Non-haze Periods Research Articles

Quantifying the noncarcinogenic and carcinogenic risks resulting from the inhalation of PM2.5-bound metals: A multicity analysis and implications for public health

Toxic metals in PM2.5 represent a growing public health concern because of their potential health effects. Ambient PM2.5 samples were collected from five provinces around Bangkok from December 2020 to December 2021. The concentrations of PM2.5 and metals (arsenic, cadmium, chromium, cobalt, nickel, lead, and vanadium) were analyzed. The noncarcinogenic and carcinogenic risks were evaluated via Monte Carlo simulations in four age groups (0 to <6, 6 to <12, 12 to <18, 18–70 years), with a dataset comprising 2282 heavy metal assays within the particulate matter. Significantly higher PM2.5 concentrations were detected in provinces with higher factory densities, as well as higher concentrations during haze periods than during non-haze periods. The HI values for all age groups and provinces were lower than 1, indicating acceptable noncarcinogenic risks. The carcinogenic risks from PM2.5-bound metals varied between 7.08×10−7 and 4.29×10−6, indicating increased cancer risks, for preschool children and adults. Cancer risk was highest in industrial areas, followed by areas with dense traffic, and lowest in agricultural areas. The results indicated that Thailand's current air quality regulations, which primarily provide only lead limits, are insufficient considering the high carcinogenic potential of other metals. The Monte Carlo simulation results confirmed that lowering Thailand’s 24-h PM2.5 standard from 37.5 to either 25 or 15 µg m−3, as specified in the 2021 World Health Organization guidelines, would decrease cancer risk by 9.63–43.18 %.

Seasonal variation and size distribution of aromatic acids in urban aerosols in Beijing, China

Aromatic acids are an integral component of organic acids in the atmosphere, contributing to the formation of climate-altering brown carbon (BrC). To better understand the sources and formation processes of aromatic acids, we collected size-segregated particulate matter samples in urban Beijing from April 2017 to January 2018, which were analyzed using solvent-extraction followed by gas chromatography/mass spectrometry. Phthalic acid (o-PhA) had the greatest average annual concentration, followed by terephthalic acid (p-PhA), 4-hydroxybenzoic acid (4-OHBA), dehydroabietic acid (DA), syringic acid (SA), 3-hydroxybenzoic acid (3-OHBA), isophthalic acid (m-PhA), and vanillic acid (VA). We identified distinct seasonal variations in aromatic acids, with o-PhA peaking in summer due to photochemical activity, while p-PhA and 4-OHBA elevated in autumn and summer, respectively, influenced by open waste and biomass burning. Wintertime variations in all aromatic acids were driven by complex meteorology and increased anthropogenic emissions, including rural biomass burning for cooking and heating. Particle size distribution of aromatic acids was affected by seasonal agricultural activities and dust storms, multiple emission sources, and formation mechanisms. The o-PhA has predominantly bimodal distribution, with diverse sources and complex formation mechanisms including gas- and aqueous-phase chemistry. The applicability of o-PhA as a tracer for specific secondary organic aerosols has been questioned due to its potential primary sources. The 3-OHBA, 4-OHBA, VA, SA, and DA exhibited bimodal or trimodal patterns during haze and non-haze periods across different particle size ranges. The seasonal variation in VA/SA and VA/4-OHBA ratios demonstrated the complexity of biomass burning types, influenced by season, particle size, meteorological conditions, and combustion sources.

Beyond common urban air quality assessment: Relationship between PM2.5 and black carbon during haze and non-haze periods in Bangkok

The atmospheric pollution burden in Bangkok, Thailand, is likely to be similar to that of other large urban agglomerations. Black carbon (BC) aerosol is one of the key components of PM2.5 (particulate matter with equivalent diameter ≤2.5 μm) pollutants; jointly they adversely affect humans and the environment. This study assessed the BC and PM2.5 ambient concentrations in Bangkok over nine months (November 1, 2020, to July 27, 2021), focusing on seasonal differences during the haze period (Hp; december 2020 to February 2021) and non-haze period (NHP; remaining months). PM2.5 data were measured optically, together with filter sampling of particles at heights of 30, 75, and 110 m above ground level (AGL). A thermal/optical carbon analysis method was used to determine the BC mass concentrations in the collected samples. The results showed that the vertically averaged BC concentration within PM2.5 increased more than 3-fold from 2.82 to 9.09 μg/m3 from the NHP to the HP. The vertical dependence of BC concentration was characterized by an increase in the height AGL in the NHP. In contrast, the opposite trend was observed for the HP. The average values of the PM2.5/BC ratio at all heights AGL showed a seasonal trend, with the BC mass concentration accounting for over 25% of PM2.5 concentration during the peak of the haze season.

