Contribution Of Biomass Burning Research Articles

Underestimated contribution of open biomass burning to terpenoid emissions revealed by a novel hourly dynamic inventory

Terpenoids play a crucial role in atmospheric chemistry, contributing significantly to the formation of ozone and secondary organic aerosol. However, the accurate quantification of terpenoid emissions from biomass burning is currently lacking, leading to underestimated air quality impacts. This study developed a near real-time hourly open biomass burning (OBB) emission inventory named OBEIC, which incorporated geostationary and polar-orbiting satellite fire radiative power. The OBEIC inventory provided emission estimates of 69 terpenoids, categorized into four groups, at an hourly resolution. Monoterpenes were the dominant contributors to the total emissions, accounting for 58 % of the total terpenoid emissions from OBB. Notably, only 24 % of the total monoterpenes emitted from OBB were accounted for by α-pinene and β-pinene, indicating the importance of quantifying emissions of other monoterpene species such as limonene and camphene. Additionally, oxygenated terpenoids, which were previously overlooked, contribute to 20 % of total terpenoid emissions from OBB. Diurnally, the emissions of terpenoids were primarily concentrated during the daytime (61 %); however, this study revealed the significance of nighttime emissions (39 %) as well. When compared to the biogenic and anthropogenic emissions, OBB made substantial contributions to nighttime isoprene (99.8 %), monoterpene (66.8 %), and sesquiterpene (61.7 %) emissions where OBB occurs (in 3 km range), suggesting its significant role in nighttime secondary pollutant formation. The methodology developed in this study has the potential to reduce uncertainties in OBB emissions estimation.

Understanding the seasonal dynamics of surface PM2.5 mass distribution and source contributions over Thailand

The escalating levels of aerosols have emerged as a significant concern for climate extremes in the Southeast Asian regions, particularly accentuated during El Nino Years. In this study, we utilized a combination of atmospheric measurements and modeling to investigate the seasonal and geographical distribution of PM2.5 mass concentrations and its primary contributors across Thailand during La Nina (2017) and El Nino (2019) years. Our findings revealed the highest daily mean surface PM2.5 mass concentration during the summer season across most regions, followed by winter, and the lowest levels during the rainy season. Notably, a significant shift in daily mean PM2.5 mass was observed from 2017 to 2019 across all seasons, with a pronounced increase of 70.9% over northern Thailand during the summer, attributed to heightened biomass burning (BB) contributions. In terms of source attribution for PM2.5 mass, the primary contributors in 2017 were BB at 34.3%, followed by anthropogenic emissions (AE) at 32.4%, and natural emissions (NE) at 30.1%. However, in 2019, the BB contribution surged to 47.4% nationwide. During El Nino years, BB played a significant role in shaping concentrations during summer and winter, while NE dominated the rainy season. An important implication of our findings is the significant potential for reducing daily and annual mean PM2.5 mass levels throughout Thailand by effectively reducing BB emissions.

Origins of formaldehyde in a mountainous background atmosphere of southern China

Formaldehyde (HCHO) is one of the key indicators of severe photochemical pollution and strong atmospheric oxidation capacity in southern China. However, current information on the origins of regional HCHO and the impacts of polluted air masses remains scarce and unclear. In this study, an intensive observation of HCHO was conducted at a mountainous background site in southern China during typical photochemical pollution episodes. The concentrations of HCHO reached up to 6.14 ppbv and averaged at 2.68 ± 1.11 ppbv. Source appointment using a photochemical age-based parameterization method revealed significant contributions of secondary formation (50 %) and biomass burning (42 %). Meanwhile, under the influence of the East Asian Winter Monsoon, polluted air masses from central and western China can significantly increase the regional HCHO levels. The simulation results adopting the Rapid Adaptive Optimization Model for Atmospheric Chemistry model further demonstrated that the intrusion of active anthropogenic pollutants (e.g., small-molecule alkenes) can accelerate the net production rate of HCHO, particularly through BVOC-oxidation pathways. This study suggests a potential enhanced mechanism of HCHO production resulting from anthropogenic-biogenic interactions. It highlights that polluted air masses carrying abundant HCHO from upwind areas may facilitate severe photochemical pollution in the Greater Bay Area.

