Organic Carbon Aerosols Research Articles

Spectral absorption properties of organic carbon aerosol during a polluted winter in Beijing, China

A fraction of organic carbon (OC) is found to exhibit the capability to absorb solar radiation. However, the absorption properties of OC remain poorly characterized partly due to uncertainties in determination methods. In this study, the absorption coefficient (bap) of OC (bap,OC) in Beijing during a polluted winter was estimated on the basis of the combined measurements of black carbon (BC) size distribution and total aerosol bap (bap,meas). The bare BC bap (bap,bareBC) calculated using Mie theory on the basis of measured size distribution exhibited weak wavelength dependence, with a mean absorption Ångström exponent (AAE) of 0.56 ± 0.04 within the 470–660 nm wavelength range, which was lower than the value of 1 commonly used for freshly emitted BC. The calculated bap,bareBC was compared with bap,meas at 950 nm to derive the coating thickness of BC, from which the calculation of coated BC bap (bap,coatBC) within 370–660 nm was based using the core–shell Mie model. Given the thick coatings, the AAE of coated BC, with a mean of 0.53 ± 0.12, was slightly lower than that of bare BC. Subsequently, bap,OC was obtained by subtracting bap,coatBC from bap,meas, accounting for 59.57 ± 4.82% of bap,meas at 370 nm on average. The average mass absorption efficiency of OC was estimated to be 1.48 ± 0.36 m2 g−1 at 370 nm. bap,OC significantly decreased as wavelength increased, deriving an AAE of OC with a mean of 2.72 ± 0.32 within the 370–660 nm range. The level of bap,OC estimated on the basis of a widely used attribution method assuming a constant BC AAE of 1 was ~60% lower than the currently presented value, probably underestimating OC radiative effect by a factor of >3. More accurate estimations of bap,OC based on more advanced measurements and suitable theory calculations are recommended to provide more reliable assessments of OC radiative effects.

Light absorption properties and potential sources of brown carbon in Fenwei Plain during winter 2018–2019

A distinctive kind of organic carbon aerosol that could absorb ultraviolet-visible radiation is called brown carbon (BrC), which has an important positive influence on radiative budget and climate change. In this work, we reported the absorption properties and potential source of BrC based on a seven-wavelength aethalometer in the winter of 2018–2019 at an urban site of Sanmenxia in Fenwei Plain in central China. Specifically, the mean value of BrC absorption coefficient was 59.6 ± 36.0 Mm−1 at 370 nm and contributed 37.7% to total absorption, which made a significant impact on visibility and regional environment. Absorption coefficients of BrC showed double-peak pattern, and BrC had shown small fluctuations under haze days compared with clean days. As for the sources of BrC, BrC absorption coefficients expressed strong correlations with element carbon aerosols and primary organic carbon aerosols, indicating that most of BrC originated from primary emissions. The linear correlations between trace metal elements (K, As, Fe, Mn, Zn, and Pb) and BrC absorption coefficients further referred that the major sources of BrC were primary emissions, like coal burning, biomass burning, and vehicle emissions. The moderate relationship between BrC absorption coefficients and secondary organic aerosols suggested that secondary production of BrC also played an important role. The 120 hr backward air mass trajectories analysis and concentration-weighted trajectories analysis were also used to investigate potential sources of BrC in and around this area, which inferred most parts of BrC were derived from local emissions.

Temporal and spatial variability of carbonaceous species (EC; OC; WSOC and SOA) in PM2.5 aerosol over five sites of Indo-Gangetic Plain

A year-long offline based study was performed at five sites of Indo-Gangetic plain to get the spatio-temporal variation in elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC) and secondary organic aerosol (SOA) in PM2.5 fraction. OC constitutes ~70–90% of the total carbon with high water-soluble fraction (60–70%) during winter, except at Hisar. The change in concentration of OC was insignificant during summer, whereas the water-soluble fraction increased by 75–85%. The relatively high OC/EC ratio (7–11) and OC/K+ ratio (10–52) during winter and post-monsoon suggest the dominance of biomass burning from wood fuel and agricultural waste. EC is nearly constant over the seasons at all sites suggesting the dominant presence of traffic-originated EC throughout the year. Interestingly, a low correlation (~0.3) between OC and EC at IITD and IITMD indicates their source from different origins. Exceptionally, the daytime OC/EC ratio was slightly higher than night time during winter at Hisar. However, other sites showed the opposite trend. A significant linear relationship between WSOC and secondary organic carbon suggests dominant contribution from SOA. A paired t-test results indicate much of WSOC is of secondary origin and regional in nature. The secondary fraction contributed 30–60% of OC during winter across all the sites in IGP, whereas during summer it varied between 20 and 40%. SOA estimated by the EC- tracer method has the highest contribution at IITMD (~138 μg/m3) among all the sites and peaked during post-monsoon.

