Secondary Aerosol Production Research Articles

The impact of hydrogenated vegetable oil (HVO) on the formation of secondary organic aerosol (SOA) from in-use heavy-duty diesel vehicles

This manuscript contains an assessment of tailpipe emissions and secondary aerosol formation from two in-use heavy-duty diesel vehicles (HDDVs) with different aftertreatment systems when operated with ultra-low sulfur diesel (ULSD) and hydrogenated vegetable oil (HVO) operated on a chassis dynamometer. Secondary aerosol formation was characterized from the HDDVs' diluted exhaust collected and photochemically aged in a 30 m3 mobile atmospheric chamber. Primary nitrogen oxide (NOx) and particulate matter (PM) emissions were reduced for both vehicles operating on HVO compared to ULSD. For the vehicles with no selective catalytic reduction (SCR) system, secondary aerosol production was ~2 times higher for ULSD compared to HVO. The composition of primary aerosol was exclusively organic for the vehicle with no SCR system regardless of fuel type. The composition of secondary aerosol with HVO was primarily organic for the vehicle equipped with diesel particulate filter (DPF)/SCR system; however, when the same vehicle was tested with ULSD, the composition was ~20% organic (80% ammonium nitrate). The results reported here revealed that the in-use vehicle with no-SCR had a non-functioning DPF leading to dramatic increases in secondary aerosol formation when compared to the DPF/SCR vehicle. The high-resolution mass spectra analysis showed that the POA of HVO combustion contained relatively lower portion of CH class compounds (or higher CHO class compounds) compared to ULSD under the similar conditions, which can be rationalized by the higher cetane number of HVO. Substantial growth of oxidized organic aerosol (such as m/z 44 peak) were observed after 5 h of photochemical oxidation, consistent with aged organic aerosols present in the atmosphere. The C4H9+ fragment at m/z 57 peak was used as a tracer to calculate evolution of secondary organic aerosol formation.

Fine particle pH and its influencing factors during summer at Mt. Tai: Comparison between mountain and urban sites

Fine particle pH plays an important role in aerosol chemistry. Understanding of influencing factors and evolution process of fine particle pH is helpful to facilitate the improvement of air quality management strategies. Here, we performed simultaneously field measurement at Mt. Tai and the surrounding urban site during the summer of 2018, and analyzed comprehensively fine particle pH and its driving factors based on the sensitivity tests. The results indicated that ambient temperature (Temp), atmospheric relative humidity (RH), TNH3 (= NH4+ + NH3) and SO42− were the dominant factors for fine particle pH. The switch between RH-sensitive and Temp-sensitive regimes with variation of RH at the mountain site implied that fine particle pH was more sensitive to RH at Mt. Tai. Elevated TNH3 could not sufficiently raise fine particle pH to neutral at relatively high SO42− levels, whereas had a significant effect on fine particle pH when SO42− concentration was relatively low. Considering the current levels of TNH3 in summer of the North China Plain (NCP), fine particle pH was more sensitive to SO42− at present. However, the sensitive factor of fine particle pH in the future is expected to shift from SO42− to TNH3 with declining SO2 emissions and increasing NH3 emissions, leading in turn to the evident increase of fine particle pH. Elevated fine particle pH and abundant TNH3 may enhance secondary inorganic aerosol production, and thus effectively synergetic control of SO2 and NH3 is urgently needed to be considered in the NCP and even in other regions of China.

Substantial changes in gaseous pollutants and chemical compositions in fine particles in the North China Plain during the COVID-19 lockdown period: anthropogenic vs. meteorological influences

Abstract. The rapid response to the COVID-19 pandemic led to unprecedented decreases in economic activities, thereby reducing the pollutant emissions. A random forest (RF) model was applied to determine the respective contributions of meteorology and anthropogenic emissions to the changes in air quality. The result suggested that the strict lockdown measures significantly decreased primary components such as Cr (−67 %) and Fe (−61 %) in PM2.5 (p<0.01), whereas the higher relative humidity (RH) and NH3 level and the lower air temperature (T) remarkably enhanced the production of secondary aerosol, including SO42- (29 %), NO3- (29 %), and NH4+ (21 %) (p<0.05). The positive matrix factorization (PMF) result suggested that the contribution ratios of secondary formation (SF), industrial process (IP), biomass burning (BB), coal combustion (CC), and road dust (RD) changed from 36 %, 27 %, 21 %, 12 %, and 4 % before the COVID-19 outbreak to 44 %, 20 %, 20 %, 9 %, and 7 %, respectively. The rapid increase in the contribution ratio derived from SF to PM2.5 implied that the intermittent haze events during the COVID-19 period were characterized by secondary aerosol pollution, which was mainly contributed by the unfavorable meteorological conditions and high NH3 level.

