Secondary Inorganic Aerosols Research Articles

Investigation of the influence of mineral dust on airborne particulate matter during the COVID-19 epidemic in spring 2020 over China

A regional air quality model system (RAQMS) driven by the Weather Research and Forecasting model (WRF) is applied to investigate the distribution and evolution of mineral dust and anthropogenic aerosols over China in April 2020, when air quality was improved due to reduced human activity during the COVID-19 epidemic, whereas dust storms began to attack China and deteriorated air quality. A dust deflation model was developed and improved mineral dust prediction. Model validation demonstrated that RAQMS was able to reproduce PM10, PM2.5 and aerosol components reasonably well. China suffered from three dust events in April 2020, with the maximum hourly PM10 concentrations exceeding 700 μg m−3 in downwind cities over the North China Plain (NCP). Mineral dust dominated PM10 mass (>80%) over the Gobi deserts in north and west China, while it comprised approximately 30–50% of PM10 over wide areas of east China. The domain and monthly mean dust mass fractions in PM10 were estimated to be 47% and 43% over the North China Plain and east China, respectively. On average, mineral dust contributed up to 22% and 21% of PM2.5 mass over the North China Plain and east China in April 2020, respectively. Sulfate and nitrate produced by heterogeneous chemical reactions on dust surface accounted for approximately 9% and 13% of secondary inorganic aerosols (SIA) concentration over the North China Plain and east China, respectively. The results from this study demonstrated that mineral dust made an important contribution to particulate matter mass during the COVID-19 epidemic in spring 2020 over China.

Atmospheric pollutants response to the emission reduction and meteorology during the COVID-19 lockdown in the north of Africa (Morocco).

Climate and air quality change due to COVID-19 lockdown (LCD) are extremely concerned subjects of several research recently. The contribution of meteorological factors and emission reduction to air pollution change over the north of Morocco has been investigated in this study using the framework generalized additive models, that have been proved to be a robust technique for the environmental data sets, focusing on main atmospheric pollutants in the region including ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), particulate matter (PM2.5 and PM10), secondary inorganic aerosols (SIA), nom-methane volatile organic compounds and carbon monoxide (CO) from the regional air pollution dataset of the Copernicus Atmosphere Monitoring Service. Our results, indicate that secondary air pollutants (PM2.5, PM10 and O3) are more influenced by metrological factors and the other air pollutants reported by this study (NO2 and SO2). We show a negative effect for PBHL, total precipitation and NW10M on PM (PM2.5 and PM10), this meteorological parameters contribute to decrease in PM2.5 by 9, 2 and 9% respectively, before LCD and 8, 1 and 5% respectively during LCD. However, a positive marginal effect was found for SAT, Irradiance and RH that contribute to increase PM2.5 by 9, 12 and 18% respectively, before LCD and 17, 54 and 34% respectively during LCD. We found also that meteorological factors contribute to O3, PM2.5, PM10 and SIA average mass concentration by 22, 5, 3 and 34% before LCD and by 28, 19, 5 and 42% during LCD respectively. The increase in meteorological factors marginal effect during LCD shows the contribution of photochemical oxidation to air pollution due to increase in atmospheric oxidant (O3 and OH radical) during LCD, which can explain the response of PM to emission reduction. This study indicates that PM (PM2.5, PM10) has more controlled by SO2 due to the formation of sulfate particles especially under high oxidants level. The positive correlation between westward wind at 10 m (WW10M), Northward Wind at 10 m (NW10M) and PM indicates the implication of sea salt particles transported from Mediterranean Sea and Atlantic Ocean. The Ozone mass concentration shows a positive trend with Irradiance, Total and SAT during LCD; because temperature and irradiance enhance tropospheric ozone formation via photochemical reaction.This study shows the contribution of atmospheric oxidation capacity to air pollution change.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00477-022-02224-z.

