• Energy Research

Atmospheric aerosol particles (also known as particulate matter) are central to the cause of the two greatest threats to human security: air pollution (~5 million premature deaths per year) and climate change (~0.5 million per year). Addressing these threats requires an understanding of particulate matter sources responsible for both extreme air pollution immediately affect- ing human health and less extreme levels affecting climate over longer timescales. Here, extraordinary levels of air pollution, with submicrometre aerosol (PM 1 ) mass concentration surpassing 300 µ g m -3 , were observed in a moderately sized European city and are attributed to emissions from residential solid fuel--specifically peat and wood, often promoted as 'slow-renew- able', 'low-carbon' or 'carbon-neutral' biomass. Using sophisticated fingerprinting techniques, we find that consumption of peat and wood in up to 12% and 1% of households, respectively, contributed up to 70% of PM 1 . The results from this approach can better inform emissions reduction policies and help to ensure the most appropriate air pollution sources are targeted. Given the far greater abundance of solid fuels and concomitant emissions required to match the calorific benefit of liquid fuels, even modest increases in the consumption of 'green'-marketed solid fuels will disproportionally increase the frequency of extreme pollution events.

Biomass burning is an important source of brown carbon (BrC) aerosols, which influence climate by affecting the Earth's radiative balance. However, the transformation pathways of BrC chromophores, especially in the presence of photochemically active species, such as nitrate, are not well understood. In this study, the nitrate-mediated aqueous-phase photooxidation of three typical BrC chromophores from biomass burning was investigated, including 4-nitrocatechol, 3-nitrosalicylic acid, and 3,4-dinitrophenol. Variations in nitrate concentrations, pH, and temperatures were systematically examined to assess their impacts on the apparent photolysis rates of these BrC chromophores. The results show that increasing nitrate concentrations significantly enhances apparent photolysis rates to 3-3.5 times compared to nitrate-free conditions. Also, a temperature rise from 0 to 30 °C increases apparent photolysis rates by a factor of 1.3-2.5 for these chromophores. However, the effect of pH varies among these chromophores, depending on the substituents and their positions on the benzene ring. High-resolution mass spectrometric analysis suggests that the photooxidation of these chromophores initiates with the addition of nitro and/or hydroxyl groups to the benzene ring, followed by a ring-opening reaction and the formation of smaller, highly oxygenated molecules including formic acid, glyoxylic acid, malonic acid, and nitropropanoic acid. This study highlights the key role of nitrate in the aqueous-phase photooxidation of BrC, altering the aging pathways and shortening the atmospheric lifetimes of BrC. These results are of particular importance for a better understanding of BrC aging and its radiative forcing, given the increase of the nitrate mass fraction in aerosols of China in recent years.

Brown carbon (BrC) from biomass burning constitutes a significant portion of light-absorbing components in the atmosphere. Although the aging of BrC surrogates from biomass burning has been studied in many laboratory settings, BrC aging behavior in real-world urban environments is not well understood. In this study, through a combination of online dynamic monitoring and offline molecular characterization, the ambient optical aging of BrC was linked to its dynamic changes in molecular composition. Enhanced light absorption by BrC was consistently observed during the periods dominated by oxygenated biomass burning organic aerosol (BBOA), in contrast to periods dominated by primary emissions or secondary formation in aqueous-phase. This enhancement was linked to the formation of nitrogen-containing compounds during the ambient aging of BBOA. Detailed molecular characterization, alongside analysis of environmental parameters, revealed that an increased atmospheric oxidizing capacity, marked by elevated levels of ozone and nighttime NO3 radicals, facilitated the formation of nitrated aromatic BrC chromophores. These chromophores were primarily responsible for the enhanced light absorption during the ambient aging of BBOA. This study elucidates the nitration processes that enhance BrC light absorption for ambient BBOA, and highlights the crucial role of meteorological conditions. Furthermore, our findings shed light on the chemical and optical aging processes of biomass burning BrC in ambient air, offering insights into its environmental behavior and effects.

Solid-fuel stoves are at the heart of many homes not only in developing nations, but also in developed regions where there is significant deployment of such heating appliances. They are often operated inefficiently and in association with high emission fuels like wood. This leads to disproportionate air pollution contributions. Despite the proliferation of these appliances, an understanding of particulate matter (PM) emissions from these sources remains relatively low. Emissions from five solid fuels are quantified using a "conventional" and an Ecodesign stove. PM measurements are obtained using both "hot filter" sampling of the raw flue gas, and sampling of cooled, diluted flue gas using an Aerosol Chemical Speciation Monitor and AE33 aethalometer. PM emissions factors (EF) derived from diluted flue gas incorporate light condensable organic compounds; hence they are generally higher than those obtained with "hot filter" sampling, which do not. Overall, the PM EFs ranged from 0.2 to 108.2 g GJ-1 for solid fuels. The PM EF determined for a solid fuel depends strongly on the measurement method employed and on user behavior, and less strongly on secondary air supply and stove type. Kerosene-based firelighters were found to make a disproportionately high contribution to PM emissions. Organic aerosol dominated PM composition for all fuels, constituting 50-65% of PM from bituminous and low-smoke ovoids, and 85-95% from torrefied olive stone (TOS) briquettes, sod peat, and wood logs. Torrefied biomass and low-smoke ovoids were found to yield the lowest PM emissions. Substituting these fuels for smoky coal, peat, and wood could reduce PM2.5 emissions by approximately 63%.