Source apportionment of black carbon using an advanced Aethalometer model in a typical industrial city of China

Black carbon (BC) aerosol can lead to adverse health effects and drive climate change; therefore, the characteristic research and identification of BC sources are essential for lowering emissions. In this study, equivalent black carbon (eBC) measurement was performed using a seven-wavelength Aethalometer (AE33) at an urban site in a typical industrial city (Zibo) of Northern China for the first time. The monitoring was performed from February 2021 to January 2022. The mass absorption cross-section (MAC) of AE33 was optimised using the online elemental carbon (EC) data, and eBC was corrected using the MAC. The corrected annual BC concentration was 1.72 ± 1.18 µg/m3. The diurnal variation of BC depicted a bimodal distribution. Furthermore, the BC concentration on weekends was 18 % lower than on weekdays. The diurnal variation and weekend effect reflect the critical contributions of traffic emission to BC concentration. The source apportionment of BC was calculated by a constraining Aethalometer model, which restricted the Ångström exponent using the online potassium ions. The results revealed that BC was not significantly affected by biomass burning (BCbb) in Zibo. The relative contribution of BCbb was higher in winter than in other seasons. The daily morning peak of BC was primarily influenced by traffic sources, whereas the contribution of biomass burning increased after 17:00 in the evening peak. Our findings suggest that it is more important to control fossil fuel sources for BC emission reduction in Zibo, while it is necessary to strengthen the control of biomass combustion sources in winter.

Biomass Combustion in Boiler: Environmental Monitoring of Sugar Markers and Pollutants

The need to use renewable sources and matrices with energy potential is widely recognized. The development of innovative technologies aimed at the improvement of energy conversion processes and reducing environmental impacts is currently receiving increasing attention from the scientific community and policymakers. The presence of sugars in airborne particle materials is attributed to biomass combustion. For this reason, these compounds are considered markers of biomass burning. The purpose of this work was to evaluate the emissions produced by agroforestry biomass burning (citrus pruning) by simultaneously sampling both stack emissions and atmospheric particulates in the area around a biomass boiler to understand the real contribution of biomass burning to atmospheric pollution. The combustion tests were carried out by comparing the processes with and without particulate abatement system to see how biomass combustion’s contribution to particulate emission can be controlled and reduced. During the tests, the focus was on particulate matter (PM) speciation in terms of sugar marker identification and determination. This study aims to increase knowledge to better understand the contribution of biomass plants to air pollution and differentiate it from the contributions of other sources, such as vehicular traffic or domestic heating.

Organic tracers in fine and coarse aerosols at an urban Mediterranean site: contribution of biomass burning and biogenic emissions.

The concentrations of anhydrosugars (levoglucosan, mannosan, and galactosan), polyols (inositol, xylitol, sorbitol, and mannitol), and glucose were measured in PM1 and PM10 samples collected during 1 year at a traffic site in the city of Elche (southeastern Spain). Levoglucosan, mannosan, and galactosan were mainly found in the PM1 fraction since they are mainly emitted from biomass burning (BB). Likewise, inositol, xylitol, and sorbitol were primarily distributed in the fine mode, suggesting a non-negligible contribution from anthropogenic sources (specifically BB) to the levels of these compounds. This was supported by their seasonal variations, with higher concentrations during winter, and their correlations with levoglucosan concentrations. The average contributions of biomass burning and biogenic sources to OC and PM levels were calculated using levoglucosan and mannitol, respectively, as tracers. On average, BB accounted for 12% and 16% of the OC in PM1 and PM10, while the estimated contribution of fungal spores to OC and PM10 levels was 1.2 and 0.8%, respectively. The results of the present study suggest that, at least in the study area, most sugar alcohols are not appropriate tracers of biogenic emissions.