Spatial and Temporal Variations in the Atmospheric Age Distribution of Primary and Secondary Inorganic Aerosols in China

The aging timescale of particles is a key parameter in determining their impacts on air quality, human health, and climate. In this study, a one-year simulation of the age distributions of the primary and secondary inorganic fine particulate matter (PM2.5) components was conducted over China using an age-resolved Community Multiscale Air Quality (CMAQ) model. The results indicate that primary PM2.5 (PPM) and ammonium mainly originate from fresh local emissions, with approximately 60%–80% concentrated in 0–24 h age bins in most of China throughout the year. The average age is about 15–25 h in most regions in summer, but increases to 40–50 h in southern region of China and the Sichuan Basin (SCB) in winter. Sulfate is more aged than PPM, indicating an enhanced contribution from regional transport. Aged sulfate with atmospheric age > 48 h account for 30%–50% of total sulfate in most regions and seasons, and the concentrations in the > 96 h age bin can reach up to 15 µg·m−3 in SCB during winter. Dramatic seasonal variations occur in the Yangtze River Delta, Pearl River Delta, and SCB, with highest average age of 60–70 h in winter and lowest of 40–45 h in summer. The average age of nitrate is 20–30 h in summer and increases to 40–50 h in winter. The enhanced deposition rate of nitric acid vapor combined with the faster chemical reaction rate of nitrogen oxides leads to a lower atmospheric age in summer. Additionally, on pollution days, the contributions of old age bins (> 24 h) increase notably for both PPM and secondary inorganic aerosols in most cities and seasons, suggesting that regional transport plays a vital role during haze events. The age information of PM2.5, provided by the age-resolved CMAQ model, can help policymakers design effective emergent emission control measures to eliminate severe haze episodes.

The pathway of impacts of aerosol direct effects on secondary inorganic aerosol formation.

Airborne aerosols reduce surface solar radiation through light scattering and absorption (aerosol direct effects, ADEs), influence regional meteorology, and further affect atmospheric chemical reactions and aerosol concentrations. The inhibition of turbulence and the strengthened atmospheric stability induced by ADEs increases surface primary aerosol concentration, but the pathway of ADE impacts on secondary aerosol is still unclear. In this study, the online coupled meteorological and chemistry model (WRF-CMAQ; Weather Research and Forecasting-Community Multiscale Air Quality) with integrated process analysis was applied to explore how ADEs affect secondary aerosol formation through changes in atmospheric dynamics and photolysis processes. The meteorological condition and air quality in the Jing-Jin-Ji area (denoted JJJ, including Beijing, Tianjin, and Hebei Province in China) in January and July 2013 were simulated to represent winter and summer conditions, respectively. Our results show that ADEs through the photolysis pathway inhibit sulfate formation during winter in the JJJ region and promote sulfate formation in July. The differences are attributed to the alteration of effective actinic flux affected by single-scattering albedo (SSA). ADEs through the dynamics pathway act as an equally or even more important route compared with the photolysis pathway in affecting secondary aerosol concentration in both summer and winter. ADEs through dynamics traps formed sulfate within the planetary boundary layer (PBL) which increases sulfate concentration in winter. Meanwhile, the impact of ADEs through dynamics is mainly reflected in the increase of gaseous-precursor concentrations within the PBL which enhances secondary aerosol formation in summer. For nitrate, reduced upward transport of precursors restrains the formation at high altitude and eventually lowers the nitrate concentration within the PBL in winter, while such weakened vertical transport of precursors increases nitrate concentration within the PBL in summer, since nitrate is mainly formed near the surface ground.

Measurement report: Characterization and source apportionment of coarse particulate matter in Hong Kong: insights into the constituents of unidentified mass and source origins in a coastal city in southern China

Abstract. Coarse particulate matter (i.e. PM with an aerodynamic diameter between 2.5 and 10 µm – PM2.5 and PM10 – or PMcoarse) has been increasingly recognized for its importance in PM10 regulation because of its growing proportion in PM10 and the accumulative evidence for its adverse health impact. In this work, we present comprehensive PMcoarse speciation results obtained through a 1-year-long (January 2020–February 2021) joint PM10 and PM2.5 chemical speciation study in Hong Kong, a coastal and highly urbanized city in southern China. The annual average concentration of PMcoarse is 14.9 ± 8.6 µg m−3 (± standard deviation), accounting for 45 % of PM10 (32.9 ± 18.5 µg m−3). The measured chemical components explain ∼75 % of the PMcoarse mass. The unexplained part is contributed by unmeasured geological components and residue liquid water content, supported through analyses by positive matrix factorization (PMF) and the thermodynamic equilibrium model ISORROPIA II. The PMcoarse mass is apportioned to four sources resolved by PMF, namely soil dust/industrial and coal combustion, construction dust/copper-rich emissions, fresh sea salt, and an aged sea salt factor containing secondary inorganic aerosols (mostly nitrate). The PMcoarse concentration and source composition exhibit a distinct seasonal variation, a result mainly driven by the source areas the air masses have travelled through as revealed by back-trajectory analysis. In summer when the site is dominated by marine air mass, PMcoarse is the lowest (average = 8.1 µg m−3) and sea salt the largest contributor (47 %), followed by the two dust factors (36 % in total). In winter when the site receives air mass mainly from the northern continental region, PMcoarse concentration triples (24.8 µg m−3), with the two dust factors contributing three quarters of the aerosol mass. The potential dust source areas are mapped using the concentration-weighted trajectory technique, showing either the Greater Bay Area or the greater part of southern China as the origin of fugitive dust emissions leading to elevated ambient PMcoarse loadings in Hong Kong. This study, the first of this kind in our region, provides highly relevant guidance for other locations with similar monitoring needs. Additionally, the study findings point to the need for further research on the sources, transport, aerosol processes, and health effects of PMcoarse.

