Mass Concentrations Of PM2 Research Articles

Real‐Time Characterization of Aerosol Compositions, Sources, and Aging Processes in Guangzhou During PRIDE‐GBA 2018 Campaign

AbstractTo investigate the chemical compositions, sources, and aging processes of submicron particles (PM1), a comprehensive field campaign was conducted in Guangzhou urban area of China during the autumn (October–November) of 2018. The average mass concentration of PM1 was 35.6 ± 20.8 µg m−3, which was mainly contributed by organic aerosols (OA, 42%), then followed by sulfate (25%) and inorganic nitrate (11%). The inorganic nitrate was found to be the main driving component (up to ∼50%) to account for the fast increase of PM1 during the polluted periods of Guangzhou autumn. The promotion effects of sulfate, aerosol liquid water content, and particles acidity on nitrate formation were systematically discussed. Source apportionment results showed 72% of OA in Guangzhou autumn was contributed by secondary OA (SOA), and 28% of primary OA (POA), including vehicle emission related hydrocarbon‐like OA (HOA, 16%), nitrogen‐containing OA (NOA, 3%) and cooking OA (COA, 8%). To explore the aging processes of OA, the dynamic variations of OA and its oxidation level as a function of ambient photochemical age are shown. Using an in situ field‐deployed oxidation flow reactor, the heterogeneous reaction rate coefficients of ambient POA with OH radicals () were estimated to be 4.0–5.4 × 10−13 cm3 molecules−1 s−1, which is equivalent to a lifetime of POA >2 weeks. The long heterogeneous lifetime of POA supports gas phase oxidation was the major pathway for ambient OA aging. The OH uptake coefficient () was estimated to be 0.76–0.84, underlining that OH radicals can be taken up efficiently on ambient aerosols.

Experimental study of smog microphysical and optical vertical structure in the Silesian Beskids, Poland

This study presents the vertical profiles of aerosol optical and microphysical properties obtained from cable car and ground-based measurements in the Silesian Beskids, Poland. The data were collected during a measurement campaign between 25 February and March 11, 2018. An AE-51 micro-aethalometer and PMS7003 and OPC-N2 optical particle counters were mounted on the cable car and used to measure the profiles of equivalent of black carbon (eBC) concentration and aerosol size distribution. In situ measurements of the optical properties of the aerosols were obtained using an AE-31 aethalometer and photoacoustic devices. A prototype lidar was used to determine the planetary boundary layer (PBL) height and the aerosol layers. In the middle phase of the study (1–6 March 2018), significant night-time temperature inversions were observed. During the inversion period, the parameters describing the amount of aerosols in the air increased significantly. The concentration of eBC exceeded the level of 15 μg/m3 several times, with an average level of 5.39 ± 4.42 μg/m3. Conversely, the results obtained in the first and third phases of the experiment were at the level of the aerosol background, being 1.45 ± 0.88 μg/m3 and 0.90 ± 0.95 μg/m3, respectively. Significant differences were also observed in the vertical profiles of PM10 mass and eBC concentration. In the middle phase of the study, the profiles showed a significant reduction in the concentration of pollutants with height, while in the first and third phases, there were slight variations with height.

Improvements of ADAM3 by Incorporating New Dust Emission Reduction Formulations Based on Real-Time MODIS NDVI

Dust events in Northeast Asia have several adverse effects on human health, agricultural land, infrastructure, and transport. Wind speed is the most important factor in determining the total dust emission at the land surface; however, various land-surface conditions must be considered as well. Recently, the Korea Meteorological Administration updated the dust emission reduction factor (RF) in the Asian Dust Aerosol Model 3 (ADAM3) using data from the normalized difference vegetation index (NDVI) of the Moderate Resolution Imaging Spectroradiometer (MODIS). We evaluated the improvements of ADAM3 according to soil types. We incorporated new RF formulations in the evaluation based on real-time MODIS NDVI data obtained over the Asian dust source regions in northern China during spring 2017. This incorporation improved the simulation performance of ADAM3 for the PM10 mass concentration in Inner Mongolia and Manchuria for all soil types, except Gobi. The ADAM3 skill scores for sand, loess, and mixed types in a 24 h forecast increased by 6.6%, 20.4%, and 13.3%, respectively, compared with those in forecasts employing the monthly RF based on the NDVI data. As surface conditions in the dust source regions continually change, incorporating real-time vegetation data is critical to improving performance of dust forecast models such as ADAM3.