Characterization of Metal Elements in Atmospheric PM2.5 and Health Risk Assessment in Heze in Winter from 2017 to 2018

Atmospheric PM2.5 samples were collected in Heze, Shandong Province, from a total of three sampling sites at Heze College, Huarun Pharmacy, and a wastewater treatment plant between October 15, 2017 and January 31, 2018, to determine the concentrations of 21 metal elements in PM2.5 using inductively coupled plasma mass spectrometry (ICP-MS). The degree of elemental enrichment was also discussed, the health risks and potential heavy metal ecological risks were assessed. The results showed that ρ (PM2.5) ranged from 26.7 to 284.1 μg·m-3 at the three sampling sites during the sampling period, and the concentration values did not differ significantly, all of which were at high pollution levels. The highest concentrations of K were found in the three sampling sites, accounting for 31.03%, 39.47%, and 38.43% of the total, respectively, mainly due to the high contribution of biomass burning in autumn and winter in Heze, a large agricultural city. The highest concentrations of Zn, 89.70, 84.21, and 67.68 ng·m-3, were found in the trace elements at the three sampling sites, respectively. The enrichment factor results showed that the enrichment factor values of Zn, Pb, Sn, Sb, Cd, and Se were higher than 100, among which the enrichment factors of Cd and Se were higher than 2 000 and 4 000, respectively, which were significantly influenced by anthropogenic activities and might have been related to industrial production, metal smelting, road sources, and coal combustion emissions. The health risk results showed that there was some potential non-carcinogenic risk (HQ>0.1 for children and adults) for As and a combined potential non-carcinogenic risk (HI>0.1) and some potential carcinogenic risk (CRT>1×10-6) for both children and adults at the three sampling sites. There was a more significant carcinogenic risk (CRT>1×10-4) for adults at the wastewater treatment plant, and the slightly higher carcinogenic risk for adults than that for children may have been related to the longer outdoor activity and higher PM2.5 exposure for adults. The elements with the highest potential ecological risk values were Cd, As, and Pb, with Cd exhibiting a very high potential ecological risk that should be taken seriously. All three sampling sites showed a very high combined potential ecological risk, with the intensity spatially expressed as Heze College>Huarun Pharmacy>wastewater treatment plant.

Light absorption properties and source contributions of black and brown carbon in Guangxi, southern China

Black carbon (BC) and brown carbon aerosols (BrC) are primary light-absorbing carbonaceous aerosols that significantly influence the global and regional radiation balance, as well as air quality. Guangxi Zhuang Autonomous Region, as a primarily agricultural province of China and neighbouring Southeast Asia, is subjected to both local emissions and pollution transport from Southeast Asian biomass burning. To investigate the light absorption properties and source contributions of BC and BrC in this region, observations from a 7-wavelength Aethalometer are employed to estimate the light absorption properties of BC and BrC over the period from March to December 2020 in Nanning, China. This study focuses on analysing the absorption contributions of BC and BrC to the total absorption of carbonaceous aerosols, identifying their emission sources, and exploring the impact of long-range transport of biomass burning (BB) from Southeast Asia on BC and BrC based on backward trajectory and weighted concentration-weighted trajectories (WCWT) model. Our results show that the absorption Ångström exponent (AAE) of light-absorbing carbonaceous aerosols varies from 0.54 to 2.08, reflecting the presence of different absorbing aerosol sources with specific optical properties. The average absorption coefficients of BC and BrC at 370 nm, denoted as babs,BC(370) and babs,BrC(370), are 42.25 Mm−1 and 9.63 Mm−1, respectively, with the highest value observed in winter. The average absorption of BrC contributes 19% to the total absorption from light-absorbing carbonaceous aerosols, and this contribution decreases for high babs,BrC(370) values, with the highest value in summer at 20%. For the BC source apportionment using a site-specific AAE, fossil fuel combustion (FF) contributes 57%, with its highest proportion in summer (62%). Meanwhile, biomass burning (BB) accounts for 43%, with the greatest contribution in winter (58%). These results highlight the considerable role of BB in Guangxi. In terms of the BrC sources, secondary BrC (BrCsec) is responsible for 32% of the total light absorption of BrC at 370 nm, and is particularly characterized by a much higher level of 35% at night, meaning the dominant role of BrCsec in Nanning. The relative contribution of babs,BrC,sec(370) increases with a higher contribution of babs,BrC(370) to aerosol absorption. Compared with the BrCsec, primary BrC values are higher in spring and winter, due to the increased emissions from biomass burning. Based on the analysis of backward trajectory and WCWT, the increase in BC and BrC during March and April is mainly influenced by the long-range transport of BB from Southeast Asian countries, e.g., Laos and Thailand. Overall, the contributions of BB and FF emissions to BC are comparable in Guangxi, while BrC mainly formed from primary sources is significantly impacted by both local emissions and the long-range transport of BB. Studying the optical characteristics and emission sources in this region can promote the understanding of the radiative effect of light-absorbing carbonaceous aerosols under the joint contributions from biomass burning and industrial emissions.