Comparing sources of carbonaceous aerosols during haze and nonhaze periods in two northern Chinese cities

Radiocarbon (14C), stable carbon isotope (13C), and levoglucosan in PM2.5 were measured in two northern Chinese cities during haze events and nonhaze periods in January 2019, to ascertain the sources and their differences in carbonaceous aerosols between the two periods. The contribution of primary vehicle emissions (17.8 ± 3.7%) to total carbon in Beijing during that haze event was higher than that of primary coal combustion (7.3 ± 4.2%), and it increased significantly (7.1%) compared to the nonhaze period. The contribution of primary vehicle emissions (4.1 ± 2.8%) was close to that of primary coal combustion (4.3 ± 3.3%) during the haze event in Xi'an, and the contribution of primary vehicle emissions decreased by 5.8% compared to the nonhaze period. Primary biomass burning contributed 21.1 ± 10.5% during the haze event in Beijing and 40.9 ± 6.6% in Xi'an (with an increase of 3.3% compared with the nonhaze period). The contribution of secondary fossil fuel sources to total secondary organic carbon increased by 29.2% during the haze event in Beijing and by 18.4% in Xi'an compared to the nonhaze period. These results indicate that specific management measures for air pollution need to be strengthened in different Chinese cities in the future, that is, controlling vehicle emissions in Beijing and restricting the use of coal and biomass fuels in winter in Xi'an.

Secondary sources of PM2.5 based on the vertical distribution of organic carbon, elemental carbon, and water-soluble ions in Bangkok

Ambient PM2.5 pollution can affect human health and the environment in global megacities. Secondary PM2.5 is produced by physical and chemical reactions of primary air pollutants. Sources of secondary PM2.5 in Bangkok have been considered in most on-target investigations for the control and management of air quality. This research aims to identify the vertical distribution of secondary PM2.5 sources in Bangkok, Thailand. Vertical distributions of PM2.5 in haze and non-haze periods were collected at different heights (30, 75, and 110 m above ground level) at the Air Pollutants Monitoring Tower, Kasetsart University (KU tower) between November 2020 and July 2021. The carbon components were analyzed by an OCEC analyzer using the IMPROVE thermal/optical reflectance (TOR) protocol, and the ionic species were determined by ion chromatography. The results showed that the organic carbon (OC) to elemental carbon (EC) ratios of PM2.5 tended to increase with altitude at 30, 75, and 110 m in the range of 2.0 - 7.7, 3.4 - 8.0 and 3.0 - 16.6, respectively. In the haze period (Jan-Feb 2021), the SOC within PM2.5 was the highest at 110 m which was 24.5%. In addition, the key components of SOC, NO3−, NH4+, and SO42− within PM2.5 were found in secondary aerosols in Bangkok. The chemical compositions indicated that secondary PM2.5 is mainly contributed by local vehicle exhaust (30 m) and long-range transported biomass burning (75 and 110 m). This research provides useful information that could be applied for urban secondary PM2.5 control and management.

Contrasting compositions of PM2.5 in Northern Thailand during La Niña (2017) and El Niño (2019) years