Investigating the all-sky surface solar radiation and its influencing factors in the Yangtze River Basin in recent four decades

This study uses the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) reanalysis product to analyze the all-sky surface solar radiation (SSR) over the Yangtze River basin (YRB) and the quantitative impact of main factors from 1980 to 2018. Radiation data and multiple atmospheric factors were inputted into a multiple linear regression model. The regression results showed that aerosols and total clouds were the dominant factors affecting annual SSR variation. The aerosol radiative effect (ARE) and cloud radiative effect (CRE) were then calculated to quantify the effects of aerosols and clouds on SSR based on the MERRA-2 dataset. The average ARE and CRE in the YRB was −10.70 ± 2.01 and −47.92 ± 2.31 W/m2, respectively, which means that clouds attenuate SSR more than aerosols. SSR showed a general decline throughout the region (−0.156 W/m2 per year) and decreased significantly in the Sichuan Basin (SB, −0.242 W/m2 per year). The enhanced weakening of the radiative cooling effect of aerosols and clouds determines the decrease in the SSR. In Central China (CC), ARE had significantly enhanced (−0.297 W/m2 per year) and CRE had significantly weakened (0.207 W/m2 per year). From 1980 to 1990, the SSR in the Western Sichuan Plateau (WSP) increased by 0.329 W/m2 per year, affected by the decrease in aerosol and cloud, in which low clouds and dust aerosols played an important role. The SSR in SB was reduced due to the significant increase in sulfate, black carbon, and organic carbon aerosols. And aerosols in Yangtze River Delta (YRD) have important effects on SSR, while clouds were dominant for CC. From 1991 to 2018, the dominant factor influencing the SSR in WSP, SB, and CC was cloud, while the SSR in YRD was mainly determined by aerosols. From 2008 to 2018, the SSR in WSP significantly decreased by −1.188 W/m2 per year, mainly due to the increase in clouds. During this period, the SSR in YRD increases by 0.220 W/m2 per year, largely from the decrease of aerosols.

Wintertime carbonaceous species and trace metals in PM10 in Darjeeling: A high altitude town in the eastern Himalayas

Carbonaceous components [organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), primary organic carbon (POC), secondary organic carbon (SOC) and carbonaceous aerosols (CAs)] and major and trace elements (Na, Mg, Ca, Al, Fe, Ti, Cl, P, S, K, Cr, Ni, Cu, Zn, Mo and B) of PM10 were studied over the eastern Himalayan high altitude station [Darjeeling: 27.01°N and 88.15°E, 2200 m average mean sea level (amsl)] during winter 2018–19 (December 2018–February 2019). The carbonaceous aerosols/species (CAs) contributed to ~23% of PM10 mass concentration, whereas major and trace elements accounted for 10% of PM10. During the entire study period, the average concentrations of PM10, OC, EC, WSOC, POC, SOC and CAs were recorded as 48 ± 16 μg m−3, 5.39 ± 1.84 μg m−3, 2.60 ± 0.94 μg m−3, 3.87 ± 1.18 μg m−3, 3.40 ± 1.23 μg m−3, 1.99 ± 1.03 μg m−3 and 11.21 ± 3.78 μg m−3, respectively. Significant positive correlation between OC & EC and OC & WSOC have been observed which are indicating their common sources. WSOC/OC ratio was estimated to be 0.71 suggesting that the biomass burning is one of the major sources of carbonaceous aerosols at Darjeeling during winter. The significant positive correlation of PM10 with crustal elements (Al, Fe, Ca, Mg and Ti) as well as the correlation of Al with other crustal elements (Fe, Ca, Mg and Ti) indicates the abundance of mineral dust at the sampling site. Principal component analysis (PCA) identified the contribution of crustal/soil dust, biomass + coal burning, vehicular emissions and solid waste to the PM10 over the eastern Himalayan region of India.