Aerosol source apportionment uncertainty linked to the choice of input chemical components

For a Positive Matrix Factorization (PMF) aerosol source apportionment (SA) studies there is no standard procedure to select the most appropriate chemical components to be included in the input dataset for a given site typology, nor specific recommendations in this direction. However, these choices are crucial for the final SA outputs not only in terms of number of sources identified but also, and consequently, in the source contributions estimates. In fact, PMF tends to reproduce most of PM mass measured independently and introduced as a total variable in the input data, regardless of the percentage of PM mass which has been chemically characterized, so that the lack of some specific source tracers (e.g. levoglucosan) can potentially affect the results of the whole source apportionment study. The present study elaborates further on the same concept, evaluating quantitatively the impact of lacking specific sources’ tracers on the whole source apportionment, both in terms of identified sources and source contributions. This work aims to provide first recommendations on the most suitable and critical components to be included in PMF analyses in order to reduce PMF output uncertainty as much as possible, and better represent the most commons PM sources observed in many sites in Western countries. To this aim, we performed three sensitivity analyses on three different datasets across EU, including extended sets of organic tracers, in order to cover different types of urban conditions (Mediterranean, Continental, and Alpine), source types, and PM fractions. Our findings reveal that the vehicle exhaust source resulted to be less sensitive to the choice of analytes, although source contributions estimates can deviate significantly up to 44 %. On the other hand, for the detection of the non-exhaust one is clearly necessary to analyze specific inorganic elements. The choice of not analysing non-polar organics likely causes the loss of separation of exhaust and non-exhaust factors, thus obtaining a unique road traffic source, which provokes a significant bias of total contribution. Levoglucosan was, in most cases, crucial to identify biomass burning contributions in Milan and in Barcelona, in spite of the presence of PAHs in Barcelona, while for the case of Grenoble, even discarding levoglucosan, the presence of PAHs allowed identifying the BB factor. Modifying the rest of analytes provoke a systematic underestimation of biomass burning source contributions. SIA factors resulted to be generally overestimated with respect to the base case analysis, also in the case that ions were not included in the PMF analysis. Trace elements were crucial to identify shipping emissions (V and Ni) and industrial sources (Pb, Ni, Br, Zn, Mn, Cd and As). When changing the rest of input variables, the uncertainty was narrow for shipping but large for industrial processes. Major and trace elements were also crucial to identify the mineral/soil factor at all cities. Biogenic SOA and Anthropogenic SOA factors were sensitive to the presence of their molecular tracers, since the availability of OC alone is unable to separate a SOA factor. Arabitol and sorbitol were crucial to detecting fungal spores while odd number of higher alkanes (C27 to C31) for plant debris.

Source identification and health risk assessment of particle phase organic compounds in urban and rural areas of Bangladesh

Particle phase organic compounds (PPOCs) constitute a significant portion of suspended organic compounds in the atmosphere, impacting human health. Limited research on sources, seasonal variations, and health effects in Bangladesh motivated this study, where particulate matter samples were collected in Dhaka, Rajshahi, Narayangonj, and Bhola from January 2015 to February 2019. Sixteen PPOCs concentrations were measured using a Gas Chromatography-Mass Spectrometry (GC-MS). Average PPOC concentrations were 11.60 ± 0.1 µgm-3 in Dhaka, 8.69 ± 0.3 µgm-3 in Rajshahi, 11.84 ± 0.4 µgm-3 in Narayangonj, and 7.22 ± 0.2 µgm-3 in Bhola, with 2 to 18 times higher concentrations in winter than monsoon season. Positive Matrix Factorization (PMF) identified major PPOCs sources as diesel exhaust, biomass burning, industrial emissions, and gasoline exhaust. Urban areas were dominated by industrial emissions, while rural regions had significant biomass burning contribution. Health risk assessment indicated a hazard index (HI) of 30.2, signifying severe non-carcinogenic effects, with Dimethoate contributing significantly (32%). The average lifetime cancer risk (2.94 × 10-3) exceeded USEPA guidelines, suggesting heightened cancer risk. Naphthalene posed the highest carcinogenic risk. Given anthropogenic sources and severe health impacts, public awareness and localized research are crucial.