Chemical characteristics and source apportionment of particulate matter (PM2.5) in Dammam, Saudi Arabia: Impact of dust storms

Atmospheric particulate matter (PM) is known to be harmful to human and environmental health, with factors including particle size and composition thought to be key drivers of toxicity. Understanding the composition and hence sources of PM is critical to distinguish between anthropogenic and natural impacts, and develop the most efficient air pollution mitigation policies. This distinction is particularly important in areas affected by dust storm activity from nearby arid regions, which may dominate long-term PM mass concentrations. In this work, 24-hour PM 2.5 samples were collected from two locations in Dammam city, Saudi Arabia during the winter and summer of 2018, and subjected to detailed analysis to assess the PM characteristics and sources. Offline chemical analysis of the samples utilied ICP/MS, ion chromatography and thermal decomposition for measurement of trace metals, ions and OC/EC concentrations, respectively. Positive Matrix Factorization (PMF) analyses were used to identify sources of PM 2.5 in Dammam. The mean PM 2.5 mass concentration in the summer was twice that in the winter at both locations, and crustal and secondary inorganic aerosol components dominated over other species in determining PM 2.5 mass concentrations at both seasons and locations. The PMF analysis identified six source factors, including crustal, nitrate-rich, sea salt, sulfate-rich, biomass burning and traffic sources. In addition, the impact of dust storms on PM 2.5 concentrations was analysed. Dust storms increased the 24-hour average concentration of PM 2.5 by three-fold, and that of crustal elements by five-fold while the impact of dust storms on components identified as anthropogenic in origin was limited. Overall, dust-storm activity accounted for 42% of PM 2.5 mass concentration; after accounting for this aspect, secondary inorganic components derived largely from primary pollutant emissions dominated the remaining PM 2.5 mass. • Comprehensive assessment of PM 2.5 composition and sources in Dammam, Saudi Arabia. • Average 24-hour PM 2.5 mass concentrations ranged from 54 to 121 ug/m 3 . • Dominant components found to be crustal elements, metals, organic and inorganic carbon. • Anthropogenic sources accounted for 40% of PM 2.5 mass, rising to 58% if dust storm periods were excluded. • These results highlight emissions control priorities to improve air quality in Saudi Arabia.

Transboundary aerosol transport process and its impact on aerosol-radiation-cloud feedbacks in springtime over Northeast Asia

Northeast Asia has been suffering from dramatic increases of particulate matter (PM) since the late 1990s, and it still continues to undergo haze despite various abating regulations. In this study, we investigated aerosol-cloud-precipitation (ACP) interactions with the varied PM, and the impact of long-range transport (LRT) process on ACP in springtime was assessed in Northeast Asia. Our long-term (1995–2019) analysis of PM10 exhibited the correlation with decreases of both sunshine duration and drizzle occurrences that can be interpreted as direct and indirect aerosol effects, while cloud cover induced by the varied PM10 was found only in more than 90% cloud cover (9/10–10/10 category). The online WRF-Chem with wind-blown dust simulation indicated that cloud water was affected by secondary inorganic aerosol (SIA) formation near the surface in upwind areas dominantly, whereas, along the LRT pathway, cloud water perturbation altitudes were increased quasi-linearly toward downward between 1 and 3 km. The gas-to-particle conversion ratios of sulfur ([SO42−]/[SO2 + SO42−]) and nitrogen ([NO3−]/[NO2 + NO3−]) both remain aloft long at the same vertical levels of most perturbed cloud altitude enough to be transported over long distance in springtime. Formations of sulfate and nitrate showed different ACP interaction timing; distinctive shifts in the ratios observed at the exit (Shanghai-Yellow Sea) by nitrate, and entrance areas (Seoul-Tokyo) by sulfate along the LRT pathway, respectively, with higher ratios of 0.8 or more in springtime. Our results indicate that ACP processes have been enhanced at a LRT-related altitude with different SIA production timings that can be considered in species-specific springtime PM abatements over Northeast Asia.