Temporal and spatial variations of haze and fog and the characteristics of PM2.5 during heavy pollution episodes in China from 2013 to 2018

In recent years, the frequent occurrence of haze and fog events in East and Central China has caused a serious reduction in atmospheric visibility and had a huge impact on human health. Based on the relative humidity, visibility and PM2.5 concentration, the occurrence frequencies of haze as well as the spatial and temporal variations of fog, haze and mist in China from 2013 to 2018 were analyzed. The occurrence frequency of the three weather phenomena increased from 2013 until 2016, and then decreased. Regarding seasonal distribution, haze days are concentrated in winter, while mist often appears in spring and autumn. Clean fog mainly occurs in high-mountain stations and clean areas with high relative humidity, while polluted fog is more common in densely populated cities. In Beijing, the proportion of clean weather increases year by year, PM2.5 in haze weather in Beijing mainly consists of organic carbon, nitrate, sulfate and other secondary aerosols. Most fog events are accompanied by air pollution. The dominant haze is humid haze, which means that its occurrence and aggravation are usually related to aerosol hygroscopic growth.

Long term variability of carbonaceous aerosols over Southeast Asia via reanalysis: Association with changes in vegetation cover and biomass burning

In this study, we examine the seasonal variability and long–term trends in aerosol distribution over peninsular Southeast Asia (SEA: 90°–105°E, 15°–28°N) based on MERRA–2 reanalysis datasets for a period of 30 years (1985–2015). Special emphasis has been given on the loading and distribution of carbonaceous aerosols, in response to changes in vegetation cover and biomass burning over SEA. MERRA–2 reanalysis reveals a distinct seasonality in columnar AOD distribution, that peaks (0.3–0.45) in the pre-monsoon (March–May) season, with a maximum contribution from carbonaceous aerosols (~60%). The ratio of organic carbon (OC) to black carbon (BC) column mass density indicates a dominant contribution from biomass burning along with biogenic emissions (OC/BC > 10), while the OC (BC) aerosols during pre-monsoon vertically vary between ~6 and 12 μgm−3 (~0.6–1.6 μgm−3) in the lower troposphere (surface to 700 hPa) during pre-monsoon. Interestingly, linear regression in monthly variability of the enhanced vegetation index (EVI) over SEA shows a slightly increasing tendency during the recent decade (2004–2015), while the number of fire counts decreased during the same time period. In addition, a slightly positive trend in OC–AOD is likely associated with the increase in vegetation cover that contributes to the rising trend of biogenic OC emissions, while the reduction in biomass burning is linked with the declining trend of BC–AOD. The pre-monsoon average shortwave flux at the top of the atmosphere (TOA) obtained from MERRA–2 over SEA varies from −12 to −6 Wm−2 and presents a decreasing tendency during the last 30 years due to a decrease in absorbing BC fraction. The temperature anomalies are well related to changes in BC–AOD, and OC–AOD at 850 hPa level, revealing important atmospheric heating.

Deposition of brown carbon onto snow: changes in snow optical and radiative properties

Abstract. Light-absorbing organic carbon aerosol – colloquially known as brown carbon (BrC) – is emitted from combustion processes and has a brownish or yellowish visual appearance, caused by enhanced light absorption at shorter visible and ultraviolet wavelengths (0.3 µm≲λ≲0.5 µm). Recently, optical properties of atmospheric BrC aerosols have become the topic of intense research, but little is known about how BrC deposition onto snow surfaces affects the spectral snow albedo, which can alter the resulting radiative forcing and in-snow photochemistry. Wildland fires in close proximity to the cryosphere, such as peatland fires that emit large quantities of BrC, are becoming more common at high latitudes, potentially affecting nearby snow and ice surfaces. In this study, we describe the artificial deposition of BrC aerosol with known optical, chemical, and physical properties onto the snow surface, and we monitor its spectral radiative impact and compare it directly to modeled values. First, using small-scale combustion of Alaskan peat, BrC aerosols were artificially deposited onto the snow surface. UV–Vis absorbance and total organic carbon (TOC) concentration of snow samples were measured for samples with and without artificial BrC deposition. These measurements were used to first derive a BrC (mass) specific absorption (m2 g−1) across the UV–Vis spectral range. We then estimate the imaginary part of the refractive index of deposited BrC aerosol using a volume mixing rule. Single-particle optical properties were calculated using Mie theory, and these values were used to show that the measured spectral snow albedo of snow with deposited BrC was in general agreement with modeled spectral snow albedo using calculated BrC optical properties. The instantaneous radiative forcing per unit mass of total organic carbon deposited to the ambient snowpack was found to be 1.23 (+0.14/-0.11) W m−2 per part per million (ppm). We estimate the same deposition onto a pure snowpack without light-absorbing impurities would have resulted in an instantaneous radiative forcing per unit mass of 2.68 (+0.27/-0.22) W m−2 per ppm of BrC deposited.