Tropical tropospheric ozone and carbon monoxide distributions: characteristics, origins, and control factors, as seen by IAGOS and IASI

Abstract. The characteristics and seasonal variability in the tropical tropospheric distributions of ozone (O3) and carbon monoxide (CO) were analysed based on in situ measurements provided by the In-service Aircraft for a Global Observing System (IAGOS) programme since 1994 and 2002, respectively, combined with observations from the Infrared Atmospheric Sounding (IASI) instrument on board the MetOp-A satellite since 2008. The SOFT-IO (SOft attribution using FlexparT and carbon monoxide emission inventories for In-situ Observation database) model, which couples back trajectories with CO emission inventories, was used to explore the origins and sources of the tropical CO observed by IAGOS. The highest O3 and CO mixing ratios occur over western Africa in the lower troposphere (LT: surface to 750 hPa) during the fire season (75 ppb of O3 at 2.5 km and 850 ppb of CO at 0.3 km over Lagos in January), mainly due to anthropogenic (AN) emissions and a major contribution from fires. The secondary maxima are observed in Asia in the mid-troposphere (MT: 750–300 hPa) and upper troposphere (UT: 300–200 hPa) in April for O3 and in the LT in January for CO, with larger contributions from AN emissions. The lowest O3 and CO mixing ratios occur over Caracas. In the tropical LT, the majority of the location clusters are affected by local and regional AN emissions. The highest AN impact is found over Asia, Arabia and eastern Africa, and South America (>75 % of CO). Biomass burning (BB) emissions also originate from local or regional sources but with stronger seasonal dependence. The highest BB impact is found over southern tropical Africa (57 %–90 %), except in April, mostly due to local fires, but also from Northern Hemisphere Africa in January (45 %–73 %) and Southern Hemisphere South America in October (29 % over Windhoek). In the MT and UT, AN emissions are more important and dominate in the eastern part of the tropics (from the Middle East to Asia). BB contributions are more important than in the LT, especially from the African fires in January and July and from South East and equatorial Asia in April and October. The overall highest amount of CO is exported from Africa, with the main transport pathway from the dry-season African regions towards the wet-season ones. In contrast, the impact of the Asian emissions in the LT and MT is limited on a local or regional scale. The transport of polluted Asian air masses is important in the UT during the Asian summer monsoon and post-monsoon seasons, when convection is active.

Insights the dominant contribution of biomass burning to methanol-soluble PM2.5 bounded oxidation potential based on multilayer perceptron neural network analysis in Xi'an, China

Atmospheric fine particulate matter (PM2.5) is associated with cardiorespiratory morbidity and mortality due to its ability to generate reactive oxygen species (ROS). Ambient PM2.5 samples were collected during heating and nonheating seasons in Xi'an, China, and the ROS-generation potential of PM2.5 was quantified using the dithiothreitol (DTT) assay. Additionally, positive matrix factorization combined with multilayer perceptron was employed to apportion sources contributing to the oxidation potential of PM2.5. Both the mass concentration of PM2.5 and the volume-based DTT activity (DTTv) were higher during the heating season than during the nonheating season. The primary contributors to DTTv were combustion (biomass and coal) sources during the heating season (>52 %), whereas secondary formation dominated DTT activity during the nonheating season (35.7 %). In addition, the secondary reaction process promoted the generation of intrinsic oxidation potential (OP) of sources. Among all the sources investigated (traffic source, industrial emission, mineral dust, biomass burning, secondary formation and coal combustion), the inherent oxidation potential of biomass burning was the highest, whereas that of mineral dust was the lowest. Our study indicates that anthropogenic sources, especially biomass burning, should be prioritized in PM2.5 toxicity control strategies.