Exploring the causes for co-pollution of O3 and PM2.5 in summer over North China.

Co-pollution of surface O3 and PM2.5 has become the most predominant type of air pollutions in Beijing-Tianjin-Hebei region in the hot season since 2017, particularly in May-July. Analysis based on observational data showed that co-pollution was always accompanied by high temperature, moderate relative humidity, extremely high SO2, and higher NO2. We also found that the meteorology and precursor dependence of O3 was similar between co-pollution and O3- single pollution. While PM2.5 in co-pollution was more related to temperature, relative humidity, and precursors, that in PM2.5-singe pollution were more related to small winds. These results indicate that co-pollution seemed to be more affected by atmospheric chemistry. According to the PM2.5 components, secondary inorganic aerosols (SIA) composed 44.3-48.7% of PM2.5 in co-pollution, while those accounting for 42.1-46.5% and 41.2-44.3%, respectively, in O3- and PM2.5-single pollution, which further confirmed the relatively stronger atmospheric chemistry processes in co-pollution. And the high proportion of SIA in co-pollution was mainly attributed to SO42-, which was observed to rapidly boom in non-refractory submicron aerosol (NR-PM1) on the condition of high level of O3 at daytime. Additionally, we further explored the interactions of O3 and PM2.5 in co-pollution. It was found that most (~61.9%) co-pollution episodes were initiated by high O3 at daytime; while for other episodes, high PM2.5 firstly occurred under the more stable meteorological conditions, and then accumulation of precursors further induced high O3. A higher SIA concentration was observed in O3-initiated co-pollution, indicating that the atmospheric oxidation in co-pollution caused by chemical processes was stronger than that by physical processes, which was further approved by the higher values of SOR and NOR in O3-initiated co-pollution. This observational study revealed that controlling O3 and precursor SO2 is the key to abating co-pollution in the hot season.

Rapid transition of aerosol optical properties and water-soluble organic aerosols in cold season in Fenwei Plain

The Fenwei Plain (FWP) continues to be one of the most polluted regions in China despite the improvement of air quality in recent years. However, our understanding of aerosol optical properties (AOP) and its relationship with aerosol composition particularly in cold season is far from complete. Here we conducted three-month measurements of AOP from November 2020 to January 2021 in the FWP along with fine particle composition and water-soluble organic aerosol (WSOA) measurements. Our results showed rapid transitions in AOP from November to January due to the enhanced primary emissions and the decreased aqueous-phase processing. The single scattering albedo (SSA) decreased from 0.85 to 0.78, while the absorption Ångstrӧm exponent (AAE) increased from 1.41 to 1.60, demonstrating the increasing role of absorbing aerosol and brown carbon in cold season. Further analysis showed that SSA increased significantly with the fraction of secondary inorganic aerosol, while AAE was highly correlated with the fraction of primary OA (POA), highlighting the different impacts of primary and secondary aerosol on AOP. Chemical apportionment showed the dominant contributions of ammonium nitrate (29%) and ammonium sulfate (27%) to particle extinction before heating season, while that of POA increased to 27% during heating season. Although the pollution level showed a clear increase during the heating season, the changes in visibility were small due to the decreased mass extinction efficiency from 3.48 to 2.91 m2 g−1. Positive matrix factorization illustrated a clear transition in WSOA composition from the dominance of secondary OA (SOA) in November to POA in heating season. Compared with the large decrease in water-soluble aqueous-phase SOA, the consistently high concentration of photochemical-related SOA elucidated the presence of strong photochemical processing in cold season. Overall, our results demonstrate the significant transition in primary emissions and secondary formation in cold season, and such changes have affected AOP substantially.