Characterization of haze pollution in Zibo, China: Temporal series, secondary species formation, and PMx distribution

An online field observation was conducted in Zibo, China from September 1, 2018 to February 28, 2019, covering autumn and winter. Within the investigation period, the mean mass concentrations of PM1, PM2.5, and PM10 were 49.3, 86.1, and 136.5 μg m−3, respectively. OA (organic aerosol) was the most dominant species in PM2.5 (39.7 %), followed by NO3− (26.3 %) and SO42− (17.0 %), indicating the importance of secondary species on PM2.5. Increase of particles were always accompanied increasing relative humidity (RH), slow wind, and increasing precursors, contributing the secondary transition. SO42− was more susceptible to RH, indicating the dominant role of heterogeneous processes in its secondary formation. As RH increased, its strengthening effect on SO42− increased as well. Photochemistry was the main contributor to the secondary formation of NO3−. The morning and evening rush hours determined the peak of absolute NO3− throughout the day. By classifying particles into three bins, we found that smaller particles were the biggest contributors (larger PM1/PM2.5) of slight pollution (35 < PM2.5<115 μg m−3). When severe haze occurred, PM2.5 contributed more than particles of other sizes (PM1 or PM10). Secondary species contributed more to particles within 2.5 μm but less to larger particles. PM1/PM2.5 was high from 9:00 to 15:00, indicating the strong effect of photochemistry on smaller particles. In comparison, larger particles favored more humid conditions. NO3− preferentially existed in larger particles because the hygroscopicity of preexisting species (SO42− and NO3−) promoted partitioning. SO42− appeared a stable diurnal variation, replying its stable contribution to particles of different sizes.

Changes in the concentration and composition of urban aerosols during the COVID-19 lockdown

This work investigates the impact of COVID-19 restrictive measures on the mass concentrations of PM1 and PM10, and their chemical components (water-soluble ions, organic and elemental carbon, and major and trace metals) at an urban site in the western Mediterranean. The evolution of gaseous pollutants (NOx, O3 and some volatile organic compounds) was also analyzed. The concentrations measured during the lockdown in 2020 were compared to those obtained during the same period over the preceding five years. The average decrease in the levels of NOx and traffic-related volatile organic compounds was higher than 50 %, while O3 concentrations did not exhibit significant variations during the study period. Our results show that temporal variations in PM1 and PM10 concentrations were strongly affected by the frequency of Saharan dust events. When these episodes were excluded from the analysis period, a 35 % decrease in PM1 and PM10 levels was observed. Traffic restrictions during the lockdown led to important reductions in the concentrations of elemental carbon and metals derived from road dust (e.g. Ca and Fe) and break wear (e.g. Cu). Regarding secondary inorganic aerosols, nitrate showed the largest reductions as a consequence of the drop in local emissions of NOx.

Comparison of source apportionment approaches and analysis of non-linearity in a real case model application