Contributions of biomass burning in 2019 and 2020 to Arctic black carbon and its transport pathways

The circum-Arctic region experienced serious fires in 2019 and 2020. Biomass burning is considered a primary source of black carbon (BC) aerosols. BC contributes to Arctic warming and impacts snow/ice melting. However, the impacts of biomass burning on BC in the Arctic during these recent serious fires have not been quantified in detail. In this study, based on numerical simulations using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), we calculated the contribution ratios of biomass burning to Arctic BC and revealed its transport pathways. Affected by biomass burning emissions, the near-surface BC concentrations over the terrestrial areas within the Arctic Circle were highest in summer, and declined in spring and autumn. Spatially, high-concentration levels of BC were distributed in the Russian central and eastern areas. Biomass burning accounted for 63.72% and 45.18% of the summer BC in the Arctic near-surface and middle troposphere, respectively. In the near-surface, the contributions from local Arctic sources were comparable to those from sources outside the Arctic Circle in summer. In the middle troposphere, contributions from sources outside the Arctic Circle were dominant. In summer, BC originating from biomass burning in Siberia was transported a short distance by southwesterly winds to the central Arctic near-surface, while the enhanced southwesterly winds in the middle troposphere transported BC from Siberia, Alaska and northern Canada to the central Arctic and Greenland. In spring and autumn, most BC originating from biomass burning in the near-surface of Eurasia was transported eastward by westerly winds and then transported northward over the North Pacific Ocean, and the long distance may have resulted in fewer effects on the Arctic. These results highlight the important role of biomass burning in the Arctic environment under a warming climate.

Quantifying the Nitrogen Sources and Secondary Formation of Ambient HONO with a Stable Isotopic Method.

Nitrous acid (HONO) is a reactive gas that plays an important role in atmospheric chemistry. However, accurately quantifying its direct emissions and secondary formation in the atmosphere as well as attributing it to specific nitrogen sources remains a significant challenge. In this study, we developed a novel method using stable nitrogen and oxygen isotopes (δ15N; δ18O) for apportioning ambient HONO in an urban area in North China. The results show that secondary formation was the dominant HONO formation processes during both day and night, with the NO2 heterogeneous reaction contributing 59.0 ± 14.6% in daytime and 64.4 ± 10.8% at nighttime. A Bayesian simulation demonstrated that the average contributions of coal combustion, biomass burning, vehicle exhaust, and soil emissions to HONO were 22.2 ± 13.1, 26.0 ± 5.7, 28.6 ± 6.7, and 23.2 ± 8.1%, respectively. We propose that the isotopic method presents a promising approach for identifying nitrogen sources and the secondary formation of HONO, which could contribute to mitigating HONO and its adverse effects on air quality.

Characterization of summertime single aerosol particles in Chengdu (China): Interannual evolution and impact of COVID-19 lockdown

To investigate the interannual evolution of air pollution in summer and the impact of the COVID-19 lockdown on local pollution in Chengdu, China, single aerosol particles were continuously measured in three summer periods: the regular period in 2020 (RP2020); the regular period in 2022 (RP2022); and the lockdown period in 2022 (LP2022). It was found that, from RP2020 to RP2022, the mass concentrations of PM2.5, PM10, SO2 and NO2 decreased by 25.6 %, 24.7 %, 28.8 % and 38.5 %, respectively, while the concentration of O3 increased by 11.0 %. Affected by regional transport, there was no significant decrease in the concentrations of various pollutants during LP2022. All single aerosol particles could be classified into seven categories: vehicle emissions (VE), dust, biomass burning (BB), coal combustion (CC), K mixed with sulfate (KSO4), K mixed with nitrate (KNO3) and K mixed with sulfate and nitrate (KSN) particles. From RP2020 to RP2022, the contributions of BB and CC particles decreased by 12.1 % and 0.9 %, respectively, while VE and dust particles increased by 3.6 % and 2.5 %, respectively; and compared to RP2022, the contributions of VE, dust and CC particles in LP2022 decreased by 22.2 %, 11.0 % and 12.7 %, respectively. The high PM2.5 pollution events in RP2020 and RP2022 were mainly caused by combustion sources (BB and CC, 51.6 %) and VE (38.3 %) particles, respectively, while the pollution event in LP2022 was contributed by BB (27.0 %) and secondary inorganic (KSO4, KNO3 and KSN, 60.2 %) particles. The formation mechanisms of different pollution events were further validated by WRF-Chem results. Although the potential source areas of particles showed a shrinking trend from RP2020 to RP2022, regional transport still caused high PM2.5 pollution events during LP2022. Photochemical processes dominated the formation of KSO4 particles, while the KNO3 and KSN particles were mainly generated by liquid-phase reactions, and this effect increased year by year.

