiple than HULIS and need further investigation. Our measurements indicate that WSOC components contributed a dominant fraction of water-soluble aerosol mass in particles smaller than 0.32 μm while roughly 20–30% in the larger particles. [ABSTRACT FROM AUTHOR]

Aerosol properties derived from sun-photometric observations at Wuhan during a haze period were analyzed and used as input in a radiative transfer model to calculate the aerosol radiative effect (ARE) in ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) spectra. The results showed that the aerosol optical depth (AOD) at 440 nm increased from 0.32 under clear-air conditions to 0.85 during common haze and 1.39 during severe haze. An unusual inverse relationship was found between the Ångström exponent (AE) and AOD during the haze period at Wuhan. Under high-humidity conditions, the fine-mode median radius of aerosols increased from 0.113 μm to approximately 0.2–0.5 μm as a result of hygroscopic growth, which led to increases in the AOD and decreases in the AE simultaneously. These changes were responsible for the inverse relationship between AE and AOD at Wuhan. The surface ARE in the UV (ARE UV ), VIS (ARE VIS ), NIR (ARE NIR ), and SW (ARE SW ) spectra changed from −4.46, −25.37, −12.15, and −41.99 W/m 2 under clear-air conditions to −9.48, −53.96, −29.81, and −93.25 W/m 2 during common hazy days and −12.89, −80.16, −55.17, and −148.22 W/m 2 during severe hazy days, respectively, and the percentages of ARE UV , ARE VIS , and ARE NIR in ARE SW changed from 11%, 61%, and 28%–9%, 54%, and 37%, respectively. Meanwhile, the ARE efficiencies (REE) in SW varied from −206.5 W/m 2 under clear-air conditions to −152.94 W/m 2 during the common haze period and −131.47 W/m 2 during the severe haze period. The smallest decreasing rate of the REE in NIR was associated with the increase of ARE NIR . The weakened REE values were related to the strong forward scattering and weak backward scattering of fine aerosol particles with increasing size resulting from hygroscopic growth, while the variation of the single scattering albedo showed less impact. Source region analysis by back trajectories and the concentration weighted trajectory (CWT) method showed that black carbon came from nearby regions with low trajectories, and the surrounding haze areas were major sources of fine-mode particles in the haze in Wuhan. [ABSTRACT FROM AUTHOR]

Peroxyacyl nitrates (PANs) are photochemical secondary pollutants that play a key role in the atmospheric chemistry of the troposphere. However, there have been few studies on the long-term variation and inter-regional transport of PANs. In this study, summertime ambient PAN concentrations were monitored at urban and rural sites in Beijing and Hebei, China, between 2006 and 2014. In Beijing, the peak concentrations of PAN and PPN were in the range of 6–17 ppbv and 0.6–2.2 ppbv, respectively, higher than concentrations in other provinces. The nitrogen oxide (NO x ) concentration decreased at a rate of 1.7 ppbv/yr (∼4% yr −1 ), and the PAN concentration decreased at a rate of 0.03 ppbv/yr (∼3% yr −1 ), while the ozone (O 3 ) concentration increased at a rate of 1.5 ppbv/yr (∼4% yr −1 ). Trajectory clustering analyses showed that high concentrations of PAN were mainly affected by low air masses transported medium/short distances from South Beijing, and the potential source contribution function maps showed that the likely pollution source area was concentrated in the southern region of Beijing. These findings provide a theoretical basis for pollution control in this region. [ABSTRACT FROM AUTHOR]

This research determined intake dose of fine particulate matter (PM 2.5 ), equivalent black carbon ( e BC ), and number of sub-micron particles ( N p ) for commuters in Bogotá, Colombia. Doses were estimated through measurements of exposure concentration, a surrogate of physical activity, as well as travel times and speeds. Impacts of travel mode, traffic load, and street configuration on dose and exposure were explored. Three road segments were selected because of their different traffic loads and composition, and dissimilar street configuration. The transport modes considered include active modes (walking and cycling) and motorized modes (bus, car, taxi, and motorcycle). Measurements were performed simultaneously in the available modes at each road segment. High average e BC concentrations were observed throughout the campaign, ranging from 20 to 120 μ g m − 3 . Commuters in motorized modes experienced significantly higher exposure concentrations than pedestrians and bicyclists. The highest average concentrations of PM 2.5 , e BC , and N p were measured inside the city's Bus Rapid Transit (BRT) system vehicles. Pedestrians and bicycle users in an open street configuration were exposed to the lowest average concentrations of PM 2.5 and e BC , six times lower than those experienced by commuters using the BRT in the same street segment. Pedestrians experienced the highest particulate matter intake dose in the road segments studied, despite being exposed to lower concentrations than commuters in motorized modes. Average potential dose of PM 2.5 and e BC per unit length traveled were nearly three times higher for pedestrians in a street canyon configuration compared to commuters in public transport. Slower travel speed and elevated inhalation rates dominate PM dose for pedestrians. The presence of dedicated bike lanes on sidewalks has a significant impact on reducing the exposure concentration for bicyclists compared to those riding in mixed traffic lanes. This study proposes a simple method to perform loading effect correction for measurements of black carbon using multiple portable aethalometers. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of the temporary strengthening of air quality assurance controlling measures during the Beijing 2015 IAAF World Championships and the Military Parade Assurance Period (MPAP) in China, we collected daily PM 2.5 aerosol samples at three typical sites (urban downtown, suburban and rural background area, respectively) in Beijing and investigated the variations of concentration of the water-soluble ions, elemental constituents, organic carbon (OC) and elemental carbon (EC) in PM 2.5 from Aug.15 to Sept.10, 2015. Simultaneously, 1-h high-resolution continuous monitoring results of PM 2.5 mass concentration as well as the chemical components which were measured at another online monitoring urban site were incorporated. The concentrations of PM 2.5 and other gaseous pollutants (SO 2 , NO 2 and CO) during the parade control period (Aug.20-Sept.3) exhibited a substantially decrease compared with the concentrations during both the non-control (August 15 to August 19 and September 4 to September 10) period and the same period in 2014. According to the CMC results, the major components were identified as secondary inorganic aerosol (SIA, the combination of sulfate, ammonium and nitrate), mineral dust and particular organic matter (POM), which together accounted for more than 80% of PM 2.5 in urban and suburban sites. POM is found to account for the largest proportion, and the obviously higher proportion of POM in the urban area revealed the significance contribution from vehicles. Compared with the non-control period, the mass concentrations of SIA and secondary organic carbon (SOC) decreased obviously. However, SIA and SOC are observed to play an important role in contributing to the rapid growth process of PM 2.5 under unfavorable meteorological conditions during the control period. In view of the gradual improvement of air quality in Beijing, as well as the contribution of secondary aerosol formations in total PM 2.5 , effective control of primary gaseous pollutants and volatile organic compounds (VOCs) will be very significant for further lowering the concentration of PM 2.5 in Beijing in normal time. [ABSTRACT FROM AUTHOR]

