Thermo-optical properties of residential coals and combustion aerosols

The investigation of diesel soot emission using instrument combination of multi-wavelength photoacoustic spectroscopy and scanning mobility particle sizer

The parallel measurements of wavelength dependent optical absorption, particle number size distribution have made by a multi wavelength photoacoustic spectrometer (4λ-PAS) and scanning mobility particle sizer (SMPS) respectively at different modes of a diesel engine using two different types of fuel. The thermal evolution of the emission was also investigated using posterior temperature treatment of emission. The bimodal size distribution of emitted particles at a set reference temperature has been observed regardless of the applied fuel at idle. However, the emitted particulate assembly had lognormal size distribution falls into the accumulation mode at all other defined engine modes and both fuel types. The total number- and volume concentration (TNC and TVC) showed retrograde tendency with the increasing torque and rpm independently of the applied fuel types. The TNC values decreased up to 50% for both fuels with engine operation changes from idle engine mode(em#1) to low engine mode(em#2). With further increase in torque and rpm of engine, the change in TNC is negligible. On the other hand, the TVC remains more or less the same for idle to low engine mode transition and increased more than 60% for high mode (em#3) transition. The Optical Absorption Coefficient (OAC) values measured at the operational wavelengths of the 4λ-PAS instrument decreased at all wavelengths with increasing rpm and torque. The wavelength dependency quantified by Aerosol Ängström Exponent (AAE) was applied here for qualitative analysis of the carbonaceous emission and showed decreased values towards the higher engine speed and torque output of the engine. The proposed technique can be used as real-time, precise and accurate measurement of light absorption by DPM aerosols, which opens up novel possibilities for the volatility and thermal evolution investigation of diesel emissions.

Suitability of Different Methods for Measuring Black Carbon Emissions from Marine Engines

Black carbon (BC) emissions intensify global warming and are linked to adverse health effects. The International Maritime Organization (IMO) considers the impact of BC emissions from international shipping. A prerequisite for the anticipated limits to BC emissions from marine engines is a reliable measurement method. The three candidate methods (photoacoustic spectroscopy (PAS), laser-induced incandescence (LII), and filter smoke number (FSN)) selected by the IMO were evaluated with extensive ship exhaust matrices obtained by different fuels, engines, and emission control devices. A few instruments targeted for atmospheric measurements were included as well. The BC concentrations were close to each other with the smoke meters (AVL 415S and 415SE), PAS (AVL MSS), LII (Artium-300), MAAP 5012, aethalometers (Magee AE-33 and AE-42), and EC (TOA). In most cases, the standard deviation between instruments was in the range of 5–15% at BC concentrations below 30 mg Sm−3. Some differences in the BC concentrations measured with these instruments were potentially related to the ratio of light-absorbing compounds to sulphates or to particle sizes and morphologies. In addition, calibrations, sampling, and correction of thermophoretic loss of BC explained differences in the BC results. However, overall differences in the BC results obtained with three candidate methods selected by the IMO were low despite challenging exhaust compositions from marine diesel engines. Findings will inform decision making on BC emission control from marine engines.

Seasonal variations in the mass characteristics and optical properties of carbonaceous constituents of PM2.5 in six cities of North China

Carbonaceous constituents have various adverse impacts on human health, visibility, and climate change. Although comprehensive studies on the characteristics of carbonaceous constituents have been conducted recently, systematic studies covering both the mass characteristics and light-absorption properties of carbonaceous constituents on a regional scale in China are quite limited. In this study, current seasonal measurements of organic carbon (OC) and elemental carbon (EC) in PM_2.5 were investigated during autumn and winter (1-30 October 2017 and December 18, 2017 to January 17, 2018) in six selected cities located at the eastern foot of the Taihang Mountains: Beijing, Baoding, Shijiazhuang, Handan, Xinxiang, and Zhengzhou. Seasonal variations were similar when Beijing was excluded. The lowest concentrations of OC (18.33 ± 9.39 μg/m³) and EC (7.66 ± 5.64 μg/m³) were observed in Xinxiang (autumn) and Beijing (winter), respectively, while the highest concentrations of OC (38.43 ± 62.10 μg/m³) and EC (12.24 ± 24.67 μg/m³) occurred in Baoding during winter mainly due to elevated fuel combustion for space heating. The results of the potential source contribution function (PSCF) analysis suggested that border zones between several provinces in North China should be highlighted in order to strengthen pollution control. Moreover, by separating the optical properties of brown carbon from those of black carbon, we were able to estimate the contributions of brown carbon to the PM_2.5 total light-absorption coefficient. The results show that the brown carbon absorption coefficient (at 405 nm) in winter at six sites accounted for 21.2%, 33.3%, 34.7%, 39.1%, 48.6%, and 23.3% of the PM_2.5 light absorption, which are values that are comparable to the contribution of black carbon in Xinxiang. These results provide a more comprehensive understanding of carbonaceous constituents on a regional scale.