Exploration of the downward transport mechanisms of biomass burning emissions from Indochina at the low boundary layer in East Asia

Springtime is the biomass burning (BB) season in Indochina. BB emissions are transported to East Asia and Taiwan at elevations of between 2000 and 4000 m and then transported downward to the near-surface layer when weather conditions are favorable. In this study, a numerical model, the Weather Research Forecast with Chemistry (WRF–Chem) model with tracer simulation was employed to explore the downward transport mechanisms and evaluate their potential effects on the planetary boundary layer (PBL) and near-surface layer during the springtime (Feb.–April) in 2018. Ambient backscatter was measured through LiDAR, aerosol optical depth was measured by MODIS and Himawari-8 satellites and by ground observations from the stations of AERONET. The data were applied to identify the transport mechanisms and evaluate the performance of the model. We summarized the downward transport mechanisms surrounding Taiwan, including the thermal effects of mountain downslope circulations (MDC), frontal secondary circulation (FSC) downward transport, and the mixing of MDC and FSC (MMF). Over Taiwan, the contributions of BB emissions for the MDC to the near-surface layer (<500 m), PBL (<1500 m), and free atmosphere (1500–6000 m) were 0.4%, 4.7%, and >95%, respectively, during springtime in 2018. For the FSC (MMF) mechanisms, the BB contributions to the near-surface layer, PBL, and free atmosphere were 2.5% (3.3%), 15.7% (17.1%), and 84.3% (82.9%), respectively. MMF occurred the most frequently among these three mechanisms and had the largest effect on the near-surface layer and PBL. The downward contributions of BB in different regions, including Taiwan, southern China, and the East China Sea (ECS), were also evaluated. Southern China had the highest value (11.0% [2.1%]) in the PBL (near-surface layer), followed by Taiwan and the ECS (8.2% [1.2%] and 4.5% [0.4%]). Overall, this research fills a gap in our understanding of the mechanisms by which BB emissions are transported to the surface and how they affect air quality in East Asia in general and Taiwan in particular.

Increased contribution of biomass burning to haze events in Shanghai since China’s clean air actions

High levels of East Asian black carbon (BC) aerosols affect ecological and environmental sustainability and contribute to climate warming. Nevertheless, the BC sources in China, after implementing clean air actions from 2013‒2017, are currently elusive due to a lack of observational constraints. Here we combine dual-isotope-constrained observations and chemical-transport modelling to quantify BC’s sources and geographical origins in Shanghai. Modelled BC concentrations capture the overall source trend from continental China and the outflow to the Pacific. Fossil sources dominate (~70%) BC in relatively clean summer. However, a striking increase in biomass burning (15‒30% higher in a fraction of biomass burning compared to summer and 2013/2014 winter), primarily attributable to residential emissions, largely contributes to wintertime BC (~45%) pollution. It highlights the increasing importance of residential biomass burning in the recent winter haze associated with >65% emissions from China’s central-east corridor. Our results suggest clearing the haze problem in China’s megacities and mitigating climate impact requires substantial reductions in regional residential emissions, besides reducing urban traffic and industry emissions.

Characteristics of atmospheric black carbon and its wet scavenging in Nanning, South China

Based on in-situ measurement of black carbon (BC) and carbon monoxide (CO), the characteristics of BC emissions and wet scavenging were comprehensively investigated in Nanning, South China. The average annual BC concentration was 1.02 ± 0.53 μg m−3 with higher pollution levels during winter. In winter, a higher net BC/CO (ΔBC/ΔCO) ratio of 3.3 ± 0.3 ng m−3 ppb−1 along with an increased absorption Ångström exponent (AAE) and BC mass from biomass burning (BCbb), indicated a significant contribution of biomass burning to BC emissions. However, emissions from the traffic sector consistently exerted a dominant influence throughout the year. Cluster analysis of backward trajectories identified three types of air masses with distinct origins. Cluster #1 originated from Guangxi province and its vicinity, intermittently influencing the sampling site throughout the year with varying effects between winter and summer. This air mass brought in clean sea breeze in summer whereas transported a higher proportion of BCbb to the site during wintertime due to local open biomass burning. Cluster #3 primarily arrived in autumn and winter (October–December) from polluted central China, resulting in substantially high BC mass at the site. Cluster #2 coincided with the period (January–March) when extensive surface open biomass burning events occurred in Southeast Asia (SEA) regions. These BC aerosols in cluster#2 initially rose to higher altitudes above SEA before being regionally transported, but were significantly scavenged by clouds and precipitation during vertical uplift. The remaining BC exhibited a notably lower BC loss rate on relative humidity (RH) of −0.01 ng m−3 ppb−1 %−1 compared to cluster #1 (−0.03) and cluster #3 (−0.06), corresponding to an average BC transport efficiency of 0.85, 0.73, and 0.53, respectively. Nonetheless, air masses in cluster #2 could still transport considerably high BC mass to Nanning due to dry conditions and less wet scavenging along trajectory pathways. These findings provide valuable insights for policymakers and government officials in regulating and mitigating BC pollution in South China.