In this study, 52 paired gas and particle samples were collected from a suburban field in Guangzhou in 2012 using a high-volume active air sampler; they were then analysed for 30 polychlorinated biphenyl (PCB) congeners via gas chromatography with tandem mass spectrometry. Total PCB concentrations ranged from 97.4 to 853 pg m −3 . This was a moderate level compared with other cities, undeveloped areas, and electronic waste disposal sites. Atmospheric concentrations of PCBs did not exhibit notable diurnal or seasonal variations, except for a few high measurement. Tetra- and tri-CBs were the predominant PCB compounds, with an average combined contribution of 81.9%. CB-77 was the dominant congener in the particle phase due to a few samples with extremely high mass fraction of CB-77 and relatively low concentrations of other PCBs. Based on measurements of pollution characteristics including diurnal and seasonal variations, we used correlation analysis, principal component analysis and back trajectory modeling to deduce that electronic manufacturing and recycling activities, pigment/paint production, and waste incineration plants are possible sources of PCBs in Guangzhou. Of these sources, the high observed contributions of CB-77 originated mainly from the pigment/paint industry. [ABSTRACT FROM AUTHOR]

A vehicle fleet representative of passenger vehicles driven in the Seoul Metropolitan Region was investigated for primary emissions and secondary chemistry. Exhaust was photochemically oxidized in a flow reactor to determine the ammonium nitrate (NH 4 NO 3 ) aerosol formation potential from vehicles of gasoline, diesel and liquid petroleum gasoline (LPG) fuel types. Secondary formation of aerosol NH 4 NO 3 , was larger than primary emissions for all vehicle fuel types except diesel, for which negligible secondary NH 4 NO 3 production was observed. Although diesel vehicles emitted more primary nitrogen oxides than other vehicle types, ammonia emitted from gasoline and liquid petroleum gasoline fuels types limited the secondary production of NH 4 NO 3 . The results suggest that gasoline and liquid petroleum gasoline vehicles with three-way catalysts could be an important source of ammonia for NH 4 NO 3 aerosol formation in ammonia-limited environments, including the Seoul Metropolitan Region. [ABSTRACT FROM AUTHOR]

To investigate on the daytime OH and its implication to fine particle, the long-path differential optical absorption spectroscopy (LP-DOAS) system was employed to observe the main OH precursors of O 3 , HCHO and HONO, as well as NO 2 and NO 3 radical from April to August 2013 over Shanghai, China. The main OH production paths from HONO, HCHO and O 3 were estimated to be occupied around 57.6%, 30.5% and 11.9% during daytime. The daytime OH radical concentration under steady-state was averaged at 1.02 × 10 7 molec cm −3 , which was significantly impacted by the photolytic processes. The relationship between photolysis frequency j(O 1 D) and OH radical suggests that heavy fine particle loads can make the photolytic reactions less efficiently and decrease the OH production and concentration. Utilizing CO as the indicator, the part of PM 2.5 mass related to primary emitted sources was found less impacted by the OH levels. The contribution of secondary organic aerosol with metrics of O 3 was enhanced with the increases of the OH levels, while secondary inorganic part of PM 2.5 was favor of the condition that smaller OH concentrations that 5 × 10 5 –5 × 10 6 molec cm −3 . Meantime, a simplified multivariate model was employed to evaluate the influences of OH levels on different parts of fine particles related to different emission and sources. Normalized by solar radiation, this part of OH unrelated to radiation was found to be inversely related to the PM 2.5 , which indicates the self-cleansing capability of the atmosphere. [ABSTRACT FROM AUTHOR]

Model-measurement comparisons for surface ozone often show significant error, which could be attributed to problems in meteorology and emissions fields. A WRF-SMOKE-CMAQ air quality modeling system was used to investigate the contributions of these inputs. In this space, a base WRF run (BASE) and a WRF run initializing with NOAA GOES satellite sea surface temperature (SST) (SENS) were performed to clarify the impact of high-resolution SST on simulated surface ozone (O 3 ) over the Greater Houston area during 25 September 2013, corresponding to the high O 3 episode during the NASA DISCOVER-AQ Texas campaign. The SENS case showed reduced land-sea thermal contrast during early morning hours due to 1–2 °C lower SST over water bodies. The lowered SST reduced the model wind speed and slowed the dilution rate. These changes led to a simulated downwind O 3 change of ∼5 ppb near the area over land with peak simulated afternoon O 3 . However, the SENS case still under-predicted surface O 3 in urban and industrial areas. Episodic flare emissions, dry sunny postfrontal stagnated conditions, and land-bay/sea breeze transitions could be the potential causes of the high O 3 . In order to investigate the additional sources of error, three sensitivity simulations were performed for the high ozone time period. These involved adjusted emissions, adjusted wind fields, and both adjusted emissions and winds. These scenarios were superimposed on the updated SST (SENS) case. Adjusting NO x and VOC emissions using simulated/observed ratios improved correlation and index of agreement (IOA) for NO x from 0.48 and 0.55 to 0.81 and 0.88 respectively, but still reported spatial misalignment of afternoon O 3 hotspots. Adjusting wind fields to represent morning weak westerly winds and afternoon converging zone significantly mitigated under-estimation of the observed O 3 peak. For example, simulations with adjusted wind fields and adjusted (emissions + wind fields) reduced under-estimation of the peak magnitude of 100 ppb from 50 ppb to 7 and 9 ppb. Additionally, these sensitivity cases captured the timing and location of the observed O 3 hotspots. The simulation case with both adjusted emissions and wind fields showed the best statistics for NO x (correlation: 0.84; IOA: 0.90) and O 3 (correlation: 0.87; IOA: 0.92). These comparisons suggest that emissions and wind fields are important in determining the magnitude of high peaks, and wind direction is more critical in determining their timing and location. Particularly, improving the model capability to reproduce small-scale meteorological conditions favoring O 3 production, such as stagnation and wind reversal, is crucial for accurate placement of locations of peak O 3 and its precursors. [ABSTRACT FROM AUTHOR]

Various epidemiological studies conducted in different parts of the world have conclusively established that the adverse health effects are associated with common urban air pollutants. Although several recent studies revealed the poor air quality status in Delhi, but limited evidence of the impact of criterion air pollutants on human health remains a big limitation for relevant policy changes. So we conducted a time series to estimate the short term effects of ambient air pollution on all-natural-cause mortality in Delhi for the period 2008 to 2010. The study examined the impact of criteria air pollutants [particulate matter less than 10 μm in diameter (PM 10 ), sulphur di-oxide (SO 2 ), Nitrogen di-oxide (NO 2 ), Carbon monoxide (CO) and Ozone (O 3 )] on daily all-cause-mortality rate. A semi-parametric regression model was developed to estimate the short term effects of air pollutants on daily all-natural-cause-mortality adjusting nonlinear confounding of time, temperature and relative humidity. A significant association of all-natural-cause mortality in association with short-term exposure to particulate as well as the gaseous pollutants were observed. The study estimated 0.14% (95% CI 0.02%–0.26%) increase in all-cause-mortality for every 10 μg/m 3 increase in PM 10 concentration. Among the gaseous pollutants, NO 2 has been found to show most significant positive association of 1.00% (95% CI 0.07%–1.93%) increase in all-cause-mortality with every 10 μg/m 3 increase in daily NO 2 concentration. The effect of O 3 and CO has been observed to be significant after controlling the effects of NO 2 . Analysis by different age groups reveals that particulate matter has maximum effect estimate in the age group ≥65 years (RR 1.002, 95% CI 1.000 to 1.004) whereas gaseous pollutants have been found to exhibit maximum effect estimate (RR 1.016, 95% CI 1.002 to 1.030) in the age group 5–44 years. The results of the present effect estimates appeared consistent with previous findings and can enhance the strength of the previous evidences to understand health burden associated with local air quality. [ABSTRACT FROM AUTHOR]