Characteristics of methanesulfonic acid, non-sea-salt sulfate and organic carbon aerosols over the Amundsen Sea, Antarctica

Abstract. To investigate the characteristics of particulate methanesulfonic acid (MSA(p)), non-sea-salt sulfate (nss SO42-) and organic carbon (OC) aerosols, aerosol and seawater samples were collected over the Southern Ocean (43–70∘ S) and the Amundsen Sea (70–75∘ S) during the ANA06B cruise conducted in the austral summer of 2016 aboard the Korean icebreaker IBR/V Araon. Over the Southern Ocean, the atmospheric MSA(p) concentration was low (0.10±0.002 µg m−3), whereas its concentration increased sharply up to 0.57 µg m−3 in the Amundsen Sea where Phaeocystis antarctica (P. antarctica), a producer of dimethylsulfide (DMS), was the dominant phytoplankton species. Unlike MSA(p), the mean nss SO42- concentration in the Amundsen Sea was comparable to that in the Southern Ocean. Water-soluble organic carbon (WSOC) concentrations over the Southern Ocean and the Amundsen Sea varied from 0.048 to 0.16 and 0.070 to 0.18 µgC m−3, with averages of 0.087±0.038 and 0.097±0.038 µgC m−3, respectively. For water-insoluble organic carbon (WIOC), its mean concentrations over the Southern Ocean and the Amundsen Sea were 0.25±0.13 and 0.26±0.10 µgC m−3, varying from 0.083 to 0.49 and 0.12 to 0.38 µgC m−3, respectively. WIOC was the dominant organic carbon species in both the Southern Ocean and the Amundsen Sea, accounting for 73 %–75 % of the total aerosol organic carbon. WSOC/Na+ and WIOC/Na+ ratios in the fine-mode aerosol particles were higher, especially in the Amundsen Sea where biological productivity was much higher than the Southern Ocean. The fluorescence properties of water-soluble organic aerosols investigated using a fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM–PARAFAC) revealed that protein-like components were dominant in our marine aerosol samples, representing 69 %–91 % of the total intensity. Protein-like components also showed a significant positive relationship with the relative biomass of diatoms; however, they were negatively correlated with the relative biomass of P. antarctica. These results suggest that the protein-like component is most likely produced as a result of biological processes of diatoms in the Amundsen Sea.

Measurements of light-absorbing impurities in snow over four glaciers on the Tibetan Plateau

Black carbon (BC), dust, and organic carbon (OC) aerosols, when deposited onto the surface of glaciers, can absorb light and decrease the snow albedo. These impurities in snow are referred to as ILAIs (i.e., insoluble light absorbing impurities). Atmospheric chemical models have been extensively used to simulate the transport and deposition of atmospheric aerosols in glacierized areas. However, systematic investigations of ILAIs in snowpack of glaciers on the Tibetan Plateau (TP) are rare. In this study, observations of ILAIs in snow and simulations of ILAIs of atmospheric aerosol at surface over four glaciers on the TP have been analyzed. Strong correlation between BC and dust was found in surface aged-snow, and their correlation significantly varied with snowpit depth. BC and OC concentrations in snowpit tended to decrease with depth. Significant differences of ILAI concentrations among depth intervals reflect their diverse hydrophilicities, physiochemical properties and post-depositional processes in snowpit, offering important observational constraints on the related processes. Monthly variation of atmospheric ILAIs at surface over glaciers is characterized by distinct spatial heterogeneity. The statistical results show higher ILAI concentrations in the summer of 2015 than 2014, which is in qualitative agreement with CALIPSO observations, likely reflecting the effects of inter-annual variation of summer monsoon on snow ILAI loadings. Optical attenuation (ATN) of BC is gradually decreased with depth of snowpit, whereas the trend of mass absorption cross-section (MAC) of BC throughout the profile of snowpit is opposite to that of ATN. The scanning electron microscopy (SEM) imaging demonstrates that calcium and silicon rich particles dominate over biological, quartz and flying ash particles in the cryoconite, providing additional constraints on the sources of dust-in-snow and can facilitate better understanding of the physicochemical properties and climatic effects of particles in the glacial cryoconite.