There have been a very limited number of systematic studies on PM2.5 compositions and their source contribution in Southeast Asia. This study aims to explore the characteristics of PM2.5 composition collected in Chiang Mai (Thailand) during La Niña and El Niño years and to apportion their sources during smoke haze and non-haze periods. The average PM2.5 concentration of smoke haze episode in 2019 (El Niño) was much higher than in 2017 (La Niña). The ratios of organic carbon (OC) to elemental carbon (EC), as well as K (biomass burning (BB) tracer) to PM2.5, were higher during smoke haze episodes in 2019 than in 2017 indicating a significant influence from BB. The ratios of secondary organic carbon (SOC) levels to primary organic carbon (POC) levels during smoke haze episodes were higher than those in non-haze period, which indicated greater SOC contributions or more photo-oxidation of precursors in haze episodes with high ambient temperatures. However, the ratios of soil markers (Ca and Mg) during non-haze period were high implying that soil source contributed more to PM2.5 concentrations when there less BB occurred. The positive Matrix Factorization (PMF) model revealed that the source of BB, characterized by high K fractions, was the largest contributor during smoke haze episodes accounting for 50% (2017) and 79% (2019). Climate conditions influence meteorological patterns, particularly during incidences of extreme weather such as droughts, which affect the scale and frequency of open burning and thus air pollution levels.

Formation mechanisms of nitrous acid (HONO) during the haze and non-haze periods in Beijing, China

As an important precursor of hydroxyl radical (OH), nitrous acid (HONO) plays a significant role in atmospheric chemistry. Here, an observation of HONO and relevant air pollutants in an urban site of Beijing from 14 to 28 April, 2017 was performed. Two distinct peaks of HONO concentrations occurred during the observation. In contrast, the concentration of particulate matter in the first period (period Ⅰ) was significantly higher than that in the second period (period Ⅱ). Comparing to HONO sources in the two periods, we found that the direct vehicle emission was an essential source of the ambient HONO during both periods at night, especially in period Ⅱ. The heterogeneous reaction of NO2 was the dominant source in period Ⅰ, while the homogeneous reaction of NO with OH was more critical source at night in period Ⅱ. In the daytime, the heterogeneous reaction of NO2 was a significant source and was confirmed by the good correlation coefficients (R2) between the unknown sources (Punknown) with NO2, PM2.5, NO2 × PM2.5 in period Ⅰ. Moreover, when solar radiation and OH radicals were considered to explore unknown sources in the daytime, the enhanced correlation of Punknown with photolysis rate of NO2 and OH (JNO2 × OH) were 0.93 in period Ⅰ, 0.95 in period Ⅱ. These excellent correlation coefficients suggested that the unknown sources released HONO highly related to the solar radiation and the variation of OH radicals.

A one-year study on black carbon in urban Beijing: Concentrations, sources and implications on visibility

A one-year field measurement was conducted at an urban atmospheric environment monitoring station in Beijing. The concentrations, sources and implications on visibility of black carbon (BC) during different periods were investigated. The average BC concentration was 2.8 ± 2.5, 3.2 ± 1.9, 4.4 ± 3.6 and 5.3 ± 4.5 μg m−3 in spring, summer, autumn and winter, respectively. The source apportionment presented liquid fuel (traffic) was the main source of BC in spring (77.4%), summer (86.8%) and autumn (70.8%), while solid fuel (coal and biomass burning) dominated in winter (64.3%), implying regional air transport occurred because of the limited combustion activities in urban Beijing. Notably, the contribution of solid fuel decreased from Ⅲ (4 ≤ Vis <6 km) to Ⅴ (0 < Vis <2 km), indicating the effect of regional air transport weakened during the wintertime severe haze pollution. Combining the results of PSCF, BC during the winter haze period was not only influenced by the air masses from southern regions but also western areas, e.g., Datong city, where coal is still widely used. The ratio of σabs/Bext (light absorption coefficient/atmospheric extinction coefficient) during the haze periods was higher than that of non-haze periods in spring, autumn and winter, proving higher BC concentration favored the decline in visibility. However, in all seasons, the decreasing ratio of σabs/Bext with the haze pollution getting worse, indicated that BC contributed less and other components (e.g., SO42−, NO3− and organics) contributed more to the visibility reduction when severe haze event occurred.