Background Global temperature and the frequency of extreme weather events are projected to increase and affect indoor exposure to outdoor particulate matter (PM); however, no studies have quantitatively examined the effect of climate change on particle infiltration and indoor PM exposure. Obective To quantify the relationship between future changes in ambient temperature and fine particle (PM 2.5 ) infiltration in the Greater Boston area. Methods We assembled a large database of outdoor and indoor PM 2.5 data from 340 homes, and used the indoor-outdoor sulfur ratio ( S r ) as a surrogate for PM 2.5 infiltration. We employed linear mixed-effects models to examine the relationship between S r and ambient temperature for all homes in the database and a subgroup of naturally ventilated homes. We used projected temperature data from 1981 to 2000 and 2046–2065 to predict future changes in S r . Results The summer-winter difference in S r was calculated to be 30% and 54% for all homes and in the naturally ventilated subgroup, respectively. The largest future difference in S r (21%) was linked to differences in prevalence of air conditioning. Furthermore, S r was predicted to increase by 7% for naturally ventilated homes and 2% for all homes in summer, corresponding to an average increase of 2–3 °C in future temperature. Conclusions We found that increases in future temperature due to climate change will be associated with increased PM 2.5 infiltration, particularly in summer. The predicted temperature-related changes in S r can be used to characterize future health risk due to elevated indoor PM 2.5 exposure through increased particle infiltration. [ABSTRACT FROM AUTHOR]

The PM 2.5 problem is proving to be a major public crisis and is of great public-concern requiring an urgent response. Information about, and prediction of PM 2.5 from the perspective of atmospheric dynamic theory is still limited due to the complexity of the formation and development of PM 2.5 . In this paper, we attempted to realize the relevance analysis and short-term prediction of PM 2.5 concentrations in Beijing, China, using multi-source data mining. A correlation analysis model of PM 2.5 to physical data (meteorological data, including regional average rainfall, daily mean temperature, average relative humidity, average wind speed, maximum wind speed, and other pollutant concentration data, including CO, NO 2 , SO 2 , PM 10 ) and social media data (microblog data) was proposed, based on the Multivariate Statistical Analysis method. The study found that during these factors, the value of average wind speed, the concentrations of CO, NO 2 , PM 10 , and the daily number of microblog entries with key words ‘Beijing; Air pollution’ show high mathematical correlation with PM 2.5 concentrations. The correlation analysis was further studied based on a big data's machine learning model- Back Propagation Neural Network (hereinafter referred to as BPNN) model. It was found that the BPNN method performs better in correlation mining. Finally, an Autoregressive Integrated Moving Average (hereinafter referred to as ARIMA) Time Series model was applied in this paper to explore the prediction of PM 2.5 in the short-term time series. The predicted results were in good agreement with the observed data. This study is useful for helping realize real-time monitoring, analysis and pre-warning of PM 2.5 and it also helps to broaden the application of big data and the multi-source data mining methods. [ABSTRACT FROM AUTHOR]

It is important to estimate the effects of the long-range transport of atmospheric pollutants for efficient and effective strategies to control air quality. In this study, the contributions of trans-boundary transport to the mean concentrations of SO 2 , NO 2 , CO, and PM 10 in Seoul, Korea from 2001 to 2014 were estimated based on the conditional potential source contribution function (CPSCF) method. Eastern China was found to be the major source of trans-boundary pollution in Seoul, but moderate sources were also located in northeastern China. The contribution of long-range transport from Japan was negligible. The spatial distributions of the potential source contribution function (PSCF) values of each pollutant showed reasonable consistency with their emission inventory and satellite products. The PSCF values of SO 2 and PM 10 from eastern China were higher than those of NO 2 and CO. The mean concentrations of SO 2 , NO 2 , CO, and PM 10 in Seoul for the period from 2001 to 2014 were 5.34, 37.0, and 619.1 ppb, and 57.4 4 μg/m 3 , respectively. The contributions of long-range transport to the mean concentrations of SO 2 , NO 2 , CO, and PM 10 in Seoul were 0.74, 3.4, and 39.0 ppb, and 12.1 μg/m 3 , respectively, which are 14%, 9%, 6%, and 21% of the mean concentrations, respectively. The annual mean concentrations of SO 2 and NO 2 followed statistically significant increasing linear trends (0.5 and 1.6 ppb per decade, respectively), whereas the trends in the annual mean concentrations of CO and PM 10 were statistically insignificant. The trends in the ratio of the increased concentrations associated with long-range transport to the annual mean concentrations of the pollutants were statistically insignificant. However, the results indicate that the trans-boundary transport of SO 2 , NO 2 , CO, and PM 10 from eastern China consistently affected air quality in Seoul over the study period (2001–2014). Regionally, the effects of the long-range transport of pollutants from Beijing and Harbin-Changchun on air quality in Seoul have become more significant over this period. [ABSTRACT FROM AUTHOR]

Characterisation of the effects of varying atmospheric mixing states (stability) in urban climate studies has historically been hampered by problems associated with the complexity of the urban environment, representativity of measurement techniques, and the logistical and financial burdens of maintaining multiple long-term comprehensive measurement sites. These shortcomings, together with a lack of a consistent measurement approach, have limited our ability to understand the physical processes contributing to the urban heat island effect. In this study, we analyse 4 years of continuous hourly near-surface meteorological and atmospheric radon data from an urban–rural site pair in central Poland. A recently-developed radon-based stability classification technique, previously developed for urban pollution characterisation, is employed to characterise the Urban Heat Island Intensity (UHII) and other climatic factors over the full diurnal cycle by season and atmospheric mixing state. By characterising the UHII over a range of atmospheric mixing states in a statistically robust way, this technique provides an effective tool for assessing the efficacy of mitigation measures for urban climate effects in a consistent way over timescales of years to decades. The consistency of approach, ease of application, and unprecedented clarity of findings, provide a strong argument for atmospheric radon observations to be included as part of the ‘standard measurement suite’ for urban climate monitoring networks for non-coastal cities. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) were studied in dry and wet deposition samples collected at urban and suburban sites of Shanghai, China from April 2014 to April 2015. Average wet deposition fluxes of PAHs were higher than dry deposition (62.6 ± 41.5 vs. 26.9 ± 14.4 μg/m 2 /day). However, dry deposition removed more PAHs than wet deposition (69% vs. 31%) due to much shorter durations of wet deposition. The highest dry and wet deposition fluxes were in fall and winter, respectively. The highest amount of dry deposition was in fall and the highest of wet deposition was in summer. The contribution of wet deposition to total deposited PAHs in Shanghai, East China was higher than that in northern China and lower than that in southern China. The difference can be explained by both precipitation amount and removal efficiency (washout ratio). Average dry deposition velocity and washout ratio of particle-associated PAHs were 5.2 cm/s and 5.8 × 10 4 , respectively. Four sources of deposited PAHs were unraveled by positive matrix factorization (PMF) model: traffic, coal combustion, coking and volatilization, contributing 28.7%, 24.6%, 23.7% and 23.0%, respectively. More contribution of traffic and less coal combustion and volatilization were found at urban than at suburban site. As the connection between aerosol and surface soil, deposition had a different PAH composition from those in the two sides, containing more low MW PAHs. That arose the concern that dry deposition velocity and particle washout ratio could be overestimated if coarse particulate matter was excluded from the calculation. Although deposition has been considered as the predominant pathway of PAHs to urban surface system, the PAH composition in street dust differed drastically from that in deposition. This indicated that other sources (e.g. traffic) in urban system could have a greater contribution to PAHs than it had been identified in deposition samples. [ABSTRACT FROM AUTHOR]