Online measurements of very low elemental and organic carbon concentrations in aerosols at a subarctic remote station

Two months (Oct.–Nov. 2015) of online elemental carbon (EC) and organic carbon (OC) measurements were performed by two field OC/EC Sunset Laboratory analysers working in parallel with an 8-h time resolution at a subarctic remote station in Finland. During such a time resolution, thermal OC and EC concentrations were usually close to or below the recent limits of detection for the analyser. Thus, this work highlights the possible issues to consider during the online measurements of OC/EC analysers working at the threshold of their analytical possibilities.A detailed analysis of the data showed that even though the OC concentrations were always above the detection limit of the analyser, up to 70% of the given concentration was due to the dynamic blank (gaseous phase). The majority of the OC aerosol was present in the less volatile fractions that evolved during steps at 300–450 °C and 450–650 °C.The main bias at low EC concentrations originated from the automatically determined split point between OC and EC. The results from the RTCalc526 software often led to an early determination of the OC-EC split point, resulting in an overestimation of the EC concentrations. However, the comparison of the results was performed after processing the OC/EC raw data in the different RTCalc software versions 526 and 703. The results showed that the EC values from the newer version of the RTCalc703 software were more consistent with the equivalent black carbon (eBC) results from optical instruments (aethalometer and MAAP) measured in parallel in comparison with results from the older RTCalc526 software. Equivalent BC data from the laser attenuation measurement of the Sunset Lab. analyser also provided better agreement with the newer version of the RTCalc software (RTCalc703).

Waste timber pyrolysis in a medium-scale unit: Emission budgets and biochar quality

Pyrolysis of organic waste or woody materials yields a stable carbonaceous product that can be mixed into soil and is often termed “biochar”. During pyrolysis carbon-containing gases are emitted, mainly volatile organic carbon species, carbon monoxide and aerosols. In modern pyrolysis units, gases are after-combusted, which reduces emissions substantially. However, emission data for medium- to large-scale pyrolysis units are scant, both regarding gases, aerosols, heavy metals and polycyclic aromatic hydrocarbons (PAH).Making biochar from lightly contaminated waste timber (WT) is a promising waste handling option as it results in the potential valorization of such residues into e.g. sorbents for contaminant stabilization. For this process to be environmentally sustainable, emissions during the process need to be low and the resulting biochar of sufficient quality. To investigate both issues, we pyrolyzed three batches of WT and one reference batch of clean wood/leaves in a representative medium-scale pyrolysis unit (Pyreg-500, 750 t/year) with after-combustion of the pyrolysis gases, and measured the gas, aerosol, metal and PAH emissions, as well as the characteristics and contamination levels of the resulting biochar, including contaminant leaching.Mean emission factors for the WT were (g/kg biochar); CO = 7 ± 2, non-methane volatile organic compounds (NMVOC) = 0.86 ± 0.14, CH4 = 0, aerosols (PM10) = 0.6 ± 0.3, total products of incomplete combustion (PIC) = 9 ± 3, PAH-16 = (2.0 ± 0.2) · 10−5, As (most abundant metal) = (2.3 ± 1.9) · 10−3 and NOX = 0.65 ± 0.10. There were no significant differences in emission factors between the pyrolysis of WT and the reference respectively, except for PM10, NMVOC, and PAH-16, which were significantly lower for WT than for the clean wood/leaves. The WT biochar did not satisfy premium or basic European Biochar Certificate criteria due to high levels of zinc and PAH. However, leachable metal contents were <0.1% of total contents. Still, use of the WT-biochar without further improvement or investigation would be limited to ex situ use, not improving soil fertility or in situ remediation.