Using an oxidation flow reactor to understand the effects of gasoline aromatics and ethanol levels on secondary aerosol formation

Fuel type and composition affect tailpipe emissions and secondary aerosol production from mobile sources. This study assessed the influence of gasoline fuels with varying levels of aromatics and ethanol on the primary emissions and secondary aerosol formation from a flexible fuel vehicle equipped with a port fuel injection engine. The vehicle was exercised over the LA92 and US06 driving cycles using a chassis dynamometer. Secondary aerosol formation potential was measured using a fast oxidation flow reactor. Results showed that the high aromatics fuels led to higher gaseous regulated emissions, as well as particulate matter (PM), black carbon, and total and solid particle number. The high ethanol content fuel (E78) resulted in reductions for the gaseous regulated pollutants and particulate emissions, with some exceptions where elevated emissions were seen for this fuel compared to both E10 fuels, depending on the driving cycle. Secondary aerosol formation potential was dominated by the cold-start phase and increased for the high aromatics fuel. Secondary aerosol formation was seen in lower levels for E78 due to the lower formation of precursor emissions using this fuel. In addition, operating driving conditions and aftertreatment efficiency played a major role on secondary organic and inorganic aerosol formation, indicating that fuel properties, driving conditions, and exhaust aftertreatment should be considered when evaluating the emissions of secondary aerosol precursors from mobile sources.

Design and characterization of a new oxidation flow reactor for laboratory and long-term ambient studies

Abstract. Oxidation flow reactors (OFRs) are frequently used to study the formation and evolution of secondary aerosol (SA) in the atmosphere and have become valuable tools for improving the accuracy of model simulations and for depicting and accelerating realistic atmospheric chemistry. Driven by rapid development of OFR techniques and the increasing appreciation of their wide application, we designed a new all-Teflon reactor, the Particle Formation Accelerator (PFA) OFR, and characterized it in the laboratory and with ambient air. A series of simulations and experiments were performed to characterize (1) flow profiles in the reactor using computational fluid dynamics (CFD) simulations, (2) the UV intensity distribution in the reactor and the influence of it and varying O3 concentration and relative humidity (RH) on the resulting equivalent OH exposure (OHexp), (3) transmission efficiencies for gases and particles, (4) residence time distributions (RTDs) for gases and particles using both computational simulations and experimental verification, (5) the production yield of secondary organic aerosol (SOA) from oxidation of α-pinene and m-xylene, (6) the effect of seed particles on resulting SA concentration, and (7) SA production from ambient air in Riverside, CA, US. The reactor response and characteristics are compared with those of a smog chamber (Caltech) and of other oxidation flow reactors: the Toronto Photo-Oxidation Tube (TPOT), the Caltech Photooxidation Flow Tube (CPOT), the TUT Secondary Aerosol Reactor (TSAR), quartz and aluminum versions of Potential Aerosol Mass reactors (PAMs), and the Environment and Climate Change Canada OFR (ECCC-OFR). Our studies show that (1) OHexp can be varied over a range comparable to that of other OFRs; (2) particle transmission efficiency is over 75 % in the size range from 50 to 200 nm, after minimizing static charge on the Teflon surfaces; (3) the penetration efficiencies of CO2 and SO2 are 0.90 ± 0.02 and 0.76 ± 0.04, respectively, the latter of which is comparable to estimates for LVOCs; (4) a near-laminar flow profile is expected based on CFD simulations and suggested by the RTD experiment results; (5) m-xylene SOA and α-pinene SOA yields were 0.22 and 0.37, respectively, at about 3 × 1011 molec. cm−3 s OH exposure; (6) the mass ratio of seed particles to precursor gas has a significant effect on the amount of SOA formed; and (7) during measurements of SA production when sampling ambient air in Riverside, the mass concentration of SA formed in the reactor was an average of 1.8 times that of the ambient aerosol at the same time.