Abstract. The response of particulate matter (PM) concentrations to emission reductions was analysed by assessing the results obtained with two different source apportionment approaches. The brute force (BF) method source impacts, computed at various emission reduction levels using two chemical transport models (CAMx and FARM), were compared with the contributions obtained with the tagged species (TS) approach (CAMx with the PSAT module). The study focused on the main sources of secondary inorganic aerosol precursors in the Po Valley (northern Italy): agriculture, road transport, industry and residential combustion. The interaction terms between different sources obtained from a factor decomposition analysis were used as indicators of non-linear PM10 concentration responses to individual source emission reductions. Moreover, such interaction terms were analysed in light of the free ammonia / total nitrate gas ratio to determine the relationships between the chemical regime and the non-linearity at selected sites. The impacts of the different sources were not proportional to the emission reductions, and such non-linearity was most relevant for 100 % emission reduction levels compared with smaller reduction levels (50 % and 20 %). Such differences between emission reduction levels were connected to the extent to which they modify the chemical regime in the base case. Non-linearity was mainly associated with agriculture and the interaction of this source with road transport and, to a lesser extent, with industry. Actually, the mass concentrations of PM10 allocated to agriculture by the TS and BF approaches were significantly different when a 100 % emission reduction was applied. However, in many situations the non-linearity in PM10 annual average source allocation was negligible, and the TS and BF approaches provided comparable results. PM mass concentrations attributed to the same sources by TS and BF were highly comparable in terms of spatial patterns and quantification of the source allocation for industry, transport and residential combustion. The conclusions obtained in this study for PM10 are also applicable to PM2.5.

Seasonal Variability of the Airborne Eukaryotic Community Structure at a Coastal Site of the Central Mediterranean.

The atmosphere represents an underexplored temporary habitat for airborne microbial communities such as eukaryotes, whose taxonomic structure changes across different locations and/or regions as a function of both survival conditions and sources. A preliminary dataset on the seasonal dependence of the airborne eukaryotic community biodiversity, detected in PM10 samples collected from July 2018 to June 2019 at a coastal site representative of the Central Mediterranean, is provided in this study. Viridiplantae and Fungi were the most abundant eukaryotic kingdoms. Streptophyta was the prevailing Viridiplantae phylum, whilst Ascomycota and Basidiomycota were the prevailing Fungi phyla. Brassica and Panicum were the most abundant Streptophyta genera in winter and summer, respectively, whereas Olea was the most abundant genus in spring and autumn. With regards to Fungi, Botrytis and Colletotrichum were the most abundant Ascomycota genera, reaching the highest abundance in spring and summer, respectively, while Cryptococcus and Ustilago were the most abundant Basidiomycota genera, and reached the highest abundance in winter and spring, respectively. The genus community structure in the PM10 samples varied day-by-day, and mainly along with the seasons. The impact of long-range transported air masses on the same structure was also proven. Nevertheless, rather few genera were significantly correlated with meteorological parameters and PM10 mass concentrations. The PCoA plots and non-parametric Spearman’s rank-order correlation coefficients showed that the strongest correlations generally occurred between parameters reaching high abundances/values in the same season or PM10 sample. Moreover, the screening of potential pathogenic fungi allowed us to detect seven potential pathogenic genera in our PM10 samples. We also found that, with the exception of Panicum and Physcomitrella, all of the most abundant and pervasive identified Streptophyta genera could serve as potential sources of aeroallergens in the studied area.

Associations of ultrafine and fine particles with childhood emergency room visits for respiratory diseases in a megacity

BackgroundAmbient fine particulate matter with aerodynamic diameter less than 2.5 µm (PM2.5) has been associated with deteriorated respiratory health, but evidence on particles in smaller sizes and childhood respiratory health...

Preliminary study: health risk analysis of PM2.5 and PM10 mass concentrations in Bandung Metropolitan

Particulate matters with sizes below 10 (PM10) and 2.5 (PM2.5) micrometers under polluted air have been causing not only climate change directly/indirectly but also public health problems. These were depended on the level concentrations of PM, chemical species, duration of exposure, as well as meteorological conditions, and how close we are to the emission sources. The aim of the preliminary study is to observe how air pollution concentrations can affect human health. We selected Bandung Metropolitan as a pilot project and located several instruments at Telkom University in the period of 2018-2019. PM2.5 and PM10 data were produced and calculated from microsensors. Health data and related patients from the hospital within 6 km were added to AirQ+ for short and long-term exposure analysis. Results show that temporal data of PM2.5 and PM10 were identified as <20 µg/m3 (in a wet season) to >100 µg/m3 (dry season). In long-term exposure to polluted air, PM2.5 contributed to mortality caused by Chronic Obstructive Pulmonary Disease (COPD) and ischemic heart disease. Meanwhile, post-neo-natal were observed under PM10 mass concentrations. In a short-term period of measurement, March to April and July to August, the respiratory disease has dominant across seasons. Therefore, the coupling of changes in climate and air pollution level will be negatively contributed to more effect on human health.