Exploring sources and health risks of metals in Beijing PM2.5: Insights from long-term online measurements

To gain a comprehensive understanding of sources, health risks, and regional transport of PM2.5-bound metals in Beijing, one-year continuous measurement (K, Fe, Ca, Zn, Pb, Mn, Ba, Cu, As, Se, Cr, and Ni) was conducted from December 2016 to November 2017 and Positive Matrix Factorization analysis (PMF) was applied for source apportionment. It was found that the seasonal variation of sources could vary significantly among metals. Sources of Ca, Ba, As, Se, and Cr did not show much seasonal variations, with the contribution of its predominant source higher than 35% in each season. However, the major sources of K, Fe, Zn, Pb, Mn, Cu, and Ni exhibited obvious seasonal variations. In addition, the characteristics of metals in haze episodes were comprehensively investigated. Haze episodes in Beijing were characterized by higher metal concentrations and health risks, which were about 2– 6 times higher than non-haze periods. Moreover, the types of haze episode were different in winter and spring. Haze episodes in winter were mostly influenced by coal combustion, the contribution of which increased greatly and accounted for about 30% of PM2.5. The metals such as K, Zn, Pb, As, and Se significantly increased, which were mainly transported from south of Beijing. During haze episodes in spring, dust was an important source, which contributed to higher concentrations of crustal metals that transported from northwest of Beijing. To quickly and effectively identify source regions of metals in Beijing during haze episodes, a new diagnostic ratio method using Ca as a reference was developed. The ratios of some anthropogenic metals to Ca significantly increased when air mass was mainly from south of Beijing during haze episodes while the ratios remained constantly low in non-haze periods, when local emissions dominated. This method could be useful for rapid identification and control of metal pollution in Beijing.

Nitrate aerosol formation and source assessment in winter at different regions in Northeast China

To fully identify the formation and source characteristics of aerosol nitrate during winter which accompanied by frequent haze in Northeast China, the nitrate concentrations, δ15N–NO3- and δ18O–NO3- characteristics of PM2.5 samples from four sites of different types including the (a) urban area, (b) suburban area, (c) suburban-rural transition area and (d) rural area in Northeast China were analyzed in this work. δ15N isotope fractionation (εN) during the conversion of atmospheric NOX (δ15N-NOX) to nitrate (δ15N–NO3-) was discussed on the basis of the estimated contributions of the gas phase oxidation pathway of OH radical (·OH) (γOH) and the heterogeneous hydrolysis pathway of N2O5 (γN2O5) to nitrate formation. Besides, the contribution of biological soil, coal combustion, biomass burning and motor vehicles to NOX emissions had also been analyzed using Bayesian isotope mixing model. Results showed that different types of sites had inconsistent source contributions. Obviously, coal combustion plays an absolutely indispensable role in the production of NOX in all the sites, especially in rural areas (d), where coal combustion contributed up to 89.8%. In addition, biomass burning still has a great effect on NOX emissions in the Northeast, showing a contribution of 5.2%–35.8%. It is worth noting that in urban site (a) where the tropospheric O3 concentration (34±9 μg m−3) was significantly lower than the other regions ((b): 54 ± 16 μg m−3, (c): 101 ± 21 μg m−3, (d): 98 ± 17 μg m−3), the contribution of the ·OH pathway to nitrate was as high as 69.4%, which was very different from the other three sites. The different formation mechanisms of nitrate in urban and non-urban may be due to different O3. Haze not only affects the sources of nitrate, but also changes the contribution of nitrate formation. Except for rural site (d), the contribution of the heterogeneous reaction (N2O5 pathway) of the other three sites during the haze period was greater (a: 35.1%, b: 60.0%, c: 59.0%, d: 60.8%) than in the non-haze period (a: 22.5%, b: 44.7%, c: 41.9%, d: 64.2%).

Investigating the effect of sources and meteorological conditions on wintertime haze formation in Northeast China: A case study in Harbin