Effects of driving conditions on secondary aerosol formation from a GDI vehicle using an oxidation flow reactor

A comprehensive study on the effects of photochemical aging on exhaust emissions from a vehicle equipped with a gasoline direct injection engine when operated over seven different driving cycles was assessed using an oxidation flow reactor. Both primary emissions and secondary aerosol production were measured over the Federal Test Procedure (FTP), LA92, New European Driving Cycle (NEDC), US06, and the Highway Fuel Economy Test (HWFET), as well as over two real-world cycles developed by the California Department of Transportation (Caltrans) mimicking typical highway driving conditions. We showed that the emissions of primary particles were largely depended on cold-start conditions and acceleration events. Secondary organic aerosol (SOA) formation also exhibited strong dependence on the cold-start cycles and correlated well with SOA precursor emissions (i.e., non-methane hydrocarbons, NMHC) during both cold-start and hot-start cycles (correlation coefficients 0.95–0.99), with overall emissions of ∼68–94 mg SOA per g NMHC. SOA formation significantly dropped during the hot-running phases of the cycles, with simultaneous increases in nitrate and ammonium formation as a result of the higher nitrogen oxide (NOx) and ammonia emissions. Our findings suggest that more SOA will be produced during congested, slow speed, and braking events in highways.

Effects of renewable fuel and exhaust aftertreatment on primary and secondary emissions from a modern heavy-duty diesel engine

Compared to petroleum diesel, renewable diesel fuels and exhaust aftertreatment systems can reduce primary exhaust emissions that are hazardous to human health and the environment. Secondary aerosol emissions which form upon atmospheric processing have, however, been less studied. This study aimed to quantify the impacts of replacing petroleum diesel with renewable fuels (hydrotreated vegetable oil [HVO] and rapeseed methyl ester [RME]) on primary and secondary aerosol emissions from a heavy-duty diesel engine at different stages of an exhaust aftertreatment system. Emission characterization was obtained by combining a battery of physical characterization techniques with chemical characterization using aerosol mass spectrometry.At engine-out measurements, RME and HVO reduced primary particulate matter (PM) emissions (for example equivalent black carbon [eBC]) and secondary aerosol production (studied with an oxidation flow reactor [OFR]) by mass compared to petroleum diesel. The diesel oxidation catalyst (DOC) reduced primary nucleation mode emissions, reduced the effective density of soot mode emissions, and reduced secondary particle production by mass. The DOC + a diesel particulate filter removed >99% of the particle number and eBC emissions.Volatile PM emissions (for example organic aerosol) were found to be distributed between the nucleation mode and soot mode for both primary and secondary emissions, to a degree that depends on both fuel type and aftertreatment. A high mass concentration of condensable species and a low condensation sink in the soot mode led to increased fractions of condensable species present in the nucleation mode. Aging in the OFR led to increases in particle effective density. Motoring the engine (running without combustion) showed that the nucleation mode originated primarily from lubricating oil, and nonvolatile nanoparticle emissions were identified down to 1.2 nm in particle size.In conclusion, replacing petroleum diesel with HVO and RME changes emission characteristics and can help reduce key aerosol emissions of relevance for adverse health and climate impact, especially for diesel engines with no or limited exhaust aftertreatment.

Variability of surface aerosol properties at an urban site in Beijing based on two years of in-situ measurements

Aerosol optical properties are important indices for monitoring atmospheric aerosol pollution. In this study, we report the seasonal and diurnal variability of major aerosol optical parameters, including scattering coefficient (σs), absorbing coefficient (σa), single scattering albedo (SSA), together with PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) and PM10 (particulate matter with aerodynamic diameter ≤ 10 μm) mass concentrations measured at an urban site in Beijing from September 2017 to August 2019. The relationships between these aerosol properties with meteorological conditions, in particular, the mixing layer height (MLH), wind speed, and wind direction, are further investigated. Results show that the annual average values of PM2.5 and PM10 mass concentrations, σs, and σa during the study period are 54 ± 54 μg/m3, 100 ± 72 μg/m3, 170 ± 180 Mm−1, 17 ± 15 Mm−1 respectively, which are much lower than those previously reported, indicating the effectiveness of strict pollution control strategies implemented in recent years. SSA is calculated with σs and σa, whose annual average value is 0.88 ± 0.07. Seasonally, σa exhibits dual peaks except in summer, PM2.5 and PM10 concentrations are the highest value in the spring, whereas σs has the highest value in the summer with a secondary peak in the spring. The diurnal cycle of σa is highly anti-correlated with that of the MLH. For σs, PM2.5 and PM10, their diurnal cycles often peak around noon and are in phase with the MLH in the spring and summer, which may be associated with the photochemical production of secondary aerosols. σs, σa, PM10, and PM2.5 concentrations are inversely related to wind speed, but PM10 starts to increase as wind speed exceeds 4 m/s, possibly caused by dust and catkins. The increase in wind speed also weakens the aerosol-MLH relationship. Back trajectory analysis indicates that high aerosol concentrations are mostly associated with southward and westward airmasses.