São Paulo Megacity (MASP), with more than 20 million inhabitants, is among the world's most populous cities. Brazil is the only area in the world where fuel with a high ethanol content has been used since 1975 and its usage have increased in the last decade with the development of flex-fuel vehicles. Here, the biofuel effect on VOCs burden and composition it is discussed by a crossed analysis of long-term ambient data and emission data over the last decades in MASP. The most abundant NMHCs in ppb v were propane (5.02 ± 5.94), ethylene (3.97 ± 4.55), ethane (2.28 ± 1.89), acetylene (1.98 ± 2.11), 2,2,4-trymethylpentane (2.05 ± 1.48), i-propylbenzene (1.96 ± 1.85), n-butane (1.97 ± 2.24), toluene (1.62 ± 2.02), i-pentane (1.30 ± 1.61) and propylene (1.26 ± 1.54). The comparison with studies performed in MASP over the last 15 years showed a decrease in the NMHC concentration levels, in spite of the growth of the vehicular fleet and fuel consumption. Nevertheless, NMHCs mean concentrations were higher in MASP compared to those in other megacities worldwide (Beijing, London, Los Angeles and Paris) by a factor of 1.1 to 10, although showing similar composition. This suggests that NMHC distribution is dominated by traffic emissions regardless of regional characteristics like fuel usage and composition. Diurnal profiles of NMHC in MASP confirm these findings by all showing the same patterns as CO and acetylene, both recognized as combustion emission tracers. Finally large-scale ethanol usage would not affect the distribution of NMHCs in MASP and gasoline vehicular emissions seem to be the most important source of hydrocarbons in urban areas. [ABSTRACT FROM AUTHOR]

Air pollution is attributable to 7 million deaths per year, or one out of every eight deaths globally. In particular, high concentrations of particulate matter (PM), a major air pollutant, have significant impacts on health and regional climate in urban centers. Many of the most polluted places, largely in developing countries, go severely understudied. Additionally, high particulate matter levels can have an impact on the microphysical properties of clouds, impacting precipitation and regional climate. Semi-arid regions can be especially affected by small changes in precipitation. Here we characterize the physical and chemical properties of PM in one of the most PM-polluted cities in the world: Ulaanbaatar, Mongolia, a semi-arid region in central Asia. Twice monthly aerosol samples were collected over 10 months from a central location and analyzed for composition and ice nucleation activity. Almost all particles collected were inhalable, consisting primarily of mineral dust, soot, and sulfate-organic. In winter, all classes of PM increase in concentration, with increased sulfur concentrations, and the particles are less active towards heterogeneous ice nucleation. In addition, concurrent monthly average PM10, SO 2 , NO x , and O 3 levels and meteorological data at a nearby location are reported and made publicly available. These measurements provide an unprecedented seasonal characterization of the size, shape, chemical structure, and ice nucleating activity of PM data from Ulaanbaatar. This 10-month field study, exploring a variety of aerosol properties in Ulaanbaatar, Mongolia, is one of very few such studies conducted in the region or in such a highly polluted environment. The results of this study may inform work done in other similarly situated and polluted cities in Asia and elsewhere. [ABSTRACT FROM AUTHOR]

Gaining knowledge on the process of particle resuspension from urban paved roads is of particular importance considering the increasing relevance of this source in urban air quality management and the lack of basic information on emission factors and source contributions. In this study we performed extensive field measurements for the quantification of the emission factors from different types of road in the city of Paris, and investigated the causes of their variability and the contributions to the ambient air PM10 observed across one year at one traffic monitoring site in the ring road of Paris. Results show agreement between lower road dust loadings (RD10: 0.7–2.2 mg m −2 ) and emission factors (5.4–9.0 mg vehicle −1 km −1 ) at inner-roads of Paris, compared to the ring road (2.4 mg m −2 and 17 mg vehicle −1 km −1 , respectively), where the two parameters are estimated independently. The higher values in the ring road were likely caused by the poor state of pavement and higher share of heavy duty vehicles. Road wear, brake wear and a carbonaceous source, were almost equally responsible for 96% of RD10. At the traffic monitoring site located at the ring road (220,000 vehicle/day), the contributions of road dust emissions were estimated by receptor modeling to be 13% of PM10 on an annual mean (6.3 μg m −3 ), while the sum of vehicle exhaust and wear accounted for 47% resulting in a total traffic contribution of 60% of PM10. Road salting resulted to be a minor contributor (1% of annual mean) also in winter time (2%). [ABSTRACT FROM AUTHOR]

Brown carbon (i.e., light-absorbing organic carbon, or BrC) exerts important effects on the environment and on climate in particular. Based on spectrophotometric absorption measurements on extracts of bulk aerosol samples, this study investigated the characteristics of BrC during winter in Beijing, China. Organic compounds extractable by methanol contributed approximately 85% to the organic carbon (OC) mass. Light absorption by the methanol extracts exhibited a strong wavelength dependence, with an average absorption Ångström exponent of 7.10 (fitted between 310 and 450 nm). Normalizing the absorption coefficient ( b abs ) measured at 365 nm to the extractable OC mass yielded an average mass absorption efficiency (MAE) of 1.45 m 2 /g for the methanol extracts. This study suggests that light absorption by BrC could be comparable with black carbon in the spectral range of near-ultraviolet light. Our results also indicate that BrC absorption and thus BrC radiative forcing could be largely underestimated when using water-soluble organic carbon (WSOC) as a surrogate for BrC. Compared to previous work relying only on WSOC, this study provides a more comprehensive understanding of BrC aerosol based on methanol extraction. [ABSTRACT FROM AUTHOR]

Air exchange rates (AERs) have a direct impact on traffic-related air pollutant (TRAP) levels inside vehicles. Taxi drivers are occupationally exposed to TRAP on a daily basis, yet there is limited measurement of AERs in taxi cabs. To fill this gap, AERs were quantified in 22 representative Los Angeles taxi cabs including 10 Prius, 5 Crown Victoria, 3 Camry, 3 Caravan, and 1 Uplander under realistic driving (RD) conditions. To further study the impacts of window position and ventilation settings on taxi AERs, additional tests were conducted on 14 taxis with windows closed (WC) and on the other 8 taxis with not only windows closed but also medium fan speed (WC-MFS) under outdoor air mode. Under RD conditions, the AERs in all 22 cabs had a mean of 63 h −1 with a median of 38 h −1 . Similar AERs were observed under WC condition when compared to those measured under RD condition. Under WC-MFS condition, AERs were significantly increased in all taxi cabs, when compared with those measured under RD condition. A General Estimating Equation (GEE) model was developed and the modeling results showed that vehicle model was a significant factor in determining the AERs in taxi cabs under RD condition. Driving speed and car age were positively associated with AERs but not statistically significant. Overall, AERs measured in taxi cabs were much higher than typical AERs people usually encounter in indoor environments such as homes, offices, and even regular passenger vehicles. [ABSTRACT FROM AUTHOR]