Heavy haze pollution has occurred frequently in the past few years in Northeast China during winters, which was distinct from other regions in China because of the particular meteorological conditions. In this study, we analyzed the temporal variation, source appointment, and influencing factors of PM2.5 from December 1, 2018 to February 28, 2019 in Harbin. The results showed obvious differences between the non-haze and haze periods. The source appointment based on a single-particle aerosol mass spectrometer showed that coal combustion, vehicle emissions, biomass burning, and secondary inorganic aerosols (SIAs) were the major contributors of PM2.5. It is interesting that from the non-haze to the haze period, contributions of coal combustion and SIAs increased (from 20.2% to 27.3%, and from 17.3% to 18.9%, respectively) while other sources decreased or increased little. It indicated the primary pollutants from heating supply were the most important contributor to haze formation due to the low temperature. Furthermore, from levels I (0 < PM2.5 ≤ 75 μg m−3) to III (115 < PM2.5 ≤ 150 μg m−3), SIAs increased from 15.3% to 19.4% (increased 4.1%), while coal combustion from 23.7% to 27.1% and increased 3.4%. It implied clearly that SIAs played a comparable role in the early stage of the evolution of haze episode as that of coal combustion. Combining data on prevailing winds and results of potential source contribution function indicated that PM2.5 during the haze period was primarily influenced by the air masses originating from the southwestern areas via regional transport. A positive correlation was observed between relative humidity (RH) and haze pollution when RH ≥ 60%, indicating that hygroscopic growth may be the principal factor promoting secondary formation. CapsuleCoal combustion was the most important source in Harbin due to the low temperature, and secondary aerosols promoted the early stage of the haze evolution.

Measurement report: Comparison of wintertime individual particles at ground level and above the mixed layer in urban Beijing

Abstract. Beijing has been suffering from frequent severe air pollution events, with concentrations affected significantly by the mixed-layer height. Major efforts have been made to study the physico-chemical properties, compositions, and sources of aerosol particles at ground level. However, little is known about the morphology, elemental composition, and mixing state of aerosol particles above the mixed layer. In this work, we collected individual aerosol particles simultaneously at ground level (2 m above ground) and above the mixed layer in urban Beijing (within the Atmospheric Pollution and Human Health in a Chinese Megacity, APHH-Beijing, 2016 winter campaign). The particles were analyzed offline by transmission electron microscopy coupled with energy dispersive X-ray spectroscopy. Our results showed that the relative number contribution of mineral particles to all measured particles was much higher during non-haze periods (42.5 %) than haze periods (18.1 %); in contrast, internally mixed particles contributed more during haze periods (21.9 %) than non-haze periods (7.2 %) at ground level. In addition, more mineral particles were found at ground level than above the mixed-layer height. Around 20 % of individual particles showed core–shell structures during haze periods, whereas only a few core–shell particles were observed during non-haze periods (2 %). The results showed that the particles above the mixed layer were more aged, with a larger proportion of organic particles originating from coal combustion. Our results indicate that a large fraction of the airborne particles above the mixed layer come from surrounding areas influenced by coal combustion activities. This source contributes to the surface particle concentrations in Beijing when polluted air is mixed down to the ground level.

The Health Risks of Airborne Polycyclic Aromatic Hydrocarbons (PAHs): Upper North Thailand.

Every year, Northern Thailand faces haze pollution during the haze episode. The particulate matter (PM), including fine fraction (PM2.5), a coarse fraction (PM2.5–10), and 16 polycyclic aromatic hydrocarbons (PAHs), was measured in six provinces in upper north Thailand during the haze and non‐haze episodes in 2018. Eighty‐three percent of the PM2.5 measurements (21.8–194.0 µg/m3) during the haze episode exceeded the national ambient air quality standard in Thailand. All 16 PAHs were detected in the study area in both periods. The average concentration of total PAHs (particle‐bound and gas‐phase) during the haze episode was 134.7 ± 80.4 ng/m3, which was about 26 times higher than those in the non‐haze (5.1 ± 9.7 µg/m3). Naphthalene and acenaphthene were the dominant PAHs in the gas phase; whereas, indeno[123‐cd] pyrene, benzo[a]pyrene, and Benzo[ghi]Perylene were dominant in the particle‐bound phase. The estimated inhalation excess cancer risk from PAHs exposure was 9.3 × 10−4 and 2.5 × 10−5 in the haze episode and non‐haze, respectively. Diagnostic ratios and principal component analysis revealed that PAHs were derived from mixed sources of vehicle emission and solid combustion in the haze episode and vehicle emission in the non‐haze period. High pollution levels of PM and large cancer risk attributable to the exposure of PAHs in the haze episode suggest urgent countermeasures to reduce the source emission, especially from the solid combustion in the area.

Characteristics, emission sources and health risk assessment of trace elements in size-segregated aerosols during haze and non-haze periods at Ningbo, China.