Fractal Analysis and Interpretation of Temporal Patterns of TSP and PM10 Mass Concentration over Tarkwa, Ghana

Fractal Analysis and Interpretation of Temporal Patterns of TSP and PM10 Mass Concentration over Tarkwa, Ghana

Physical and chemical properties of urban aerosols in São Paulo, Brazil: links between composition and size distribution of submicron particles

Abstract. In this work, the relationships between size and composition of submicron particles (PM1) were analyzed at an urban site in the Metropolitan Area of São Paulo (MASP), a megacity with about 21 million inhabitants. The measurements were carried out from 20 December 2016 to 15 March 2017. The chemical composition was measured with an Aerodyne Aerosol Chemical Speciation Monitor and size distribution with a TSI Scanning Mobility Particle Sizer 3082. PM1 mass concentrations in the MASP had an average mass concentration of 11.4 µg m−3. Organic aerosol (OA) dominated the PM1 composition (56 %), followed by sulfate (15 %) and equivalent black carbon (eBC, 13 %). Four OA classes were identified using positive matrix factorization: oxygenated organic aerosol (OOA, 40 % of OA), biomass burning organic aerosol (BBOA, 13 %), and two hydrocarbon-like OA components (a typical HOA related to vehicular emissions (16 %) and a second HOA (21 %) representing a mix of anthropogenic sources). Particle number concentrations averaged 12 100±6900 cm−3, dominated by the Aitken mode. The accumulation mode increased under relatively high-PM1 conditions, suggesting an enhancement of secondary organic aerosol (SOA) production. Conversely, the contribution of nucleation-mode particles was less dependent on PM1 levels, consistent with vehicular emissions. The relationship between aerosol size modes and PM1 composition was assessed by multilinear regression (MLR) models. Secondary inorganic aerosols were partitioned between Aitken and accumulation modes, related to condensation particle growth processes. Submicron mass loading in the accumulation mode was mostly associated with highly oxidized OOA and also traffic-related emissions. To the authors' knowledge, this is the first work that uses the MLR methodology to estimate the chemical composition of the different aerosol size modes. The chemical composition with size-dependent PM provides innovative information on the properties of both primary and secondary organic aerosols, as well as inorganic aerosols in a complex urban environment. The results emphasize the relevance of vehicular emissions to the air quality at MASP and highlight the key role of secondary processes on the PM1 ambient concentrations in the region since 56 % of PM1 mass loading was attributed to SOA and secondary inorganic aerosol.

Measurement report: Fourteen months of real-time characterisation of the submicronic aerosol and its atmospheric dynamics at the Marseille–Longchamp supersite

Abstract. This study reports results of PM1 chemical composition determined using a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) over a 14-month period (1 February 2017–13 April 2018) at the Marseille–Longchamp supersite (MRS-LCP) in France. Parallel measurements were performed with an aethalometer, an ultrafine particle monitor and a suite of instruments to monitor regulated pollutants (PM2.5, PM10, NOx, O3 and SO2). The average PM1 chemical composition over the period was dominated by organic aerosol (OA; 49.7 %) and black carbon (BC; 17.1 %), while sulfate accounted for 14.6 %, nitrate for 10.2 %, ammonium for 7.9 % and chloride for 0.5 % only. Wintertime was found to be the season contributing the most to the annual PM1 mass concentration (30 %), followed by autumn (26 %), summer (24 %) and spring (20 %). During this season, OA and BC concentrations were found to contribute 32 % and 31 % of their annual concentrations, respectively, as a combined result of heavy urban traffic, high emissions from residential heating and low planetary boundary layer (PBL) height. Most (75 %) of the 15 days exceeding the target daily PM2.5 concentration value recommended by the World Health Organization (WHO) occurred during this season. Local and long-range pollution episodes with contrasting chemical composition could be distinguished, accounting for 40 % and 60 % of the exceedance days, respectively. Enhanced OA and BC concentrations, mostly originating from domestic wood burning under nocturnal land breeze conditions, were observed during local pollution episodes, while high levels of oxygenated OA and inorganic nitrate were associated with medium-/long-range transported particles. In summertime, substantially higher concentrations of sulfate were found, with an average and a maximum contribution to the PM1 mass of 24 % and 66 %, respectively. Results from k-means clustering analysis of daily profiles of sulfate concentrations clearly reveal the significant influence of local harbour/industrial activities on air quality in addition to the more regional contribution of shipping traffic that originates from the Mediterranean basin.