Road dust is a non-exhaust source of atmospheric particulate by re-suspension. It is composed of particles originating from natural sources as well as other non-exhaust source such as tire, brake and asphalt wear. The discrimination between atmospheric particles directly emitted from abrasion process and those related to re-suspension is therefore an open issue, as far as the percentage contribution of non-exhaust emissions is becoming more considerable due also to the recent policy actions and the technological upgrades in the automotive field, focused on the reduction of exhaust emissions. In this paper, road dust collected along the bridge that connects Venice (Italy) to the mainland is characterized with a multi-technique approach in order to determine its composition depending on environmental as well as traffic-related conditions. Six pollutant sources of road dust particles were identified by cluster analysis: brake, railway, tire, asphalt, soil + marine, and mixed combustions. Considering the lack of information on this matrix in this area, this study is intended to provide useful information for future identification of road dust re-suspension source in atmospheric particulate. [ABSTRACT FROM AUTHOR]

For the source apportionment of carbonaceous aerosols, measurement of 14 C is an effective technique. In particular, diurnal variations of fossil and nonfossil carbonaceous aerosols provide information about the sources and production pathways of elemental carbon (EC) and organic carbon (OC). In this study, concentrations of fine-mode aerosols, including EC, OC, and 14 C, were observed with a time resolution of 6 h near the urban center of Beijing in June 2010. The observations indicate that the contribution of fossil secondary organic aerosol (SOA) increased during daytime. This finding is consistent with previous studies in other urban sites, suggesting that SOA production from anthropogenic sources is important in urban areas. We evaluated the performance of two chemical transport models (CTMs) with different SOA models on simulations of EC and OC. Both models well reproduced the concentration and diurnal variation of EC. OC concentrations were underestimated by more than half by the CTM with a SOA yield model, and were better reproduced by the CTM with a volatility basis set (VBS) model. However, even the VBS model underestimated both fossil and nonfossil total carbon (EC + OC), and possible reasons for this underestimation are discussed. [ABSTRACT FROM AUTHOR]

This paper documents the performance of the fully coupled WRF-Chem model at 21.6 km and 7.2 km resolution over Saudi Arabia in simulating a severe dust storm event that occurred in March 2009. The comparisons between the model simulations and the observed AOD at the Solar Village AERONET site and the MODIS measurements show that WRF-Chem satisfactorily resolves the arrival, evolution and spatial distributions of the dust storm over Saudi Arabia especially for the fine domain at 7.2 km resolution. The model simulated surface meteorological variables at Riyadh Airport, Hafr Al-Batin Airport, Dammam Airport and Gassim Airport follow the observations in terms of magnitude and temporal evolution although model biases such as deficiencies in simulating the amplitude of diurnal cycles are noted. Higher resolution and shorter initialization time improve the model performance in aerosol optical depth but for surface variables shorter initialization time improves correlation while higher horizontal resolution improves mean biases to some extent. The simulated dust plume is mainly confined between the surface and the 5-km height, with the peak concentrations located in the lowest 500 m. The vertical extent of the dust plume shows gradual decreases during the simulation period when averaged over the entire fine domain and an area centered around Solar Village, and also varies in accordance with the development and decay of the boundary layer. [ABSTRACT FROM AUTHOR]

Under the National Ambient Air Quality Standard released in 2012 (NAAQS-2012), Beijing began to publicize hourly Air Quality Index as well as real time concentrations of 6 pollutants in its web platform to provide detailed information for air quality assessment from 2013. In this study, hourly air quality monitoring data from May 2014 to April 2015 were collected for all 35 monitoring stations in Beijing to analyze the temporal and spatial variations of air pollutants and air quality. It is found that in spatial pattern, the air qualities in southern and northern Beijing are totally different. The association between heavy pollution concentrations and wind situations suggested that neighboring area's air quality has an important role in the air quality of Beijing combining with air quality attainment rates in all 35 monitoring stations and northern China. For temporal variations, late night and early morning are the most polluted time while afternoon is the least polluted time for all pollutants except O 3 with most polluted time in afternoon. Summer time in Beijing has the best air quality while winter time has the worst air quality coinciding with the heating season in the winter. [ABSTRACT FROM AUTHOR]

The spatial distribution of PM sources affecting Athens (Greece) was determined by introducing in the Concentration Weighted Trajectory (CWT) algorithm PM 2.5 concentration and composition data from an urban background site. The produced 0.5° × 0.5° resolution maps clearly revealed the impact of anthropogenic and natural sources and the relative contribution of regional and transboundary emissions in PM 2.5 mass. For sulfates, ammonium and organic carbon, a significant regional contribution derives from Northern airflows through Greece and Balkan Peninsula (mainly Bulgaria). Air masses incoming from North-West Africa, during Saharan dust outbreaks, and the Mediterranean, are charged with aerosol constituents from different combustion sources such as nitrates. Sea spray originates from the Ionian Sea and also from southern directions through Saronikos Gulf. The intrusion of Saharan dust is responsible for the concentration maxima of the elements of crustal/main crustal origin, and was almost exclusively associated with S-SW airflows through Algeria, Tunisia and Libya. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) correlation spectroscopy, applied to one-dimensional solid-state cross polarization magic angle spinning (CP-MAS) 13 C nuclear magnetic resonance (NMR), Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR), and the combination of CP-MAS 13 C NMR and FTIR-ATR data, has been used to glean new structural information on the most hydrophobic water-soluble organic matter (WSOM) from fine urban air particles collected during different seasons. CP-MAS 13 C NMR analysis confirmed that unsubstituted saturated aliphatics, aromatics, oxygenated aliphatics, and carboxylic acids accounted for most (84–92%) of the characterized carbon functional groups. Applying 2D correlation spectroscopy to CP-MAS 13 C NMR and FTIR-ATR spectra indicates an increase in the contribution of hydroxyl and carboxylic groups to the aliphatic component with increasing air temperature, suggesting the photo-chemical origin of these WSOM structures. Urban samples from colder periods are clearly impacted by biomass combustion sources, although the presence of aged and processed organic aerosols cannot be ruled out. Using 2D FTIR- 13 C NMR hetero-spectral correlation spectroscopy, it has been demonstrated that the studied WSOM samples consists of at least two different classes of compounds: (i) an aliphatic component rich in both carboxylic and hydroxyl functional groups, and (ii) lignin-derived structures. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5 ) has attracted increasing attention due to its impacts on air quality and human health. As an important source of PM 2.5 , diesel vehicles are often the focus of research. In this study, we characterized the carbonaceous composition of PM 2.5 that is emitted from on-road China III diesel trucks (DTs). Organic carbon (OC), elemental carbon (EC), and PM 2.5 emission characteristics were determined for 17 China III DTs, including 6 light-duty diesel trucks (LDDTs), 5 medium-duty diesel trucks (MDDTs), and 6 heavy-duty diesel trucks (HDDTs), based on real-world measurements in Beijing, China, using a portable emissions measurement system (PEMS). The average distance-based PM 2.5 emission factors (EFs) (g km −1 ) generally increased and the average CO 2 -based PM 2.5 EFs (g (kg of CO 2 ) −1 ) generally decreased with increased vehicle size from LDDTs to MDDTs to HDDTs. The effects of driving conditions on the EFs for carbonaceous PM 2.5 were analyzed. The results show that distance-based and CO 2 -based EFs strongly depend on driving conditions. Generally, greater amounts of PM 2.5 and OC are emitted from non-highway driving cycles, and greater amounts of EC are emitted from highway driving cycles for vehicles of the same size. For LDDTs, MDDTs, and HDDTs, no significant differences were observed between vehicles with different EC/OC ratios; therefore, the EC/OC ratio is not useful for distinguishing between the emissions generated by differently sized vehicles. The EC/OC, OC/PM 2.5 , and EC/PM 2.5 mass ratios are strongly dependent on driving conditions for vehicles of the same size. The results of this study provide EFs for the carbonaceous composition of PM 2.5 that are more appropriate for China; these results will be helpful for improving policies that are designed to control the carbonaceous composition of PM 2.5 emitted from on-road DTs in China. [ABSTRACT FROM AUTHOR]