Source apportionment studies of particulate matter (PM) link chemical composition to emission sources, while health risk analyses link health outcomes and chemical composition. There are limited studies to link emission sources and health risks from ambient measurements. We show such an attempt for particulate trace elements. Elements in PM2.5 were measured in wintertime Beijing, and the total concentrations of 14 trace elements were 1.3-7.3 times higher during severe pollution days than during low pollution days. Fe, Zn, and Pb were the most abundant elements independent of the PM pollution levels. Chemical fractionation shows that Pb, Mn, Cd, As, Sr, Co, V, Cu, and Ni were present mainly in the bioavailable fraction. Positive matrix factorization was used to resolve the sources of particulate trace elements into dust, oil combustion, coal combustion, and traffic-related emissions. Traffic-related emission contributed 65% of total mass of the measured elements during low pollution days. However, coal combustion dominated (58%) during severe pollution days. By combining element-specific health risk analyses and source apportionment results, we conclude that traffic-related emission dominates the health risks by particulate trace elements during low pollution days, while coal combustion becomes equally or even more important during moderate and severe pollution days.

The health effects of trace metal elements in atmospheric fine particulate matter (PM2.5) are widely recognized, however, the emission factor profiles and chemical fractionation of metal elements in different sources were poorly understand. In this study, sixteen metal elements, including Cd, Pb, V, Zn, Ba, Sb, As, Fe, Sr, Cr, Rb, Co, Mn, Cu, Ni and Sn from biomass burning, bituminite and anthracite combustion, as well as dust, were quantified. The results show different emission sources were associated with distinct emission profiles, holding important implications for source apportionment of ambient particulate metals. Specifically, Fe was the dominant metal species (28-1922 mg/kg) for all samples, and was followed by different metals for different samples. For dust, Mn (39.9 mg/kgdust) had the second-highest emission factor, while for biomass burning, it was Cr and Ba (7.5 and 7.4 mg/kgbiomass, respectively). For bituminous coal combustion, the emission factor of Zn and Ba was 6.2 and 6.0 mg/kgbituminous, respectively, while for anthracite combustion the corresponding emission factor was 5.6 and 4.3 mg/kganthracite, respectively. Moreover, chemical fractionation (i.e., the exchangeable, reducible fraction, oxidizable, and residual fraction) and the bioavailability index (BI) values of the metal elements from different sources were further investigated to reveal the link between different emission sources and the potential health risk. The findings from this study hold important implications for source apportionment and source-specific particulate metal-associated health effects.

An aerosol chemical speciation monitor (ACSM) was deployed to study the primary nonrefractory submicron particulate matter emissions from the burning of commercially available solid fuels (peat, coal, and wood) typically used in European domestic fuel stoves. Organic mass spectra (MS) from burning wood, peat, and coal were characterized and intercompared for factor analysis against ambient data. The reference profiles characterized in this study were used to estimate the contribution of solid fuel sources, along with oil combustion, to ambient pollution in Galway, Ireland using the multilinear engine (ME-2). During periods influenced by marine air masses, local source contribution had dominant impact and nonsea-spray primary organic emissions comprised 88% of total organic aerosol mass, with peat burning found to be the greatest contributor (39%), followed by oil (21%), coal (17%), and wood (11%). In contrast, the resolved oxygenated organic aerosol (OOA) dominated the aerosol composition in continental air masses, with contributions of 50%, compared to 12% in marine air masses. The source apportionment results suggest that the use of domestic solid fuels (peat, wood, and coal) for home heating is the major source of evening and night-time particulate pollution events despite their small use.

Glyoxal (Gly) and methylglyoxal (Mgly) are key precursors globally for secondary organic aerosol (SOA) formation. These two species were often thought to be formed in the atmosphere via photochemical oxidation of organics from biogenic and anthropogenic origins, although few studies have shown their direct emissions. In this study, we report direct emissions of particulate Gly and Mgly from different residential fuels typically used in north China. The emission ratios (ERs) and emission factors (EFs) of particulate Gly and Mgly for biomass burning were approximate 5-fold and 7-fold higher than those for coal combustion, respectively. The large variances in emissions of Gly and Mgly could be attributed to the different combustion processes, which influenced by the fuel types and combustion conditions. The averaged ERs and EFs of particulate Gly and Mgly were about one order of magnitude lower than their gaseous counterparts due to the low Henry's law constant, which was also consistent with the low particle-to-gas ratio of Gly (0.04) and Mgly (0.02). Our results suggest that the direct emissions of Gly and Mgly from emission sources should be considered when estimating the formation of SOA from Gly and Mgly.