Site-specific variation in mass concentration and chemical components in ambient nanoparticles (PM0.1) in North Sumatra Province-Indonesia

In this study, as the first step in mitigating contamination by PM0.1, particles with diameters less than 0.1 μm, the current air pollution situation in Indonesia was investigated with respect to particulate matter (PM), especially regarding the status and characteristics of PM0.1. Air sampling in different size ranges down to PM0.1 was conducted at roadsides, at a school adjacent to a road, an industrial area and an area near a volcano in North Sumatera Province. Analyses were conducted for carbonous components (OC, EC, TC, WSOC and WISOC), and ions including oxalate in the PM0.1 fraction. We identified PM2.5 and PM10 mass concentrations in the area of the city that exceeded WHO guidelines. From the chemical components in the PM0.1 fraction, we found that WISOC, NO3− and soot-EC were the most common components, suggesting that local traffic is a contributor and another group consisting of K+, SO42− and WSOC suggesting the occurrence of biomass burning related to local industrial and rural sources.

Assessment of near-surface air pollutants at an urban station over the central Indo-Gangetic Basin: Role of pollution transport pathways

The assessment of near-surface air pollutants has been done at an urban site, Varanasi, in the central Indo-Gangetic Basin (IGB) during July 2014 to June 2018. The various pollutants, such as particulate matters of diameter less than 2.5 μm (PM2.5) and less than 10 μm (PM10), sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) were obtained from the Central Pollution Control Board (CPCB). The annual mean mass concentrations of PM10, PM2.5, SO2, NO2 and O3 were 239 ± 128, 123 ± 89, 17.5 ± 9.6, 52 ± 35 and 30 ± 14 μg m−3, respectively. The concentrations of PM10, PM2.5 and NO2 were found to be higher than their National Ambient Air Quality Standards (NAAQS) by a factor of 4, 3.1 and 1.3, respectively; however, SO2 and O3 were always well within their standard limits. Seasonally, all the pollutants, except ozone were found to be the highest during the postmonsoon and winter seasons. The sources of pollutants have been widely characterized at this site and in general over the IGB. Further, an attempt has been made, for the first time, to elucidate the possible transport pathways of the measured pollutants, especially PM2.5 to downwind of the station using concentration weight trajectory (CWT) analyses with the forward air mass trajectories. The results show significant potential for transport of PM2.5 (~ 65%) from the IGB to downwind over the northern Bay of Bengal region, with more pronounced during the winter season (~ 95%). These results underline the importance of IGB pollution outflow towards downwind continental and marine regions, which can have significant climatic impacts.

Variations of radon and airborne particulate matter near three large phosphogypsum stacks in Florida.