The chemical characterization of PM2.5 fraction was studied during a one-year sampling campaign conducted at an urban area (city center) of Thessaloniki, Greece. PM2.5 samples were analyzed for polycyclic aromatic hydrocarbons, minerals and trace elements, water soluble ions, organic and elemental carbon. The average PM2.5 concentration (37.7 μg/m 3 ) was significantly higher than the EU legislated annual limit of 25 μg/m 3 underlining the temporal problems of air quality in the city. PM mass and chemical composition data collected at the city center were compared to the corresponding data which were simultaneously collected at a site near the port. The atmosphere in the port area has been found to be more aggravated compared to the city center area. Statistical analysis and diagnostic ratios of the collected chemical data at both sites were used to identify the main sources contributing to the pollutant levels: traffic, biomass burning for domestic heating, shipping and port activities and dust resuspension. In general, chemical analysis highlighted that PM2.5 mass was mainly composed by secondary inorganic aerosols and particulate organic matter, reflecting the simultaneous contribution of both regional and local emission sources. [ABSTRACT FROM AUTHOR]

To better understand the chemical speciation of volatile organic compounds (VOCs) and their role in ground-level ozone formation in the Beijing-Tianjin-Hebei region, China, measurements of 56 non-methane hydrocarbons (NMHCs) and 12 carbonyls were conducted at three sites in summer. Alkanes were the largest group of NMHCs (>50%), followed by alkenes and aromatics. Acetone was the most abundant carbonyl species (>50%). The OH loss rates (L OH ) of VOCs were calculated to estimate their chemical reactivities. Alkenes played a predominant role in VOC reactivity, among which ethene and propene were the largest contributors. Isoprene contributed 11.61–38.00% of the total reactivity of measured VOCs. Alkenes and aromatics were the largest contributors (47.65–61.53% totally) to the total Ozone Formation Potential (OFP) of measured VOCs based on the observed mixing ratio. Isoprene was the most reactive species, but originated mainly from biogenic emissions. Ethene, m/p-xylene, toluene, propene, o-xylene, and 1-butene were considered to play significant roles in ground-level ozone formation in this region. The OFPs of total measured NMHCs increased by 10.20–22.05% when they were calculated based on the initial mixing ratio. Photochemical losses of hydrocarbons and the secondary formation of carbonyls in this region were also determined. Vehicle exhaust emissions contributed substantially to ambient VOCs. [ABSTRACT FROM AUTHOR]

Predicting pollutant dispersion in urban environments requires accurate treatment of obstacle geometry, inflow turbulence and temperature differences. This paper considers both the influence of thermal stratification and the presence of a single obstacle on pollutant dispersion in turbulent boundary layers (TBLs). Turbulent flow over a fence with line sources of pollutant in its vicinity is simulated by means of Large-Eddy Simulations. Separate ‘driver’ simulations are done to generate the inflow TBL for several levels of stratification. Using these inflow TBLs the flow development and pollutant dispersion behind the fence, up to 100 fence heights, h , is investigated. It is shown that the decay of velocity and temperature deficit is independent of stability, while the decay of Reynolds stress and concentration excess decreases with increasing stability. For neutral cases the influence of the obstacle is gone after approximately 75 h , while for stable cases near the ground the flow is still accelerated compared to the undisturbed case. The fence does cause a local reduction of stratification and thereby increased pollutant dispersion. However, neglecting the effect of buoyancy results in an underestimation of pollutant concentration by a factor 2.5 at 75 h downstream of the emission source for the most stable case. [ABSTRACT FROM AUTHOR]

Ships and harbour emissions are currently increasing, due to the increase of tourism and trade, with potential impact on global air pollution and climate. At local scale, in-port ship emissions influence air quality in coastal areas impacting on health of coastal communities. International legislations to reduce ship emissions, both at Worldwide and European levels, are mainly based on the use of low-sulphur content fuel. In this work an analysis of the inter-annual trends of primary contribution, ε , of tourist shipping to the atmospheric PM 2.5 concentrations in the urban area of Venice has been performed. Measurements have been taken in the summer periods of 2007, 2009 and 2012. Results show a decrease of ε from 7% (±1%) in 2007 to 5% (±1%) in 2009 and to 3.5% (±1%) in 2012. The meteorological and micrometeorological conditions of the campaigns were similar. Tourist ship traffic during measurement campaigns increased, in terms of gross tonnage, of about 25.4% from 2007 to 2009 and of 17.6% from 2009 to 2012. The decrease of ε was associated to the effect of a voluntary agreement (Venice Blue Flag) for the use of low-sulphur content fuel enforced in the area between 2007 and 2009 and to the implementation of the 2005/33/CE Directive in 2010. Results show that the use of low-sulphur fuel could effectively reduce the impact of shipping to atmospheric primary particles at local scale. Further, voluntary agreement could also be effective in reducing the impact of shipping on local air quality in coastal areas. [ABSTRACT FROM AUTHOR]

Delhi has been listed as the worst performer across the world with respect to the presence of alarmingly high level of haze episodes, exposing the residents here to a host of diseases including respiratory disease, chronic obstructive pulmonary disorder and lung cancer. This study aimed to analyze the haze episodes in a year and to develop the forecasting methodologies for it. The air pollutants, e.g., CO, O 3 , NO 2 , SO 2 , PM 2.5 as well as meteorological parameters (pressure, temperature, wind speed, wind direction index, relative humidity, visibility, dew point temperature, etc.) have been used in the present study to analyze the haze episodes in Delhi urban area. The nature of these episodes, their possible causes, and their major features are discussed in terms of fine particulate matter (PM 2.5 ) and relative humidity. The correlation matrix shows that temperature, pressure, wind speed, O 3 , and dew point temperature are the dominating variables for PM 2.5 concentrations in Delhi. The hour-by-hour analysis of past data pattern at different monitoring stations suggest that the haze hours were occurred approximately 48% of the total observed hours in the year, 2012 over Delhi urban area. The haze hour forecasting models in terms of PM 2.5 concentrations (more than 50 μg/m 3 ) and relative humidity (less than 90%) have been developed through artificial intelligence based Neuro-Fuzzy (NF) techniques and compared with the other modeling techniques e.g., multiple linear regression (MLR), and artificial neural network (ANN). The haze hour's data for nine months, i.e. from January to September have been chosen for training and remaining three months, i.e., October to December in the year 2012 are chosen for validation of the developed models. The forecasted results are compared with the observed values with different statistical measures, e.g., correlation coefficients ( R ), normalized mean square error (NMSE), fractional bias (FB) and index of agreement (IOA). The performed analysis has indicated that R has values 0.25 for MLR, 0.53 for ANN, and NF: 0.72, between the observed and predicted PM 2.5 concentrations during haze hours invalidation period. The results show that the artificial intelligence implementations have a more reasonable agreement with the observed values. Finally, it can be concluded that the most convincing advantage of artificial intelligence based NF model is capable for better forecasting of haze episodes in Delhi urban area than ANN and MLR models. [ABSTRACT FROM AUTHOR]