Investigation of factors controlling PM2.5 variability across the South Korean Peninsula during KORUS-AQ.

The Korea – United States Air Quality Study (May – June 2016) deployed instrumented aircraft and ground-based measurements to elucidate causes of poor air quality related to high ozone and aerosol concentrations in South Korea. This work synthesizes data pertaining to aerosols (specifically, particulate matter with aerodynamic diameters <2.5 micrometers, PM2.5) and conditions leading to violations of South Korean air quality standards (24-hr mean PM2.5 < 35 μg m−3). PM2.5 variability from AirKorea monitors across South Korea is evaluated. Detailed data from the Seoul vicinity are used to interpret factors that contribute to elevated PM2.5. The interplay between meteorology and surface aerosols, contrasting synoptic-scale behavior vs. local influences, is presented. Transboundary transport from upwind sources, vertical mixing and containment of aerosols, and local production of secondary aerosols are discussed. Two meteorological periods are probed for drivers of elevated PM2.5. Clear, dry conditions, with limited transport (Stagnant period), promoted photochemical production of secondary organic aerosol from locally emitted precursors. Cloudy humid conditions fostered rapid heterogeneous secondary inorganic aerosol production from local and transported emissions (Transport/Haze period), likely driven by a positive feedback mechanism where water uptake by aerosols increased gas-to-particle partitioning that increased water uptake. Further, clouds reduced solar insolation, suppressing mixing, exacerbating PM2.5 accumulation in a shallow boundary layer. The combination of factors contributing to enhanced PM2.5 is challenging to model, complicating quantification of contributions to PM2.5 from local versus upwind precursors and production. We recommend co-locating additional continuous measurements at a few AirKorea sites across South Korea to help resolve this and other outstanding questions: carbon monoxide/carbon dioxide (transboundary transport tracer), boundary layer height (surface PM2.5 mixing depth), and aerosol composition with aerosol liquid water (meteorologically-dependent secondary production). These data would aid future research to refine emissions targets to further improve South Korean PM2.5 air quality.

Rapid improvement in air quality due to aerosol-pollution control during 2012–2018: An evidence observed in Kunshan in the Yangtze River Delta, China

China's severe air pollution was widely concerned in the past decade. A rigorous emission control has been implemented by the Chinese government since 2013. It is essential to evaluate changes of air pollutants to understand effectiveness of present air-pollution control on improving air quality. Here, we investigate temporal trends of air pollutants, including PM2.5, SO2, NO2 and O3, observed at 12 sites over the Kunshan area in the Yangtze River Delta region during 2012–2018 using Mann-Kendall statistical test. Overall, significant reduction trends of monthly PM2.5 (−7.4% yr−1) were observed, together with reduction in the PM2.5 to CO ratio (−5.8% yr−1), an indicator of secondary aerosol production. Secondary aerosol precursors, SO2 (−10.3% yr−1) and NO2 (−4.4% yr−1) also presented statistically significant reduction trends. These results reflect the consequence of emission control that leads to substantial reduction in the bulk PM2.5 concentration, as well as secondary aerosols likely formed from SO2 and NO2. However, O3 had statistically significant increase trend (+3.4% yr−1) during 2014–2018. Limited formation of O3 under high PM2.5 and NO2 concentrations condition was found at daytime in summer, which might reflect one of the reasons causing the increase trend of O3 under the current reduction scenario of PM2.5 and NO2. Potential source contribution function analysis demonstrated that the transport from the regions located to northwest of Kunshan could contribute to high concentrations of PM2.5 in all seasons, while the south and southeast could be the high potential as source areas for O3.