To characterize trace elements from inhalable particles and to estimate human health risks, airborne particles at an urban area of Ningbo city during haze and non-haze periods from November 2013 to May 2014 were collected by a nine-stage sampler. Seventeen trace elements (Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd and Pb) were measured by inductively coupled plasma mass spectrometry (ICP-MS). The concentrations of trace elements are in the ranges of 0.51ngm-3 (Co) ~ 1.53µgm-3 (K) for fine particles (Dp < 2.1μm), and 1.07ngm-3 (Co) ~ 4.96µgm-3 (K) for coarse particles (2.1μm < Dp < 9.0μm) during the haze days, which are 1.15 -4.30 and 1.23- 7.83-fold as those of non-haze days, respectively. These elements could be divided into crustal elements (Na, Mg, Al, Ca, Ti, Fe and Co), non-crustal elements (Cu, Zn, Cd and Pb) and mixed elements (K, V, Cr, Mn, Ni and As) according to their enrichment factor values (EFs) and size distribution characteristics. Five emission sources of trace elements were identified by positive matrix factorization (PMF) modeling. The main sources of trace elements in fine particles are traffic emission (21.7%), coal combustion (23.6%) and biomass burning (32.1%); however, soil dust (61.5%), traffic emission (21.9%) and industry emissions (11.8%) are the main contributors for coarse particles. With the help of the multiple-path particle dosimetry (MPPD) model, it was found that deposition fractions of seventeen measured elements in the pulmonary region were in the range of 12.4%-15.1% and 6.66% -12.3% for the fine and coarse particles, respectively. The human health risk assessment (HRA) was employed according to the deposition concentration in the pulmonary region. The non-carcinogenic risk (HI) was below the safety limit (1.00). Nonetheless, the excess lifetime carcinogenic risk (ELCR) for adults increased by 2.42-fold during the haze days (2.06 × 10-5) as compared to that of non-haze days (8.50 × 10-6) in fine particles. Cr (VI) and As together contributed 96.5% and 96.3% of the integrated cancer risks during the haze and non-haze periods, respectively. Moreover, the related ELCR values in coarse particles were 36.7% and 62.8% of those in the fine particles for the non-haze period and haze period, respectively.

Characteristics of water-soluble inorganic aerosol pollution and its meteorological response in Wuhan, Central China

Due to the rapid economic development in Central China, PM2.5 (particles not larger than 2.5 μm) pollution is serious in recent years. To fully understand the causes of PM2.5 in this region, we conducted a long-term tracking (2015–2018) on water-soluble inorganic ions (WSIIs) in PM2.5, including sulfate (SO42−), nitrate (NO3−), ammonium (NH4+), chlorine (Cl−), potassium (K+), calcium (Ca2+), sodium (Na+), and magnesium (Mg2+). Results indicate that each ion has significant seasonal variations, with the maximum concentration in winter and minimum in summer. The secondary inorganic aerosols (SIAs) have remarkably higher concentrations in haze periods than non-haze periods, which indicates that the outbreak of haze is closely related to the massive generation of SIAs. Moreover, each ion shows a different response to the variation of meteorology, implying the different formation mechanisms. Generally, high pollution levels of Ca2+, Mg2+, K+, Cl−, and Na+ are correlated to prevailing winds, suggesting the significant contribution of regional transport. High concentrations of SIAs are usually accompanied by the low temperature (T < 15 °C), high relative humidity (RH > 60%), and calm wind, which means they are mainly locally generated. Under conditions with low T and high RH, more gaseous sulfur and nitrogen tend to be converted into solid inorganic salts, proved by the higher oxidation efficiency. Different to NO3−, SO42− is also easily generated at high T through photochemical oxidization. This study interprets fine particle pollution from the perspective of particle composition, and the results provide an reference for regional air pollution prevention.