Effect of vehicle fleet composition and mobility on outdoor population exposure: A street resolution analysis in Paris

High concentrations of health-related pollutants are observed in streets, inducing high outdoor population exposure. The impact of reducing traffic emissions on urban air quality is often quantified using regional-scale chemical-transport models (CTMs), which are representative of background concentrations but fail to represent the high street concentrations. Local-scale models may be more suitable to represent them, but their use for outdoor exposure assessments is still limited, because they often neglect secondary species, use simplified methods to estimate background concentrations, and omit/underestimate non-exhaust emissions. Here the impact of realistic and ambitious tendencies of vehicle fleet renewal and mobility on outdoor population exposure is investigated using multi-scale simulations. They are capable of representing secondary species in urban background and streets (including the formation of secondary organic and inorganic aerosols), and use non-exhaust emissions determined with a recently revisited approach. The 10-year vehicle fleet renewal induces large decreases in population exposure to NO2, black carbon, PM10, PM2.5, and organics. These decreases are stronger than estimated using CTMs. Favouring recent diesel, petrol, or electric vehicles, as proposed here, induces similar decreases of outdoor population exposure to PM2.5. Promoting electric vehicles induces the highest decrease of exposure to NO2. Home-office practice enhances the decrease of pollutant concentrations, but it is less effective than vehicle fleet renewal. However, much more ambitious reductions of pollutant emissions are still needed to respect air-quality guidelines.

Secondary Organic and Inorganic Aerosol Formation from a GDI Vehicle under Different Driving Conditions

This study investigated the primary emissions and secondary aerosol formation from a gasoline direct injection (GDI) passenger car when operated over different legislative and real-world driving cycles on a chassis dynamometer. Diluted vehicle exhaust was photooxidized in a 30 m3 environmental chamber. Results showed elevated gaseous and particulate emissions for the cold-start cycles and higher secondary organic aerosol (SOA) formation, suggesting that cold-start condition will generate higher concentrations of SOA precursors. Total secondary aerosol mass exceeded primary PM emissions and was dominated by inorganic aerosol (ammonium and nitrate) for all driving cycles. Further chamber experiments in high temperature conditions verified that more ammonium nitrate nucleates to form new particles, forming a secondary peak in particle size distribution instead of condensing to black carbon particles. The results of this study revealed that the absorption of radiation by black carbon particles can lead to changes in secondary ammonium nitrate formation. Our work indicates the potential formation of new ammonium nitrate particles during low temperature conditions favored by the tailpipe ammonia and nitrogen oxide emissions from gasoline vehicles.

Year-round observation of atmospheric inorganic aerosols in urban Beijing: Size distribution, source analysis, and reduction mechanism

To investigate particle characteristics and find an effective measure to control severe particle pollution, year-round observation of size-segregated inorganic aerosols was conducted in Beijing from January to December, 2016. The sampled atmospheric particles all presented bimodal size distribution at four pollution levels (clear, slight pollution, moderate pollution and severe pollution), and peak values appeared at the size range of 0.7-2.1 μm and >9.0 μm, respectively. As dominant particle compositions, NO3−, SO42−, and NH4+ in four pollution levels all showed significant peaks in fine mode, especially at the size range of 1.1-2.1 μm. Secondary inorganic aerosols accounted for about 67.6% (36.3% (secondary sulfates) + 31.3% (secondary nitrates)) of the total sources of fine particles in urban Beijing. Severe pollution of fine particles was mainly caused by the air masses transported from nearby western and southern areas, which are industrial and densely populated region, respectively. Sensitivity tests further revealed that the control measures focusing on ammonium emission reduction was the most effective for particle pollution mitigation, and fine particles all showed nonlinear responses after reducing ammonium, nitrate, and sulfate concentrations, with the fitting curves of y = -120.8x - 306.1x2 + 290.2x3, y = -43.5x - 67.8x2, and y = -25.8x - 110.4x2 + 7.6x3, respectively (y and x present fine particle mass variation (μg/m3) and concentration reduction ratio (CRR)/100 (dimensionless)). Overall, our study presents useful information for understanding the characteristics of atmospheric inorganic aerosols in urban Beijing, as well as offers policy makers with effective measure for mitigating particle pollution.

Significant contribution of secondary particulate matter to recurrent air pollution: Evidence from in situ observation in the most polluted city of Fen-Wei Plain of China