In this study, the pollution status of particulate matter (PM) in ambient air was investigated based on the concentration data of three important PM fractions (PM 2.5 , PM 10 , and TSP) measured from a central area in Seoul, Korea during the period from 2004 to 2013. The mean concentrations of each fraction measured for the entire study period were found to be 26.6 ± 2.59, 54.0 ± 15.0, and 75.3 ± 16.6 μg m −3 , respectively. The seasonal mean of PM 2.5 varied in the range of 22.9 ± 7.10 (fall) to 30.2 ± 7.58 μg m −3 (winter). In contrast, PM 10 and TSP showed a summer minimum (40.1 ± 12.6 and 55.6 ± 17.8 μg m −3 , respectively) and a spring maximum (67.1 ± 16.7 and 93.7 ± 21.1 μg m −3 , respectively). The contribution of regional or long-range transport to the observed PM levels in the study area, if estimated by comparison to the data of the regional background area, was found to explain up to 72% of its input. The long-term trend of PM indicated a gradual decreasing pattern over a 10 year period, although that of PM 2.5 was rather complicated to interpret in the recent years. The overall results of our study nonetheless confirm the potent role of legislation efforts put consistently to improve the air quality through the years. [ABSTRACT FROM AUTHOR]

Polycyclic Aromatic Hydrocarbons (PAHs) are considered among the most dangerous air pollutants due to their carcinogenic and mutagenic characteristics. Populations living in urban area are exposed to these pollutants because of their proximity to the emission sources. However, the spatial and temporal characteristics of PAHs concentrations in such areas are not well known. An integrated modeling approach is here presented to estimate exposure to PAHs content in PM 2.5 of children and elderly people living in the city of Rome, Italy. It is based on a microenvironment approach in which exposure is estimated by accounting for PAHs concentrations experienced by the target population in the most visited living environments. The model uses data provided by the EU LIFE + EXPAH project: indoor/outdoor PAHs concentrations collected in homes, schools, cars, buses and offices to derive PAHs infiltration factors for the specific environments; time activity to identify daytime profiles of the target population and information on the prevailing living environments; ambient PAHs concentration fields. The latter have been obtained by integrating Chemical Transport Model (CTM) results with measurements collected by the EXPAH project. Uncertainties in the estimation of PAHs exposure has been evaluated by applying a Monte Carlo statistical approach using probability density function based on observed exposure parameters. Results were calculated for one year (June 2011–May 2012). The downtown area was found to be the most contaminated one with concentrations up to 2 ± 1 and 0.6 ± 0.2 ng/m 3 , on an annual basis, respectively for ∑ 4 PAHs (e.g. B[a]P, B[b]F, B[k]F and indeno(1,2,3-cd)pyrene) and B[a]P. Results do not exhibit significant differences on ∑ 4 PAHs exposure between children and elderly people, mainly due to the prevalence of indoor microenvironments in the time activity data, and to the little difference in the indoor/outdoor infiltration. Seasonality was identified as an important factor contributing to the overall exposure. The higher PAHs emissions during the heating period determine a greater exposure during winter. Homes have been identified as the microenvironments that most contribute to PAHs exposure followed by schools. [ABSTRACT FROM AUTHOR]

The detection of nicotine, an organic tracer for Environmental Tobacco Smoke (ETS), in the collected PM 10 samples from Delhi region's ambient environment, in a appropriately designed investigation was initiated over four years (2006–2009) to: (1) Comprehend seasonal and inter-annual variations in the nicotine present in PM 10 ; (2) Extract regression based linear trend profile manifested by nicotine in PM 10 ; (3) Determine the non-linear trend timeline from the nicotine data, and compare it with the obtained linear trend; (4) Suggest the possible use of the designed experiment and analysis to have a qualitative appraisal of Tobacco Smoking activity in the sampling region. The PM 10 samples were collected in a monthly time-series sequence at a known receptor site. Quantitative estimates of nicotine (ng m −3 ) were made by using a Thermal Desorption Gas Chromatography Mass Spectrometry (TD-GC/MS). The annual average concentrations of nicotine (ng m −3 ) were 516 ± 302 (2008) > 494 ± 301 (2009) > 438 ± 250 (2007) > 325 ± 149 (2006). The estimated linear trend of 5.4 ng m −3 month −1 corresponded to 16.3% per annum increase in the PM 10 associated nicotine. The industrial production of India's tobacco index normalized to Delhi region's consumption, pegged an increase at 10.5% per annum over this period. [ABSTRACT FROM AUTHOR]

In this paper, we conducted a comparative study of new particle formation (NPF) events occurring between Qingdao and Toronto during spring. The extent of air pollution in Qingdao was much severer than that in Toronto, but the occurrence frequency of NPF events in Qingdao (41%) was almost same as that (42%) in Toronto. The geometric median diameter of new particles (D pg,1 ) increased up to >40 nm in 15 days out of the total 16 NPF days in Qingdao, the D pg,1 at least in eight days increased up to >60 nm and even reached >80 nm in two days. Two-stage growth was generally observed in these eight NPF events. The first-stage growth occurred in daytime and it was likely associated with formation of secondary organic aerosol (SOA) on basis of the modeling results. The second-stage growth was generally observed at nighttime when the modeling results showed increases of NH 4 + and NO 3 − in concentration together with SOA, implying that NH 4 NO 3 possibly played a role in the growth. In Toronto, the maximum D pg,1 of the observed new particles in all 13 NPF events was less than 50 nm. A slight second-stage growth of new particles was observed only in four days when either the increase of NH 4 + and NO 3 − in concentration or the increase of relative humidity occurred. The NPF events in Toronto less likely had a significant contribution to cloud condensation nuclei due to the small size of the observed new particles. [ABSTRACT FROM AUTHOR]

Abstract: Residual aerosols, the particles left behind after droplet evaporation, are important tracers for aerosols processed by cloud and/or fog. Based on ground-based CIMEL sun–sky radiometer measurements during an extreme winter pollution event in Beijing, we present observations of the decrease of residual aerosol with dissipation of cloud and an unusual case of residual aerosol increase after partial dissipation of fog. This unusual increase might be an important mechanism for the haze growth in polluted regions. The aerosol single scattering albedo is found to increase with the increase of residual aerosol. We also find that residual aerosol dominated cases with significant water content gain can occur in a short time (e.g. one hour) with the increase of aerosol volume size and decrease of particle number. A lognormal residual aerosol size distribution model is proposed based on sun–sky radiometer measurements with center peak radius at 0.44 micron and geometric standard deviation of about 1.49. [Copyright &y& Elsevier]