Influence of Meteorological Conditions and Fire Hotspots on PM0.1 in Northern Thailand during Strong Haze Episodes and Carbonaceous Aerosol Characterization

ABSTRACT Northern Thailand has long been severely affected by haze from biomass burning containing fine and ultrafine aerosols in the dry period. The carbonaceous PM0.1 comprising elemental carbon (EC) and organic carbon (OC) collected during the haze and non-haze periods in Chiang Mai, Thailand was investigated. The PM0.1 levels during the haze periods were about 3 times higher than the non-haze periods, a significant increase. PM0.1 concentration was strongly correlated with atmospheric relative humidity and the number of forest fire hotspots. Carbonaceous aerosol characteristics in PM0.1 were analyzed with the thermal/optical transmittance (TOT) method following the IMPROVE protocol. The concentrations of OC and EC, distribution of OC and EC and OC/EC ratios in PM0.1 were evaluated. Average OC and EC mass concentrations in PM0.1 were 6.8 ± 2.7 and 1.4 ± 0.5 µg m–3 during the haze periods, significantly higher than those during the non-haze periods; 1.9 ± 0.9 and 0.5 ± 0.2 µg m–3. The OC/EC ratio increased linearly with the number of hotspots. This indicated significant contribution from biomass burning to the PM0.1. This was strongly supported by the 48-hr backward trajectory simulation, that indicated both domestic and transboundary aerosol transports. Because both organic and elemental carbon are the light-absorbing carbonaceous aerosols, the increase during the haze periods contributed to regional air quality and climate. This study enhances the understanding of PM0.1 behavior in Chiang Mai, Thailand, during the haze periods in upper southeast Asia.

Variation of carbonaceous aerosols and water soluble inorganic ions during winter haze in two consecutive years

The present study outlines the mechanism and brings out the chemistry involved in winter haze formation characterized by reduced visibility and severe respiratory problems especially in rural areas. It deals with the study of aerosol chemical composition and meteorological parameters in two consecutive winter seasons (2015/16 and 2016/17). Elevated PM2.5 mass concentrations were recorded (average = 231.5 ± 12.9 and 257.1 ± 21.9 μg m−3 in 2015/16 and 2016/17, respectively) during haze (polluted) days which was more than twice the PM concentrations during non-haze days (average = 101.6 ± 20.2 and 110.2 ± 25.4 μg m−3 in 2015/16 and 2016/17, respectively). During non-haze period, the contribution of carbonaceous aerosols (CAs) and secondary inorganic aerosols (SIAs) was 40% and 29% of PM2.5 but when haze formed both CAs and SIAs increased. During haze (polluted) episodes, high OC/EC ratios (>3.0) indicated secondary organic aerosol formation and high NH4+/SO42− molar ratios (>2.0) indicated the formation of (NH4)2SO4 and NH4HSO4 as major NH4+ salts. The results obtained with E-AIM Model simulations showed good agreement with measured values. E Aim Model IV was used to estimate liquid water content (LWC) and formation of inorganic salts. LWC (863 μg m−3; in situ hydrogen ion concentration, [H+]ins= 1.2 nmol m−3, and pH: 2.76) was high during haze (polluted) days as compared to non-haze days (750 μg m−3; [H+] ins= 2.4 nmol m−3, and pH:1.89) indicating enhanced hygroscopic growth of the ionic solids during haze (polluted) as compared to non-haze period. These results further corroborate the occurrence and predominance of heterogeneous reactions (under highly hygroscopic conditions) during haze (polluted) days in contrast to non-haze days when gas-phase as well as heterogeneous reactions both may occur.

Characterization of Metal Pollution of Regional Atmospheric PM2.5 and Its Sources Based on the PMF Model

As important components of PM2.5, metal elements are extremely harmful to people and also have source specificity. Understanding the characteristics of PM2.5 metal pollution in the two different types of cities can help adjust the layout of regional industrial structure and improve the environment. PM2.5 samples during haze/non-haze periods were collected in Chengdu City and Renshou County. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the mass concentrations of eighteen metal elements in collected PM2.5 samples. The positive matrix factorization (PMF) model was used for source apportionment analysis for metal elements in PM2.5. The analysis showed that the ratio of trace elements from fugitive dust, motor vehicle emissions, and coal burning to the total elements is greater in Chengdu City than that in Renshou County. The proportion of trace elements from biomass combustion, industrial, and fuel sources in Renshou County is higher than that in Chengdu City. In addition, concentrations of Cd, As, and Cr in both areas exceeded the standards, indicating the occurrences of heavy metal pollution. During the haze period, the total concentrations of compositional metal elements in PM2.5 increased, although the rate was much lower than that for PM2.5. The ratios of elements between haze and non-haze periods ranged from 0.7 (Al) to 2.8 (Ba) in Chengdu City, and from 0.8 (Al) to 3.1 (Mn) in Renshou County. Among all metal elements, the increase rate for trace elements from coal burning and industrial activities was relatively large but small for those from fugitive dust, with the growth in trace elements from motor vehicles being modest. The results of this study indicated that the characteristics of pollution and source of metal elements in PM2.5 varied by economic scale, development mode, and industrial layout. In large cities such as Chengdu City, where economic development is mainly focused on tertiary industry, air pollution is mainly caused by transportation and urban construction, while in suburban area such as Renshou County, where secondary or heavy industry are the focus for economic development, the pollution is mainly affected by energy consumption and industrial production.