Particulate matter (PM) pollution in high emission regions will affect air quality, human health and climate change on both local and regional scales, and thus attract worldwide attention. In this study, a comprehensive study on PM2.5 and its chemical composition were performed in Yuncheng (the most polluted city of Fen-Wei Plain of China) from November 28, 2020 to January 24, 2021. The average concentration of PM2.5 was 87.8 ± 52.0 μg/m3, which were apparently lower than those observed during the same periods of past five years, attributable to the clean air action plan implemented in this region. NO3− and organic carbon (OC) were the dominant particulate components, which on average contributed 22.6% and 16.5% to PM2.5, respectively. The fractions of NO3−, NH4+, OC and trace metals increased while those of crustal materials and elemental carbon decreased with the degradation of PM2.5 pollution. Six types of PM2.5 sources were identified by the PMF model, including secondary inorganic aerosol (35.3%), coal combustion (28.7%), vehicular emission (20.7%), electroplating industry (8.6%), smelt industry (3.9%) and dust (2.8%). Locations of each identified source were pinpointed based on conditional probability function, potential source contribution function and concentration weighted trajectory, which showed that the geographical distribution of the sources of PM2.5 roughly agreed with the areas of high emission. Overall, this study provides valuable information on atmospheric pollution and deems beneficial for policymakers to take informed action to sustainably improve air quality in highly polluted region.

Source apportionment of carbonaceous aerosols using hourly data and implications for reducing PM2.5 in the Pearl River Delta region of South China

Ambient fine particulate matter (PM2.5) levels in South China have been decreasing in the past decade, but the decreasing rates differed between its major chemical components, e.g., with much small rates for carbonaceous aerosols than for secondary inorganic aerosols. To investigate the sources of carbonaceous aerosols in this region, a comprehensive campaign was carried out in urban Guangzhou in the winter of 2019–2020 using a combination of various instruments. Data generated from this campaign include hourly total carbon (TC), black carbon (BC), criteria air pollutants and meteorological parameters, 4-hourly particle-bound elements, and chemically-resolved daily PM2.5. Similar diurnal patterns were observed for TC, CO and NO2, suggesting TC was very likely related to vehicle exhaust emission. Secondary organic carbon (SOC) estimated using the Minimum R squared (MRS) method accounted for 35 ± 17% of OC, indicating strong atmospheric oxidation capacity. Four major source factors for carbonaceous aerosols were identified by positive matrix factorization (PMF) model, including coal combustion, traffic emissions, soil dust and ship emissions, which accounted for 37 ± 23%, 39 ± 23%, 14 ± 10% and 10 ± 13%, respectively, of TC mass concentration, 38 ± 24%, 38 ± 23%, 14 ± 10% and 10 ± 12%, respectively, of OC mass concentration, and 29 ± 21%, 43 ± 22%, 14 ± 11% and 14 ± 15%, respectively, of EC mass concentration. Among these sources, traffic emission was the most important one, suggesting the necessity for promoting clean energy vehicles and relieving urban traffic congestion.

Bimodal distribution of size-resolved particle effective density: results from a short campaign in a rural environment over the North China Plain

Abstract. Effective density is one of the most important physical properties of atmospheric particles. It is closely linked to particle chemical composition and morphology and could provide special information on particle emissions and aging processes. In this study, size-resolved particle effective density was measured with a combined differential mobility analyzer–centrifugal particle mass analyzer–condensation particle counter (DMA–CPMA–CPC) system in autumn 2019 as part of the Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN). With a newly developed flexible Gaussian fit algorithm, frequent (77 %–87 %) bimodal distribution of particle effective density is identified, with a low-density mode (named sub-density mode) accounting for 22 %–27 % of the total number of observed particles. The prevalence of the sub-density mode is closely related to fresh black carbon (BC) emissions. The geometric mean for the main density mode (ρ‾eff,main) increases from 1.18 ± 0.10 g cm−3 (50 nm) to 1.37 ± 0.12 g cm−3 (300 nm) due to a larger fraction of high-density components and a more significant restructuring effect at large particle sizes but decreases from 0.89 ± 0.08 g cm−3 (50 nm) to 0.62 ± 0.12 g cm−3 (300 nm) for the sub-density mode (ρ‾eff,sub), which could be mainly ascribed to the agglomerate effect of BC. ρ‾eff,main and ρ‾eff,sub show similar diurnal cycles with peaks in the early afternoon, mainly attributed to the increasing mass fraction of high material density components associated with secondary aerosol production, especially of secondary inorganic aerosol (SIA). To investigate the impact of chemical composition, bulk particle effective density was calculated based on measured chemical composition (ρeff,ACSM) and compared to the average effective density at 300 nm (ρ‾eff,tot,300nm). The best agreement between the two densities is achieved when assuming a BC effective density of 0.60 g cm−3. The particle effective density is highly dependent on SIA and BC mass fractions. The influence of BC on the effective density is even stronger than SIA, implying the importance and necessity of including BC in the estimate of effective density for ambient particles.