Intermediate and high ethanol blends reduce secondary organic aerosol formation from gasoline direct injection vehicles

We evaluated the secondary aerosol formation from two current technology flex fuel vehicles (FFVs) equipped with gasoline direct injection engines when operated on different fuel formulation on a chassis dynamometer. This study explored the influence of ethanol fueling and aromatic concentration on secondary organic aerosol (SOA) production by utilizing two E10 fuels with different aromatic levels and two higher ethanol blends (i.e., E30 and E78). The diluted emissions from both FFVs were photooxidized in a 30 m3 mobile atmospheric chamber with two distinct initial conditions, while the vehicles operated over cold-start and hot-start LA92 test cycles. Testing revealed that one vehicle did not produce secondary aerosol when emissions were photooxidized with a single precursor oxidant. However significant SOA formation occurred in the presence of an anthropogenic volatile organic carbon surrogate and NOx mixture in the chamber, despite the fact that both vehicles had similar primary particulate emission levels. The secondary aerosol formed in an urban airshed was mainly composed of ammonium nitrate and significantly exceeded primary tailpipe PM emissions. Cold-start operation from both vehicles led to greater secondary aerosol production compared to hot-start LA92 operation. SOA production showed a strong relationship with the tailpipe non-methane hydrocarbon (NMHC) emissions and overall reduced with higher ethanol blending in the fuel. The impact of aromatics was clear, with the higher aromatic E10 fuel showing higher SOA formation than the lower aromatic E10 fuel.

Quantification of the impact of cooking processes on indoor concentrations of volatile organic species and primary and secondary organic aerosols.

Cooking is recognized as an important source of particulate pollution in indoor and outdoor environments. We conducted more than 100 individual experiments to characterize the particulate and non‐methane organic gas emissions from various cooking processes, their reaction rates, and their secondary organic aerosol yields. We used this emission data to develop a box model, for simulating the cooking emission concentrations in a typical European home and the indoor gas‐phase reactions leading to secondary organic aerosol production. Our results suggest that about half of the indoor primary organic aerosol emission rates can be explained by cooking. Emission rates of larger and unsaturated aldehydes likely are dominated by cooking while the emission rates of terpenes are negligible. We found that cooking dominates the particulate and gas‐phase air pollution in non‐smoking European households exceeding 1000 μg m−3. While frying processes are the main driver of aldehyde emissions, terpenes are mostly emitted due to the use of condiments. The secondary aerosol production is negligible with around 2 μg m−3. Our results further show that ambient cooking organic aerosol concentrations can only be explained by super‐polluters like restaurants. The model offers a comprehensive framework for identifying the main parameters controlling indoor gas‐ and particle‐phase concentrations.

Light Absorption by Ambient Black and Brown Carbon and its Dependence on Black Carbon Coating State for Two California, USA, Cities in Winter and Summer

AbstractObservations from a wintertime and summertime field campaign are used to assess the relationship between black and brown carbon (BC and BrC, respectively) optical properties and particle composition and coating state. The wintertime campaign, in Fresno, CA, was impacted by primary emissions from residential wood burning, secondary organic and inorganic particle formation, and BC from motor vehicles. Two major types of BrC were observed in wintertime. One occurred primarily at night—the result of primary biomass burning emissions. The second was enhanced in daytime and strongly associated with particulate nitrate and the occurrence of fog. The biomass‐burning‐derived BrC absorbed more strongly than the nitrate‐associated BrC but had a weaker wavelength dependence. The wintertime BC‐specific mass absorption coefficient (MACBC) exhibited limited dependence on the ensemble‐average coating‐to‐BC mass ratio (Rcoat‐rBC) at all wavelengths, even up to Rcoat‐rBC of ~5. For the summertime campaign, in Fontana, CA, BC dominated the light absorption, with negligible BrC contribution even after substantial photochemical processing. The summertime MACBC exhibited limited dependence on Rcoat‐rBC, even up to ratios of &gt;10. Based on the four classes of BC‐containing particles identified by Lee et al. (2017, https://doi.org/10.5194/acp‐17‐15055‐2017) for the summertime measurements, the general lack of an absorption enhancement can be partly—although not entirely—attributed to an unequal distribution of coating materials between the BC‐containing particle types. These observations demonstrate that in relatively near‐source environments, even those impacted by strong secondary aerosol production, the ensemble‐average, mixing‐induced absorption enhancement for BC due to coatings can be quite small.