Abstract: Particulate matter (PM10) associated with polycyclic aromatic hydrocarbons (PAHs) in ambient air were determined at two sites within the Klang Valley, Kuala Lumpur (urban, KL) and Petaling Jaya (industrial, PJ), and one site outside the Klang Valley, Bangi (semi-urban, BG). This study aimed to determine the concentration and distribution of PAHs in PM10 and the source of origin through principal component analysis (PCA) and diagnostic ratio analysis. This study also assessed the health risk from exposure to airborne BaPeq. PM10 samples were collected on glass fiber filter paper using a High Volume Sampler (HVS) for 24 h between September 2010 and April 2011. The filter papers with PM10 were extracted using dichloromethane-methanol (3:1), and analysis of 16 USEPA priority PAHs was determined using gas chromatography with mass spectra (GC–MS). Health risk assessment was estimated using toxic equivalency factors (TEFs) and incremental lifetime cancer risk (ILCR) which quantitatively estimate the exposure risk for age specific group. The results showed that the total PAHs concentrations throughout seasonal monsoons for KL, PJ and BG ranged from 1.33 ng m−3 to 2.97 ng m−3, 2.24 ng m−3 to 4.84 ng m−3 and 1.64 ng m−3 to 3.45 ng m−3 respectively. More than 80% of total PAHs consisted of 5-ring and 6-ring PAHs such as benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IcP), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF) and benzo[g,h,i]perylene (BgP). The presence of benzo[g,h,i]perylene (BgP) with high concentration at all locations suggested a source indicator for traffic emission. PCA and diagnostic ratio analysis also suggested substantial contributions from traffic emission with minimal influence from coal combustion and natural gas emissions. The use of total BaPeq concentration provide a better estimation of carcinogenicity activities, where they contributed to more than 50% of the potential health risk. Health risk assessment showed that the estimated incremental lifetime cancer risk (ILCR) from exposure to airborne BaPeq is negligible at all sampling sites for all age specific group. [Copyright &y& Elsevier]

Abstract: Anthropogenic heat released into the atmosphere in urban areas affects the characteristics/structures of boundary layer and local circulation and thus can affect local air quality. In this study, the effects of anthropogenic heat on ozone (O3) air quality in the Seoul metropolitan area, Republic of Korea, are examined using the Community Multiscale Air Quality (CMAQ) model coupled with the Weather Research and Forecasting (WRF) model. The release of anthropogenic heat is found to increase O3 concentration by 3.8 ppb in the urban area, and this effect is larger in the nighttime (5.3 ppb) than in the daytime (2.4 ppb). As stronger anthropogenic heat is released, the urban boundary layer becomes deeper and NO x concentration becomes lower due to the dilution. The decrease in NO x concentration causes the chemical loss of O3 by the reaction with NO to be reduced. In addition to the enhanced net chemical production of O3 in the deepened urban boundary layer, the strengthened urban-breeze circulation by anthropogenic heat contributes to an increase in O3 concentration in the urban area. The O3-rich air in the surroundings of Seoul, where biogenic volatile organic compound (BVOC) emissions are high and NO x emissions are low, is brought into the urban area by the urban breeze. Moreover, in the daytime, the advection of oxidant products of BVOCs by the urban breeze contributes to an enhanced chemical production of O3 in the urban area. Anthropogenic heat also modifies the sea/land-breeze circulations, which, in turn, is found to influence O3 concentration in the urban area. [Copyright &y& Elsevier]

Abstract: The study investigates thermal stratification effects of approach flows on dispersion in urban environments. This is in some ways analogous to a well-developed non-neutral flow (e.g. through a large urban area) approaching a neighbourhood-scale urban region, where the effect of the local heat transfer was assumed less important. A generic urban-type geometry, i.e. a group of staggered cubes, was taken as the first test case. The DAPPLE site, which was about a one-km2 region near the intersection of Marylebone Road and Gloucester Place in central London, was taken as the second test case. Only weakly unstable conditions (i.e. bulk Richardson number ) of approach flows were considered, with adiabatic boundary conditions at the ground and building surfaces. A number of numerical experiments were performed. The modelled mean concentration for R b = −0.1 gave the best agreement with the field data at all DAPPLE stations. This suggests that stratification effects on dispersion in weakly unstable conditions (e.g. in London) are not negligible. [Copyright &y& Elsevier]

Abstract: The contribution of regional, urban and traffic sources to PM2.5 and PM10 in an urban area was investigated in this study. The chemical composition of PM2.5 and PM10 was measured over a year at a street location and up- and down-wind of the city of Rotterdam, the Netherlands. The 14C content in EC and OC concentrations was also determined, to distinguish the contribution from “modern” carbon (e.g., biogenic emissions, biomass burning and wildfires) and fossil fuel combustion. It was concluded that the urban background of PM2.5 and PM10 is dominated by the regional background, and that primary and secondary PM emission by urban sources contribute less than 15%. The 14C analysis revealed that 70% of OC originates from modern carbon and 30% from fossil fuel combustion. The corresponding percentages for EC are, respectively 17% and 83%. It is concluded that in particular the urban population living in street canyons with intense road traffic has potential health risks. This is due to exposure to elevated concentrations of a factor two for EC from exhaust emissions in PM2.5 and a factor 2–3 for heavy metals from brake and tyre wear, and re-suspended road dust in PM10. It follows that local air quality management may focus on local measures to street canyons with intense road traffic. [Copyright &y& Elsevier]

Abstract: Currently, the depiction of urban air quality at boundary layer scale uses modelled climatic and land cover data. However, such models are difficult to verify, and only low to moderate accuracy may be achieved due to the complexity of the input data required and the reliance on assumptions about dispersion patterns. The provision of comprehensive air quality data to urban residents in city districts, at a level of detail commensurate with other Location-Based Services (LBS) which are time- and place-sensitive, has therefore not been possible. A method for urban air quality monitoring over cities at boundary layer scale, other than by the use of air quality models is presented here. The system presented uses empirical Aerosol Optical Thickness (AOT) data in near-real time, combining AOT data from AERONET with aerosol vertical profiles computed from twice-daily MODIS satellite images at 500m resolution, to give three dimensional (3D) air quality data over the urban landscape. There has been no previous attempt to project the horizontal spatial distribution of aerosols from satellite image pixels into a vertical dimension to give a spatially comprehensive three dimensional record of air quality. The paper describes the sources and accuracy of the AOT data input to the system as well as its storage and retrieval on a Geographic Information System (GIS) platform, to provide air quality and visibility information according to user query at any 3D geographical location, including individual buildings or building floor. [Copyright &y& Elsevier]

Traditional regulatory methods for evaluating air toxics have several limitations. Two common methods rely either on self-reported industrial emissions from the Toxics Release Inventory or a single summary statistic such as the average or arithmetic mean. A novel statistical approach for detecting overall long term improvement in ambient air quality is demonstrated using measurements of the air toxic benzene evaluated over five years in Houston, Texas. Through trends of seven key statistical measures, long term improvements were detected at more monitors than would have been found using traditional methods while lack of improvement is highlighted at other monitors. This new approach includes analysis of high and low end concentrations, as well as central tendency, evaluated at specific air toxic human health risk thresholds. [Copyright &y& Elsevier]

We use ensemble-mean Lagrangian sampling of a 3-D Eulerian air quality model, CMAQ, together with ground-based ambient monitors data from several air monitoring networks and satellite (MODIS) observations to provide source apportionment and regional transport vs. local contributions to sulfate aerosol and PM2.5 concentrations at Baltimore, MD, for summer 2004. The Lagrangian method provides estimates of the chemical and physical evolution of air arriving in the daytime boundary layer at Baltimore. Study results indicate a dominant role for regional transport contributions on those days when sulfate air pollution is highest in Baltimore, with a principal transport pathway from the Ohio River Valley (ORV) through southern Pennsylvania and Maryland, consistent with earlier studies. Thus, reductions in sulfur emissions from the ORV under the EPA''s Clean Air Interstate Rule may be expected to improve particulate air quality in Baltimore during summer. The Lagrangian sampling of CMAQ offers an inexpensive and complimentary approach to traditional methods of source apportionment based on multivariate observational data analysis, and air quality model emissions separation. This study serves as a prototype for the method applied to Baltimore. EPA is establishing a system to allow air quality planners to readily produce and access equivalent results for locations of their choice. [Copyright &y& Elsevier]