Seasonal Variation of OC, EC, and WSOC of PM10 and Their CWT Analysis Over the Eastern Himalaya

In the present study, seasonal transport trends and potential source regions of carbonaceous species [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), secondary organic carbon (SOC) and total carbonaceous aerosols (TCAs)] of PM10 was evaluated over Darjeeling, an eastern Himalayas of India during August 2018–June 2019. Backward trajectories, cluster analysis, and concentration-weighted trajectory (CWT) analysis were performed to evaluate the seasonal transport pathway of carbonaceous aerosols over the region. The annual average concentration of PM10 was recorded to be 55 ± 18 μg m−3, which is close to National Ambient Air Quality Standard (NAAQS; 60 μg m−3 for annual PM10) of India. The concentration of PM10 showed maxima in pre-monsoon season (63 ± 21 μg m−3) followed by post-monsoon (56 ± 16 μg m−3), monsoon (51 ± 13 μg m−3) and winter seasons (49 ± 17 μg m−3). The study revealed that the WSOC comprises about 72% of OC concentration with maxima in post-monsoon (81% of OC) followed by winter (74% of OC), pre-monsoon (67% of OC) and monsoon seasons (66% of OC). The concentration of SOC were estimated as 1.4 ± 0.9, 1.7 ± 1.0, 2.4 ± 0.9 and 1.9 ± 0.9 µg m−3 during pre-monsoon, monsoon, post-monsoon and winter, respectively (which are accounted for 27%, 49%, 41% and 35% to the OC mass concentration, respectively). The results indicated that biomass burning could be one of the major sources of carbonaceous aerosols in Darjeeling. Five days backward trajectory analysis (including cluster and CWT analysis) revealed that the air-mass flow of pollutants towards the sampling site of Darjeeling majorly coming from continental sites (Nepal and Indo-Gangetic plain (IGP) region of India) and the Bay of Bengal (BOB).

Characteristics and temporal variations of organic and elemental carbon aerosols in PM1 in Changchun, Northeast China.

The present study offers the first evaluation of organic and elemental carbon (OC and EC) of submicron (PM1) fraction in Changchun (Northeast China) during a year-long sampling period (October 24, 2016 to October 23, 2017). More than 288 PM1 (particulate matter with an aerodynamic diameter of less than 1μm) samples were collected. The PM1 concentrations ranged from 3.78 to 451.08μg·m-3, with an average of 57.73μg·m-3, which was 1.65 times higher than the Chinese National Standard II. Following the concept of the well-known IMPROVE algorithm, OC and EC values were obtained. The OC values ranged from 1.18 to 82.54μg∙m-3, and the EC values were from 0.30 to 14.19μg∙m-3. Total carbon (TC = EC + OC) constituted 9.11-40.35% of the total PM1 mass, and OC dominated over EC. The average OC/EC ratio was 4.78, which implied a low percentage for vehicles and a high contribution of coal and biomass consumption to PM1. Among OC, the annual primary organic carbon (POC) value was 7.69μg∙m-3, accounting for 63% of the OC, while secondary organic carbon (SOC) contributed 37% with 4.12μg∙m-3. Among EC, CHAR (EC1) dominated over SOOT (EC2 + EC3), and the CHAR/SOOR ratio ranged from 2.91 to 28.55. The results of the OC and EC values as well as the OC/EC and CHAR/SOOT ratios suggest that possible sources of PM1 include vehicles, coal burning, cooking, and biomass burning.

Large contributions of biogenic and anthropogenic sources to fine organic aerosols in Tianjin, North China