Black Carbon: The Concentration and Sources Study at the Nam Co Lake, the Tibetan Plateau from 2015 to 2016

We measured black carbon (BC) with a seven-wavelength aethalometer (AE-31) at the Nam Co Lake (NCL), the hinterland of the Tibetan Plateau (TP) from May 2015 to April 2016. The daily average concentration of BC was 145 ± 85 ng m−3, increasing by 50% since 2006. The seasonal variation of BC shows higher concentrations in spring and summer and lower concentrations in autumn and winter, dominated by the adjacent sources and meteorological conditions. The diurnal variation of BC showed that its concentrations peaked at 9:00–16:00 (UTC + 8), significantly related to local human activities (e.g., animal-manure burning and nearby traffic due to the tourism industry). The concentration-weighted trajectory (CWT) analysis showed that the long-distance transport of BC from South Asia could also be a potential contributor to BC at the NCL, as well as the biomass burning by the surrounding residents. The analyses of the absorption coefficient and absorption Ångström exponent show the consistency of sourcing the BC at the NCL. We suggest here that urgent measures should be taken to protect the atmospheric environment at the NCL, considering the fast-increasing concentrations of BC as an indicator of fuel combustion.

Optical properties investigation of the reactions between methylglyoxal and glycine/ammonium sulfate

In recent years, "brown carbon" (BrC), as an important contributor to light absorption and climate forcing as aerosols, has been one of the forefronts in the field of atmospheric research. Aqueous BrC aerosols can be formed through aqueous reactions of methylglyoxal (MG) with nitrogen compounds, such as glycine (Gly) and ammonium sulfate (AS). When exposed to nitrogen compounds for several days, aqueous carbonyl compound MG became absorbent and fluorescent in the ultraviolet and near visible regions, according to UV/Vis and fluorescence spectroscopies. Experiment results showed that optical absorption of two aqueous BrC solutions in the spectral range of 250-480 nm significantly increased with increasing reaction time. After the reactions of MG with Gly and AS, the product absorbance followed the order of MG-Gly>MG-AS. For H₂O₂ oxidation photolysis, the atmospheric aqueous BrC showed the dynamic nature. Reaction kinetic, effective quantum yields and size distribution studies were conducted in the paper. Fluorescence lifetime values of the two BrC solutions were calculated. LC/MS analysis results clearly indicated that complicated organic compounds were formed in the reactions of MG with Gly and AS.

Oxalate Formation Enhanced by Fe-Containing Particles and Environmental Implications

We used a single particle mass spectrometry to online detect chemical compositions of individual particles over four seasons in Guangzhou. Number fractions (Nfs) of all the measured particles that contained oxalate were 1.9%, 5.2%, 25.1%, and 15.5%, whereas the Nfs of Fe-containing particles that were internally mixed with oxalate were 8.7%, 23.1%, 45.2%, and 31.2% from spring to winter, respectively. The results provided the first direct field measurements for the enhanced formation of oxalate associated with Fe-containing particles. Other oxidized organic compounds including formate, acetate, methylglyoxal, glyoxylate, purivate, malonate, and succinate were also detected in the Fe-containing particles. It is likely that reactive oxidant species (ROS) via Fenton reactions enhanced the formation of these organic compounds and their oxidation product oxalate. Gas-particle partitioning of oxalic acid followed by coordination with Fe might also partly contribute to the enhanced oxalate. Aerosol water content likely played an important role in the enhanced oxalate formation when the relative humidity is >60%. Interactions with Fe drove the diurnal variation of oxalate in the Fe-containing particles. The study could provide a reference for model simulation to improve understanding on the formation and fate of oxalate, and the evolution and climate impacts of particulate Fe.

Humic-Like Substances (HULIS) in Aerosols of Central Tibetan Plateau (Nam Co, 4730 m asl): Abundance, Light Absorption Properties, and Sources

Humic-like substances (HULIS) are major components of light-absorbing brown carbon that play an important role in Earth's radiative balance. However, their concentration, optical properties, and sources are least understood over Tibetan Plateau (TP). In this study, the analysis of total suspended particulate (TSP) samples from central of TP (i.e., Nam Co) reveal that atmospheric HULIS are more abundant in summer than that in winter without obvious diurnal variations. The light absorption ability of HULIS in winter is 2-3 times higher than that in summer. In winter, HULIS are mainly derived from biomass burning emissions in South Asia by long-range transport. In contrast, the oxidation of anthropogenic and biogenic precursors from northeast part of India and southeast of TP are major sources of HULIS in summer.