Approximately 1 billion tons of phosphogypsum (PG), a by-product of the fertilizer industry, are currently stacked in Florida. PG emits radon gas, which is a risk factor for lung cancer and can also increase particulate matter (PM) associated non-cancer mortality in exposed individuals. We measured concentrations of atmospheric radon and particulate matter near PG stacks and their short-term variations at different distances to estimate exposures in nearby communities. Specifically, we measured atmospheric levels of radon, and mass concentrations of PM1, PM2.5, and PM10, and number concentrations of PM0.3, PM0.5, PM1, PM2.5, PM5, and PM10 near three large PG stacks in Florida. Atmospheric radon was collected at distances of 2.5, 5.0, and 7.5 miles downwind from three large PG stacks using charcoal-based kits and measured by liquid scintillation counting. A professional radon monitor was used to take 24-h-average radon reading at 5.0 miles from each stack for comparison purposes. The median (IQR) radon levels were 0.325 (0.150, 0.675), 0.150 (0.150, 0.650), and 0.500 (0.150, 0.700) pCi/L at 2.5, 5, and 7.5 miles, respectively. The median (IQR) PM2.5 levels were 5 (4, 6), 5 (3, 7), and 5 (2, 9) µg/m3 at 2.5, 5, and 7.5 miles, respectively. Non-parametric Kruskal-Wallis test could not detect any association between radon or PM levels and distances (2.5-7 miles) from PG stacks. With scintillation counting, median radon levels detected were above the US Environmental Protection Agency (EPA) recommended standard in some of the sites; however, much higher levels were detected through the more advanced digital monitor. PM2.5 levels were below the US-EPA 24-h average national ambient air quality standard in the study area. We conclude that ambient radon levels near PG stacks could exceed US EPA recommended outdoor standards and do not vary within a short distance from the sources, implying similar exposures in nearby communities.

Semi-outdoor filterless air purifier for smog and microbial protection with water purifier system

PurposeAir pollution and COVID-19 problems are being increasingly scrutinized. This article discusses the optimum design of an indoor and semi-outdoor air purifier, using a water-based filtration system. MethodsAn air purifier was fabricated, then comparison of purifying efficacy of the system between untreated air and using an air pump was done. Incense smoke was generated within a room for 10 seconds. The number of particle sizes of PM0.3, PM0.5, PM1.0, PM3.0, PM5.0, and PM10 μm (particle/ m3) as well as the detection of mass concentration of PM1.0, PM2.5, PM5.0, and PM10 (mg/m3) at 0 and 5 min were recorded. Each experiment was repeated 10 times. ResultsParticles in untreated air, except PM10, showed the maximum increase rate of the number of particle sizes greater than the air pump experiment. The highest differentiation between two methods was that PM1.0 and PM0.5 of untreated air increased to 113.647 and 61.539 % whereas the air pump method showed 4.720 and 2.533 %, respectively. The PM mass concentration of untreated air increased from 50.217 to 51.167 % while the increased rate of PM using an air pump was 2.784 to 2.902 %. ConclusionThis study proposed a water-based air filtration technique, which can reduce the level of particulate matter, and also is a low-cost prototype. For the next experiment, the study should extend test length, clarify an optimum ratio of disinfectant technologies, connect with the internet of things, compare the efficiency with a HEPA filter air purifier, and then also measure some particles which are smaller than 0.2 μm.

Characteristics of Chemical Speciation in PM1 in Six Representative Regions in China.

A better knowledge of aerosol properties is of great significance for elucidating the complex mechanisms behind frequently occurring haze pollution events. In this study, we examine the temporal and spatial variations in both PM1 and its major chemical constituents using three-year field measurements that were collected in six representative regions in China between 2012 and 2014. Our results show that both PM1 and its chemical compositions varied significantly in space and time, with high PM1 loadings mainly observed in the winter. By comparing chemical constituents between clean and polluted episodes, we find that the elevated PM1 mass concentration during pollution events should be largely attributable to significant increases in organic matter (OM) and inorganic aerosols like sulfate, nitrate, and ammonium (SNA), indicative of the critical role of primary emissions and secondary aerosols in elevating PM1 pollution levels. The ratios of PM1/PM2.5 are found to be generally high in Shanghai and Guangzhou, while relatively low ratios are seen in Xi’an and Chengdu, indicating anthropogenic emissions were more likely to accumulate in forms of finer particles. With respect to the relative importance of chemical components and meteorological factors quantified via statistical modeling practices, we find that primary emissions and secondary aerosols were the two leading factors contributing to PM1 variations, though meteorological factors also played important roles in regulating the dispersion of atmospheric PM.