Impact of biogenic emissions on early summer ozone and fine particulate matter exposure in the Seoul Metropolitan Area of Korea

Understanding how ozone (O3) and fine particulate matter (PM) formation respond to the precursor concentrations in the presence of biogenic emissions (BEs) and thereby changes in health effects can be a key step to design effective air quality management plans. This is particularly true in the Seoul Metropolitan Area (SMA), where future significant controls of anthropogenic sources of O3 and PM2.5 precursors are expected. In this paper, we investigate the effects of BEs on O3 and fine PM (PM2.5) concentrations during a strong photochemical air pollution season in the SMA in Korea. O3 and PM2.5 levels are modeled with and without BEs in June 2008. Further, we perform the health impact assessments (HIA) of O3 and PM2.5 concentration changes due to BEs to seek useful implications for air quality management by utilizing the adjusted exposure concentration fields for O3 and PM2.5 with an observation fusing (OBF) method. With BEs, daily maximum 8-h average O3 (maximum 8-h O3) and secondary organic aerosol (SOA) concentrations in the SMA increase by 17 and 474%, respectively. These increments are associated with significant consumption of photochemical oxidants (Ox), such as a ~ 60% reduction in OH∙ radicals. The reduction in Ox, conversely, lowers the production of secondary inorganic aerosols (SIOAs) by 2.7%. Adjusted O3 and PM2.5 exposure metrics and the subsequent HIA reveal that large mean increments of O3, about 8.43 ppb, due to BEs are responsible for approximately 62 all-cause premature mortalities in the SMA in June. However, mean increment of PM2.5 due to BEs is approximately 0.3 μg m−3 and results in negligible impacts on the all-cause mortality. Significant correlations of O3 and mortality rates (MR) with the VOC/NOx ratios across the SMA suggest that controlling volatile organic compounds (VOCs) from anthropogenic sources can be a priority to reduce O3 levels and population health risks in the SMA. Specifically, linear relationships of log [O3] and log [MR] to log [VOC/NOx] ensure that a 10% decrease in the VOC/NOx ratios through the VOC abatements would lead to a 1.5% decrease in the O3 levels and a 4.3% decrease in the MR on average across the SMA.

Evolution in physiochemical and cloud condensation nuclei activation properties of crop residue burning particles during photochemical aging.

As a main form of biomass burning in agricultural countries, crop residue burning is a significant source of atmospheric fine particles. In this study, the aging of particles emitted from the burning of four major crop residues in China was investigated in a smog chamber. The particle size distribution, chemical composition and cloud condensation nuclei (CCN) activity were simultaneously measured. The properties of crop residue burning particles varied substantially among different fuel types. During aging, the particle size and mass concentration increased substantially, suggesting condensational growth by formation of secondary aerosols. The particle composition was dominated by organics. Aging resulted in considerable enhancement of organics and inorganics, with enhancement ratios of 1.24-1.44 and 1.33-1.76 respectively, as well as a continuous increase in the oxidation level of organics. Elevated CCN activity was observed during aging, with the hygroscopicity parameter κ varying from 0.16 to 0.34 for fresh particles and 0.19 to 0.40 for aged particles. Based on the volume mixing rule, the hygroscopicity parameter of organic components (κorg) was derived. κorg exhibited an increasing tendency with aging, which was generally consistent with the tendency of the O:C ratio, indicating that the oxidation level was related to the hygroscopicity and CCN activity of organic aerosols from crop residue burning. Our results indicated that photochemical aging could significantly impact the CCN activation of crop burning aerosols, not only by the production of secondary aerosols, but also by enhancing the hygroscopicity of organic components, thereby contributing to the aerosol indirect climate forcing.

Particulate Matter and Gaseous Pollutions in Three Metropolises along the Chinese Yangtze River: Situation and Implications.

The situation of criteria atmospheric pollutants, including particulate matter and trace gases (SO2, NO2, CO and O3), over three metropolises (Chongqing, Wuhan, and Nanjing), representing the upstream, midstream and downstream portions of the Yangtze River Basin from September 2015 to August 2016 were analyzed. The maximum annual mean PM2.5 and PM10 concentrations were 61.3 and 102.7 μg/m3 in Wuhan, while highest annual average gaseous pollutions occurred in Nanjing, with 49.6 and 22.9 ppb for 8 h O3 and NO2, respectively. Compared to a few years ago, SO2 and CO mass concentrations have dropped to well below the qualification standards, and the O3 and NO2 concentrations basically meet the requirements though occasionally is still high. In contrary, about 13%, 25%, 22% for PM2.5, and 4%, 17%, 15% for PM10 exceed the Chinese Ambient Air Quality Standard (CAAQS) Grade II. Particulate matter, especially PM2.5, is the most frequent major pollutant to poor air quality with 73%, 64% and 88% accounting for substandard days. Mean PM2.5 concentrations on PM2.5 episode days are 2–3 times greater than non-episode days. On the basis of calculation of PM2.5/PM10 and PM2.5/CO ratios, the enhanced particulate matter pollution on episode days is closely related to secondary aerosol production. Except for O3, the remaining five pollutants exhibit analogous seasonal patterns, with the highest magnitude in winter and lowest in summer. The results of back trajectories show that air pollution displays synergistic effects on local emissions and long range transport. O3 commonly demonstrated negative correlations with other pollutants, especially during winter, while moderate to strong positive correlation between particulate matter and NO2, SO2, CO were seen. Compared to pollutant substandard ratios over three megacities in eastern China (Beijing, Shanghai, and Guangzhou), the situation in our studied second-tier cities are also severe. The results in this paper provide basic knowledge for pollution status of three cities along Chinese Yangtze River and are conductive to mitigating future negative air quality levels.