Abstract. In order to better understand the molecular composition and sources of organic aerosols in Tianjin, a coastal megacity in North China, ambient fine aerosol (PM2.5) samples were collected on a day/night basis from November to December 2016 and from May to June 2017. The organic molecular composition of PM2.5 components, including aliphatic lipids (n-alkanes, fatty acids, and fatty alcohols), sugar compounds, and photooxidation products from isoprene, monoterpene, β-caryophyllene, naphthalene, and toluene, was analysed using gas chromatography–mass spectrometry. Fatty acids, fatty alcohols, and saccharides were identified as the most abundant organic compound classes among all of the tracers detected in this study during both seasons. High concentrations of most organics at night in winter may be attributed to intensive residential activities such as house heating as well as the low nocturnal boundary layer height. Based on tracer methods, the contributions of the sum of primary and secondary organic carbon (POC and SOC respectively) to aerosol organic carbon (OC) were 24.8 % (daytime) and 27.6 % (night-time) in winter and 38.9 % (daytime) and 32.5 % (night-time) in summer. In detail, POC derived from fungal spores, plant debris, and biomass burning accounted for 2.78 %–31.6 % (12.4 %; please note that values displayed in parentheses in the following are average values) of OC during the daytime and 4.72 %–45.9 % (16.3 %) at night in winter, and 1.28 %–9.89 % (5.24 %) during the daytime and 2.08 %–47.2 % (10.6 %) at night in summer. Biomass-burning-derived OC was the predominant source of POC in this study, especially at night (16.0±6.88 % in winter and 9.62±8.73 % in summer). Biogenic SOC from isoprene, α-∕β-pinene, and β-caryophyllene exhibited obvious seasonal and diurnal patterns, contributing 2.23±1.27 % (2.30±1.35 % during the daytime and 2.18±1.19 % at night) and 8.60±4.02 % (8.98±3.67 % and 8.21±4.39 %) to OC in winter and summer respectively. Isoprene and α-∕β-pinene SOC were obviously elevated in summer, especially during the daytime, mainly due to strong photooxidation. Anthropogenic SOC from toluene and naphthalene oxidation showed higher contributions to OC in summer (21.0±18.5 %) than in winter (9.58±3.68 %). In summer, toluene SOC was the dominant contributor to aerosol OC, and biomass burning OC also accounted for a high contribution to OC, especially at night-time; this indicates that land/sea breezes also play an important role in the aerosol chemistry of the coastal city of Tianjin in North China.

Variation of carboneceous atmospheric aerosol near Saint Petersburg

The results of 5-year (20132017) measurements of organic (OC) and elemental (EC) carbon aerosol fractions observed at the atmospheric monitoring station near St. Petersburg (Petergof, 59.88 N, 29.83 E) are presented. It is shown that the site of observations is under the influence of local pollution sources most of the time (~74%). The median values of carbonaceous aerosol in polluted conditions are 0.46 g/m3 for ЕС and 2.62 g/m3 for ОС. On average, the maximum excess of the EC background level is achieved in winter (2.4 times in January). The analysis of the ratio between the OC and the EC in the total carbon indicates the predominantly anthropogenic origin of the aerosol under study. In comparison with the data of similar measurements in Central Siberia, the background summer concentrations of carbonaceous aerosol in Peterhof are significantly lower. Some episodes of increased concentrations of OC and EC are attributed to the intensive accumulation of air pollution coming from the nearby megalopolis.

Establishment of high-resolution aerosol parameterization and its influence on radiation calculations

To accurately simulate the effects of aerosols on the atmospheric radiation budget, we here establish an aerosol optical parameterization scheme with high spectral resolution (974-band) for radiative transfer model(BCC_RAD); this scheme includes sulfate (SF), black carbon (BC), organic carbon (OC), dust (SD), and sea salt (SS) aerosols. The results of the 974-band scheme are compared with those obtained using a low-resolution 17-band scheme. Our results show the 974-band scheme more accurate in its representation of the aerosols’ optical properties. The largest relative differences in the volume extinction coefficient(Kex) between the 974-band and 17-band schemes range from 5.87% to 54.64%, with BC (41.13%) and SF (54.64%) showing the largest values at 1.91 and 2.7 μm, respectively. The single scattering albedo of hygroscopic aerosols (SF, SS, and OC) show minimal values at 2.84 and 6.01 μm, respectively, in the 974-band scheme due to light absorption; however, the low spectral resolution of the 17-band scheme prevents these features from being resolved. Specifically, the relative difference between the two schemes approaches 72.72% at 2.84 μm for SF. Thus, improved spectral resolution may be required for some aerosols.We also compare the effects of aerosols on the radiation budget in East Asia simulated by 974-band and 17-band BCC_RAD models. Under clear-sky conditions, the simulation results indicate a relative difference in the radiation flux of 0.28–5.93% for the two schemes. The 974-band and 17-band schemes show daily mean direct radiative forcings (DRFs) due to all aerosols of −16.97 and −17.13 W/m2 at the surface and −7.12 and −6.93 W/m2 at the top of the atmosphere, respectively. Additionally, the 974-band model generally simulates a larger DRF for BC and smaller DRFs for scattering aerosols such as SF; these differences become greater for smaller zenith angles.