Chemical characteristics of PM2.5 during spring and fall at two sites in Chungcheongnam-do, South Korea; insight into Fe solubility and SO42− formation

24-hr integrated PM2.5 were measured at two sites (Seosan and Asan) in Chungcheongnam-do, South Korea, during both spring and fall, with the following three objectives; i) to investigate the major chemical components driving PM2.5 pollution episodes and their formation processes, ii) to identify possible factors controlling aerosol Fe solubility, and iii) to examine the causes of high SO2 and SO42− measured at Asan site. The Seosan site is a place where the city, countryside, and agricultural and industrial complexes are mixed, and the Asan site is a place in which the city and industrial complexes are mixed.PM2.5 pollution episodes (>24-hr Korean PM2.5 of 35 μg/m3) during spring were dominated by local pollution, while during fall they were influenced by regional transport and local pollution. The major chemical components driving spring PM2.5 pollution episodes were NO3− for Seosan and SO42− and NO3− for Asan. On the other hand, in the fall, the increases in concentration of NO3− at both sites resulted in PM2.5 pollution episodes. During the spring and fall pollution episodes, favorable weather conditions such as low wind speed and high RH were likely an important factor for the enhanced formation of secondary inorganic aerosols. The difference in driving chemical composition leading to high PM2.5 between the two sites during pollution periods suggests that the formulation of a different control strategy is required to reduce PM2.5 concentrations at each site.Fe solubility (soluble Fe/total Fe) at Seosan and Asan were 6.2% and 5.9%, respectively, during spring, and they were 2.6% and 2.5%, respectively, during fall. Fe solubility was also enhanced during pollution episodes at both sites. The high correlations (R = 0.74–0.77) between Fe solubility and aerosol acidification [(SO42− + NO3−)/Fe] at both sites during the two seasons indicate that secondary acidic aerosol particles played a potential role in enhancing the solubility of Fe. However, Fe solubility during spring was more influenced by the acidification by SO42− particles than that by NO3− particles. Meanwhile, the opposite result was obtained for the Fe solubility during fall.The substantially increased SO42− concentration measured at the Asan site during spring was strongly associated with high SO2 emissions (∼45 ppb) from the upwind local source region and could be due to both the photochemical reaction in the afternoon and the aqueous-phase reaction between the evening and early morning hours. The results of this study suggest that reductions in SO2 and NOx emissions from local sources at the study region are absolutely required to reduce PM2.5 pollution episodes.

Synergy of multiple drivers leading to severe winter haze pollution in a megacity in Northeast China

Severe haze repeatedly shrouded Harbin during the winter of 2019–2020, making it one of the 10 most polluted cities in China for January of 2020. Here we explored the major drivers for the extreme atmospheric pollution events. Enhanced formation of secondary organic and inorganic aerosols was evident at higher pollution levels, accompanied with a sharp growth of aerosol water content (AWC) and a persistent increase of aerosol pH. Non-biomass burning (non-BB) combustion sources were inferred to be relatively stable during the measurement period. The elemental carbon mass apportioned to the non-BB sources exhibited an apparent increasing trend as aerosol concentrations became higher, pointing to the influence of unfavorable dispersion conditions. In addition, biomass burning (BB) emissions were found to be strengthened at higher aerosol concentrations. This trend was associated with a large drop of temperature, presumably indicating that the strengthened BB emissions were due to more intensive use of biomass for heating. In brief, the winter haze events in Harbin were caused by a synergy of three factors, i.e., enhanced secondary aerosol formation, unfavorable dispersion conditions and strengthened BB emissions. A semi-quantitative approach was developed to further estimate the relative importance of these drivers. Strengthened BB emissions were always less responsible for haze events compared to other factors, whereas the less severe and heavily polluted haze events were caused mainly by unfavorable dispersion conditions and enhanced secondary aerosol formation, respectively. This study provides observational evidences for efficient production of secondary species in aerosol water despite the frigid winter in Harbin, and thus highlights the need for effective control of gaseous precursors, both organic and inorganic.

Long-term residential exposure to air pollution and risk of testicular cancer in Denmark: A population-based case-control study.