The important contribution of secondary formation and biomass burning to oxidized organic nitrogen (OON) in a polluted urban area: insights from in situ measurements of a chemical ionization mass spectrometer (CIMS)

Abstract. To investigate the sources and formation mechanism of oxidized organic nitrogen (OON), field measurements of OON were conducted using an iodide-adduct chemical ionization mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-CIMS) during fall of 2018 in the megacity of Guangzhou, China. Using levoglucosan as a tracer of biomass burning emissions, the results show that biomass burning (49±23 %) and secondary formation (51±23 %) accounted for comparable fractions to the total particle-phase OON (pOON) but 24±25 % and 76±25 % to the gas-phase OON (gOON), respectively, signifying the important contribution of biomass burning to pOON and secondary formation to gOON in this urban area. Calculations of production rates of gOON indicated that hydroxyl radical (42 %) and nitrate radical (NO3) (49 %) oxidation pathways potentially dominated the secondary formation of gOON. A high concentration of NO3 radicals during the afternoon was observed, demonstrating that the daytime NO3 oxidation might be more important than the previous recognition. Monoterpenes, found to be major precursors of secondary gOON, were mainly from anthropogenic emissions in this urban area. The ratio of secondary pOON to Ox ([Ox] = [O3] + [NO2]) increased as a function of relative humidity and aerosol surface area, indicating that heterogeneous reaction might be an important formation pathway for secondary pOON. Finally, the highly oxidized gOON and pOON with 6 to 11 oxygen atoms were observed, highlighting the complex secondary reaction processes of OON in the ambient air. Overall, our results improve the understanding of the sources and dynamic variation of OON in the urban atmosphere.

Source apportionment of PM2.5 oxidative potential in an East Mediterranean site

This study aimed to evaluate the oxidative potential (OP) of PM2.5 collected for almost a year in an urban area of the East Mediterranean. Two acellular assays, based on ascorbic acid (AA) and dithiothreitol (DTT) depletion, were used to measure the OP. The results showed that the mean volume normalized OP-AAv value was 0.64 ± 0.29 nmol·min−1·m−3 and the mean OP-DTTv was 0.49 ± 0.26 nmol·min−1·m−3. Several approaches were adopted in this work to study the relationship between the species in PM2.5 (carbonaceous matter, water-soluble ions, major and trace elements, and organic compounds) or their sources and OP values. Spearman correlations revealed strong correlations of OP-AAv with carbonaceous subfractions as well as organic compounds while OP-DTTv seemed to be more correlated with elements emitted from different anthropogenic activities. Furthermore, a multiple linear regression method was used to estimate the contribution of PM2.5 sources, determined by a source-receptor model (Positive Matrix Factorization), to the OP values. The results showed that the sources that highly contribute to the PM2.5 mass (crustal dust and ammonium sulfate) were not the major sources contributing to the values of OP. Instead, 69 % of OP-AAv and 62 % of OP-DTTv values were explained by three local anthropogenic sources: Heavy Fuel Oil (HFO) combustion from a power plant, biomass burning, and road traffic emissions. As for the seasonal variations, higher OP-AAv values were observed during winter compared to summer, while OP-DTTv did not show any significant differences between the two seasons. The contribution of biomass burning during winter was 33 and 34 times higher compared to summer for OP-AAv and OP-DTTv, respectively. On the other hand, higher contributions were observed for HFO combustion during summer.