A preliminary study on humic-like substances in particulate matter in Malaysia influenced by Indonesian peatland fires

In this paper, ambient total suspended particulates (TSP) with a focus on humic-like substances (HULIS) are characterized based on intensive ground-based field samplings collected in Malaysia during non-haze and haze periods caused by peatland fires on the Indonesian island of Sumatra. Furthermore, concentrations of water-soluble organic carbon (WSOC) and carbon content of HULIS (HULIS-C) were determined, and fluorescence spectra of the HULIS samples were recorded by excitation emission matrix (EEM) fluorescence spectroscopy. The concentrations of WSOC and HULIS-C over the entire period ranged from 4.1 to 24 and 1.3 to 18 μgC m−3, respectively. The concentrations of WSOC and HULIS-C during the peatland fire-induced strong haze periods were over 4.3 and 6.1 times higher, respectively, than the average values recorded during the non-haze periods. Even during the light haze periods, the concentrations of WSOC and HULIS-C were significantly higher than their averages during the non-haze periods. These results indicate that peatland fires induce high concentrations of WSOC, particularly HULIS-C, in ambient TSP at receptor sites. EEM fluorescence spectra identified fulvic-like fluorophores at the highest intensity level in the EEM fluorescence spectra of the haze samples. A peak at excitation/emission (Ex/Em) ≈ (290–330)/(375–425) nm is also observed at high intensity, though this peak is normally associated with marine humic-like fluorophores. It is shown that a peak at Ex/Em ≈ (290–330)/(375–425) nm is not derived from marine sources only; furthermore, peatland fires are shown to be important contributors to HULIS around this peak.

Speciated atmospheric mercury during haze and non-haze periods in winter at an urban site in Beijing, China: Pollution characteristics, sources, and causes analyses

Speciated atmospheric mercury (Hg) was measured at an urban site in Beijing, China from February to March 2018. The mean concentrations of gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM), and fine particulate bound mercury (PBM2.5) were 2.81 ± 0.90 ng m−3, 10.7 ± 8.5 pg m−3, and 60.6 ± 43.5 pg m−3, respectively. Reactive Hg (i.e., RM=GOM+PBM2.5) only represented ~2.4% of total atmospheric Hg. The GEM concentration at the monitoring site was 1.7 times higher than the average value in the Northern Hemisphere. In particular, the mean GEM and PBM2.5 concentrations were significantly higher during haze period (hourly average AQI value > 100 for at least consecutive 24 h) (3.65 ± 0.76 ng m−3 and 93.0 ± 37.1 pg m−3) than during non-haze period (2.42 ± 0.73 ng m−3 and 48.5 ± 39.5 pg m−3). One possible explanation is the strong subsidence of air masses during haze period could lead to the accumulation of air pollutants. However, there was no significant difference in GOM concentration between haze and non-haze periods. Although the ozone, relative humidity (RH), and planetary boundary layer (PBL) all followed a clear diurnal cycle, while for RM no distinct diurnal pattern was observed. Additionally, GEM was significantly positively correlated with CO, indicating that they had homogeneous sources; whereas, they were all negatively correlated with wind speed and PBL height. Based on the combination of potential source contribution function and clustering analyses, we found that high atmospheric Hg events during haze days were more likely caused by the domestic sources in the Circum-Bohai-Sea region, while the transboundary transport of the clean air masses originating from Siberia was attributed to the low GEM and PBM2.5 levels during non-haze days.