The incidence rate risk of testicular cancer has increased over the last four decades, and most significant increase has been among Caucasian men in Nordic countries. Second-generation immigrant studies indicate a significant role of environmental exposure in testicular cancer. We conducted a nationwide register-based case-control study, including 6,390 testicular cancer cases registered in the Danish Cancer Registry between 1989 and 2014. Up to four age-matched controls for each case (n=18,997) were randomly selected from Civil Registration System. Ambient air pollution levels were estimated at addresses of cases and controls with a state-of-the-art air pollution modeling system. We mostly found ORs close to 1.00 and with 95% confidence intervals (CI) spanning 1.00. Exposure during the year preceding birth was associated with ORs for NO2 of 0.87 (95%CI: 0.77-0.97) per 10 µg/m3 and for organic carbon of 0.84 (95%CI: 0.72-0.98) per 1 µg/m3. Exposure during the first 10 years of life was associated with ORs for organic carbon of 0.79 (95%CI: 0.67-0.93) per 1 µg/m3, for O3 of 1.20 (95%CI: 1.07-1.34) per 10 µg/m3 and for secondary inorganic aerosols of 1.07 (95%CI: 1.00-1.15) per 1 µg/m3. Early-life exposure to NO2 and OC was associated with lower risk for testicular cancer whereas early-life exposure to O3 and SIA was associated with higher risk. We report both positive and negative associations between ambient air pollutants and risk of testicular, dependent on pollutant, exposure time window and age at diagnosis. This is the first study to investigate such associations.

Unexpected Increases of Severe Haze Pollution During the Post COVID‐19 Period: Effects of Emissions, Meteorology, and Secondary Production

AbstractUnexpectedly frequent severe haze episodes were observed in Beijing during February–March in 2021 after two phases of clean air action plan (2013–2020), yet the causes remained unclear. Here, we conducted real‐time fine particle (PM2.5) composition measurements during January–March in 2021 using a time‐of‐flight aerosol chemical speciation monitor and an aethalometer and compared with those during the coronavirus disease (COVID‐19) period in 2020. Our results showed ubiquitously elevated concentrations of chloride, black carbon (BC), and primary organic aerosol (POA) in 2021, suggesting increased primary emissions during the post‐COVID‐19 period. By using the machine learning‐based random forest (RF) algorithm, we found largely different responses of aerosol changes to meteorology in different months. After decoupling the effects of meteorology, the PM2.5 changes from 2020 to 2021 were reduced from −35.6% to −29.0% in January, −24.1% to −4.5% in February, and +92.6% to +34.2% in March, respectively. Our results demonstrate the dominant roles of stagnant meteorology and secondary production in the formation of severe haze episodes in March 2021. In particular, we found that the compositions of observed and deweathered PM2.5 were fairly similar between 2020 and 2021, and the ratios of secondary OA to secondary inorganic aerosols were close. Our study indicates that decoupling the influence of meteorological conditions is of great importance for better evaluation of mitigating strategies of air pollution due to the large impact of meteorology on the changes in PM2.5 species particularly in a short period.

Chemical significance and source apportionment of fine particles (PM2.5) in an industrial port area in East Asia

This study explored the chemical significance, seasonal variation, spatial distribution, and source apportionment of fine particles (PM2.5) in an industrial port area. 24-h PM2.5 was simultaneously sampled at three port sites. Five chemical contents in PM2.5 including water-soluble ions (WSIs), metallic elements, carbonaceous content, anhydrosugars, and organic acids were then analyzed. The source apportionment of PM2.5 was further resolved by trajectory simulation, principal component analysis (PCA), and chemical mass balance (CMB) receptor model. Both local sources and long-range transport contributed to the rise-up of PM2.5 levels. Secondary inorganic aerosols (SIAs) dominated WSIs in PM2.5. Crustal elements (Mg, Al, Ca, Fe, and K) dominated the metallic content of PM2.5, while trace elements (Ni, V, Cr, Zn, and Pb) were originated from anthropogenic sources. Ship emissions in the seaport and offshores caused high V/Ni ratios in summer. High OC/EC (2.04–2.23) and SOC/OC (28–34%) ratios were observed in fall and winter, implying the potential formation of secondary organic aerosols (SOAs) in atmosphere. High correlation of levoglucosan and K+ indicated that PM2.5 was greatly influenced by biomass burning (BB) in winter. Polluted air masses with high PM2.5 levels of 43.33 ± 11.84 μg/m3 in winter were blown from the norths by Asian Northeastern Monsoons (ANMs), while clean air masses with low PM2.5 levels of 9.13 ± 2.75 μg/m3 in summer came mainly from the oceans via Asian Southwestern Monsoons (ASMs). Source apportionment resolution showed that the dominant sources of PM2.5 in the Kaohsiung Seaport were industrial emissions, secondary aerosols (SIAs/SOAs), ship/vehicular exhausts, oceanic spray, and soil dust.