Primary emissions and secondary aerosol production potential from woodstoves for residential heating: Influence of the stove technology and combustion efficiency

To reduce the influence of biomass burning on air quality, consumers are encouraged to replace their old woodstove with new and cleaner appliances. While their primary emissions have been extensively investigated, the impact of atmospheric aging on these emissions, including secondary organic aerosol (SOA) formation, remains unknown. Here, using an atmospheric smog chamber, we aim at understanding the chemical nature and quantify the emission factors of the primary organic aerosols (POA) from three types of appliances for residential heating, and to assess the influence of aging thereon. Two, old and modern, logwood stoves and one pellet burner were operated under typical conditions. Emissions from an entire burning cycle (past the start-up operation) were injected, including the smoldering and flaming phases, resulting in highly variable emission factors. The stoves emitted a significant fraction of POA (up to 80%) and black carbon. After ageing, the total mass concentration of organic aerosol (OA) increased on average by a factor of 5. For the pellet stove, flaming conditions were maintained throughout the combustion. The aerosol was dominated by black carbon (over 90% of the primary emission) and amounted to the same quantity of primary aerosol emitted by the old logwood stove. However, after ageing, the OA mass was increased by a factor of 1.7 only, thus rendering OA emissions by the pellet stove almost negligible compared to the other two stoves tested. Therefore, the pellet stove was the most reliable and least polluting appliance out of the three stoves tested. The spectral signatures of the POA and aged emissions by a High Resolution – Time of Flight – Aerosol Mass Spectrometer (Electron Ionization (EI) at 70 eV) were also investigated. The m/z 44 (CO2+) and high molecular weight fragments (m/z 115 (C9H7+), 137 (C8H9O2+), 167 (C9H11O3+) and 181 (C9H9O4+, C14H13+)) correlate with the modified combustion efficiency (MCE) allowing us to discriminate further between emissions generated from smoldering vs flaming conditions.

Synergistic effect among Cl2, SO2 and NO2 in their heterogeneous reactions on gamma-alumina

Severe haze in China has been a global concern in recent years. Most studies about the mechanism of haze formation mare only focused on the heterogeneous reactions of SO2 and NO2 on mineral aerosols. However, little is known about the role of molecular chlorine (Cl2) in those reactions. Here, we investigated the heterogeneous uptake of Cl2, SO2 and NO2 on γ-Al2O3 particles under different conditions using a quartz-based flow reactor. We found that the existence of γ-Al2O3 seed aerosols significantly promotes the formation of secondary chloride, sulfate and nitrate aerosols, and Cl2, NO2 and SO2 have synergistic effects when they react on γ-Al2O3 surface under humid condition. The results also shows that Cl2 can promote the formation of secondary sulfate and nitrate aerosols on γ-Al2O3 surface. Moreover, Cl2 is much easier to react with the surface of γ-Al2O3 and form secondary Cl− aerosol when comparing with NO2 and SO2, suggesting that Cl2 is of great importance in atmospheric chemistry, it has the potential to alter the surface properties (e.g., chemical composition and fraction) of mineral aerosol, enhance the production of secondary inorganic aerosols in the troposphere, and thus cause adverse effects on the climate and human health.