Evaluations of Surface PM10 Concentration and Chemical Compositions in MERRA-2 Aerosol Reanalysis over Central and Eastern China

The chemical composition dataset of Aerosol Reanalysis of NASA’s Modern-Era Retrospective Analysis for Research and Application, version 2 (MERRAero) has not been thoroughly evaluated with observation data in mainland China due to the lack of long-term chemical components data. Using the 5-year data of PM10 mass concentrations and chemical compositions obtained from the routine sampling measurements at the World Meteorological Organization the Global Atmosphere Watch Programme regional background stations, Jing Sha (JS) and Lin’An (LA), in central and eastern China, we comprehensively evaluate the surface PM10 concentrations and chemical compositions such as sulfate (SO42−), organic carbon (OC) and black carbon (BC) derived from MERRAero. Overall, the concentrations of PM10, SO42−, OC and BC from the MERRAero agreed well with the measurements, despite a slight and consistent overestimation of BC concentrations and a moderate and persistent underestimation of PM10 concentrations throughout the study period. The MERRAero reanalysis of aerosol compositions performs better during the summertime than wintertime. By considering the nitrate particles in PM10 reconstruction, MERRAero performance can be significantly improved. The unreasonable seasonal variations of PM10 chemical compositions at station LA by MERRAero could be causative factors for the larger MERRAero discrepancies during 2016–2017 than the period of 2011–2013.

Air pollution levels near crossroads with different traffic density and the estimation of health risk.

The aim of this study was to determine the influence of traffic density on air pollutant levels as well as to analyse the spatial and temporal distribution of particulate pollutants and their health risk. The following species related to traffic pollution were measured: PM10, elemental and organic carbon and polycyclic aromatic hydrocarbons (PAHs) in PM10 and gas pollutants (SO2, NO2 and CO). The measurements were carried out at four crossroad sites in the city. Samples of PM10 were collected over three periods (6 am to 2pm, 2pm to 10pm and 10pm to 6 am) on working days and weekends. Statistically significant differences were found between sampling sites for all pollutant concentrations, except for NO2. The highest mass concentrations of PM10, carbon and PAHs were observed in the south of the city with the highest traffic density. Concentrations of gasses (CO and NO2) showed high values in morning and in the late afternoon and evening (west and east). At all measuring sites, the highest concentration of particle-bound pollutants was mostly recorded during morning and afternoon, except at the south, where elevated PAHs concentrations were recorded during night period, which indicated that residential heating takes up a portion of pollution sources in this area. Although for most of the pollutants the concentrations varied during the day, statistically significant differences between sampling periods were not found. The highest health risk was obtained at the south, where it was scored as significant.

Microphysics of fog bursting in polluted urban air

The goal of this work is to study sudden fog visibility (Vis) changes called fog bursting occurred during polluted urban air conditions. Fog bursting refers to a sudden drop of fog Vis below 500 m over 30 min. A comprehensive field observational campaign called Costal City Fog Microphysical Research (CCFMR) was carried out over the city of Tianjin, China during winter of 2016–2017. The six fog bursting cases occurred during the project suggest that droplet number concentration (Nd) and liquid water content (LWC) were higher than these of other conditions. The mass concentration of PM2.5 (NPM2.5) was also higher before the fog bursting events. The fog droplet spectra (FDS) followed a Junge distribution. During fog bursting events, Vis, surface air temperature (Ta) and dew point depression (Ta-Td) exhibited decreasing trends. On the other hand, mean and turbulence kinetic energy (MKE and TKE), as well as friction velocity (u∗) had increasing trends in time. After the fog bursting, environment stability changed from the neutral stage to weakly unstable stage, and fog became deeper and optically thicker. The FDS broadened drastically between 20 and 35 μm diameter, and smaller Nd increased up to 1 order of magnitude. It is concluded that fog bursting is positively affected by combination of decreasing Ta by radiative cooling, increasing RH, turbulence mixing, and high value of NPM2.5. Results from this work suggest that fog bursting conditions need to be studied in detail by numerical weather forecast (NWP) models that currently lack of these conditions.