Constraining global aerosol emissions using POLDER/PARASOL satellite remote sensing observations

Abstract. We invert global black carbon (BC), organic carbon (OC) and desert dust (DD) aerosol emissions from POLDER/PARASOL spectral aerosol optical depth (AOD) and aerosol absorption optical depth (AAOD) using the GEOS-Chem inverse modeling framework. Our inverse modeling framework uses standard a priori emissions to provide a posteriori emissions that are constrained by POLDER/PARASOL AODs and AAODs. The following global emission values were retrieved for the three aerosol components: 18.4 Tg yr−1 for BC, 109.9 Tg yr−1 for OC and 731.6 Tg yr−1 for DD for the year 2010. These values show a difference of +166.7 %, +184.0 % and −42.4 %, respectively, with respect to the a priori values of emission inventories used in “standard” GEOS-Chem runs. The model simulations using a posteriori emissions (i.e., retrieved emissions) provide values of 0.119 for global mean AOD and 0.0071 for AAOD at 550 nm, which are +13.3 % and +82.1 %, respectively, higher than the AOD and AAOD obtained using the a priori values of emissions. Additionally, the a posteriori model simulation of AOD, AAOD, single scattering albedo, Ångström exponent and absorption Ångström exponent show better agreement with independent AERONET, MODIS and OMI measurements than the a priori simulation. Thus, this study suggests that using satellite-constrained global aerosol emissions in aerosol transport models can improve the accuracy of simulated global aerosol properties.

Transport of Asian aerosols to the Pacific Ocean

Abstract Recent efforts reported that the aerosols even can be transported from a long distance to the Pacific Ocean (PO) and potentially influence the marine primary productivity. In this study, based on the multi-source satellite observations and meteorological reanalysis data, the source and transport of aerosols from Asia to the PO region are investigated. The result shows that the satellites capture 104 aerosol events during 2007–2016, which occur in Asia, and can further influence the PO region. The Asian source regions of aerosol over the PO region mainly include eastern and central China (ECC), eastern and central Russia (ECR), Inner Mongolia and Gansu of China and Mongolia (IMGM), and Southeast Asia (SEA), corresponding to sulfate, organic carbon, dust, and organic carbon aerosol sources, respectively. Among the aerosol events detected over the PO region, most of them are sourced from ECC region, accounting for 54.8% of the total aerosol events, followed by ECR region (accounting for 22.1%). Statistical analyses show that, during 2007–2016, the aerosol events observed over the PO region mainly occur in the spring (47 times), followed by the autumn (25 times); and the least of them occur in the winter (14 times). Correspondingly, the months with the most and least aerosol events are March and February, respectively. When the aerosols enter the PO region, the average optical depths of aerosols sourcing from ECC, ECR, IMGM and SEA are 0.24, 0.38, 0.29 and 0.19, respectively. Besides, the transport of aerosols from Asia to the PO region is mainly influenced by westerly winds and troughs of low-pressure system. This study can provide some evidence of understanding the aerosol type, physical and optical properties over the PO region.

Retrofitting and re-powering as a control strategies for curtailment of exposure of underground miners to diesel aerosols.

A study was conducted to examine the potential of diesel emissions control strategies based on retrofitting existing power packages with exhaust aftertreatment devices and repowering with advanced power packages. The retrofit systems, a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF), were evaluated individually using a US EPA tier 2 (ter 2) engine operated under four steady-state conditions and one transient cycle. The DOC effectively curtailed emissions of CO, and to some extent organic carbon (OC), elemental carbon (EC), and aerosol number concentration. The DPF system offered substantially higher reductions in OC and EC mass and aerosol number concentrations. Both, the DOC and DPF achieved reductions in the aforementioned emissions without adversely affecting emissions of NO2 and nano-sized aerosols. The strategy of repowering with an advanced system was examined using a US EPA tier 4 final (tier 4f) engine equipped with a cooled exhaust gas recirculation system and diesel exhaust fluid-based selective catalytic reduction system, but not with a DPF system. The tier 4f engine contributed substantially less than the tier 2 engine to the EC and OC mass, aerosol number, and CO, NO, and NO2 concentrations. The tier 4f engine was very effective in reducing aerosol mass, NO, and NO2 concentrations, but it was not equally effective in reducing aerosol number concentrations. The implementation of viable exhaust after treatment systems and advanced diesel power packages could be instrumental to the underground mining industry to secure a clean, economical, and dependable source of power for mobile equipment.