Simulated impacts of direct radiative effects of scattering and absorbing aerosols on surface layer aerosol concentrations in China during a heavily polluted event in February 2014

AbstractWe quantified aerosol direct radiative effects on surface layer concentrations of aerosols during a heavily polluted event in the North China Plain (NCP, 35.4°N–41.2°N, 113.3°E–119.3°E) during 21–27 February 2014, using the chemistry version of the Weather Research and Forecasting (WRF‐Chem) Model. Comparisons of model results with observations showed that the WRF‐Chem model reproduced the spatial and temporal variations of meteorological variables reasonably well, but overestimated average PM2.5 concentration by 21.7% over the NCP during 21–27 February. The simulated direct radiative effects of total, absorbing, and scattering aerosols reduced the planetary boundary layer (PBL) heights by 111.4 m, 35.7 m, and 70.7 m, respectively, averaged over NCP and 21–27 February. The direct radiative effects of total aerosols induced increases in aerosol concentrations by 11.5% for , 29.5% for , 29.6% for , 28.7% for organic carbon (OC), 26.7% for black carbon (BC), and 20.4% for PM2.5, respectively, averaged over the NCP during 21–27 February 2014. The increase in PM2.5 concentration averaged over the NCP and the haze event was 29.6 μg m−3 (16.8%) due to radiative effect of scattering aerosols, as a result of the decreases in PBL height and changes in secondary aerosol production rates. The corresponding increase in PM2.5 concentration owing to absorbing aerosols was 2.1 μg m−3 (1.0%), resulting from the offsetting impacts of changes in PBL height, wind near the surface, and chemical processes.

Sources and atmospheric processing of winter aerosols in Seoul, Korea: insights from real-time measurements using a high-resolution aerosol mass spectrometer

Abstract. Highly time-resolved chemical characterization of nonrefractory submicrometer particulate matter (NR-PM1) was conducted in Seoul, the capital and largest metropolis of Korea, using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The measurements were performed during winter, when elevated particulate matter (PM) pollution events are often observed. This is the first time that detailed real-time aerosol measurement results have been reported from Seoul, Korea, and they reveal valuable insights into the sources and atmospheric processes that contribute to PM pollution in this region. The average concentration of submicron aerosol (PM1 = NR-PM1+ black carbon (BC)) was 27.5 µg m−3, and the total mass was dominated by organics (44 %), followed by nitrate (24 %) and sulfate (10 %). The average atomic ratios of oxygen to carbon (O / C), hydrogen to carbon (H / C), and nitrogen to carbon (N / C) of organic aerosols (OA) were 0.37, 1.79, and 0.018, respectively, which result in an average organic mass-to-carbon (OM / OC) ratio of 1.67. The concentrations (2.6–90.7 µg m−3) and composition of PM1 varied dynamically during the measurement period due to the influences of different meteorological conditions, emission sources, and air mass origins. Five distinct sources of OA were identified via positive matrix factorization (PMF) analysis of the HR-ToF-AMS data: vehicle emissions represented by a hydrocarbon-like OA factor (HOA, O / C = 0.06), cooking activities represented by a cooking OA factor (COA, O / C = 0.14), wood combustion represented by a biomass burning OA factor (BBOA, O / C = 0.34), and secondary organic aerosol (SOA) represented by a semivolatile oxygenated OA factor (SV-OOA, O / C = 0.56) and a low-volatility oxygenated OA factor (LV-OOA, O / C = 0.68). On average, primary OA (POA = HOA + COA + BBOA) accounted for 59 % the OA mass, whereas SV-OOA and LV-OOA contributed 15 and 26 %, respectively. Our results indicate that air quality in Seoul during winter is influenced strongly by secondary aerosol formation, with sulfate, nitrate, ammonium, SV-OOA, and LV-OOA together accounting for 64 % of the PM1 mass during this study. However, aerosol sources and composition were found to be significantly different between clean and polluted periods. During stagnant periods with low wind speed (WS) and high relative humidity (RH), PM concentration was generally high (average ±1σ = 43.6 ± 12.4 µg m−3) with enhanced fractions of nitrate (27 %) and SV-OOA (8 %), which suggested a strong influence from local production of secondary aerosol. Low-PM loading periods (12.6 ± 7.1 µg m−3) tended to occur under higher-WS and lower-RH conditions and appeared to be more strongly influenced by regional air masses, as indicated by higher mass fractions of sulfate (12 %) and LV-OOA (20 %) in PM1. Overall, our results indicate that PM pollutants in urban Korea originate from complex emission sources and atmospheric processes and that their concentrations and composition are controlled by various factors, including meteorological conditions, local anthropogenic emissions, and upwind sources.