scholarly journals Particulate matter (PM) episodes at a suburban site in Hong Kong: evolution of PM characteristics and role of photochemistry in secondary aerosol formation

2016 ◽  
Vol 16 (22) ◽  
pp. 14131-14145 ◽  
Author(s):  
Yi Ming Qin ◽  
Yong Jie Li ◽  
Hao Wang ◽  
Berto Paul Yok Long Lee ◽  
Dan Dan Huang ◽  
...  
Keyword(s):  
Hong Kong ◽  
Particulate Matter ◽  
Time Lag ◽  
Organic Aerosol ◽  
Meteorological Conditions ◽  
Aerosol Formation ◽  
Small Particles ◽  
Large Particles ◽  
Photochemical Aging ◽  
Suburban Site

Abstract. Episodes with high concentrations of particulate matter (PM) across the seasons were investigated during four 1-month campaigns at a suburban site in Hong Kong. High-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurements revealed that both regional transport and secondary formation contributed to high PM levels during the episodes at this site. Based on distinct meteorological conditions, episodes were categorized into three types: liquid water content (LWC), solar irradiance (IR), and long-range transport (LRT). Despite the difference in meteorological conditions, all episodes were characterized by a high fraction of sulfate (45–56 %) and organics (23–34 %). However, aerosols in LWC episodes were less aged, consisting of the lowest fraction of secondary organic aerosol (SOA) and the highest fraction of small particles. Large particles mixed internally while freshly formed small particles mixed externally in LWC episodes. Aerosols in LRT episodes, by contrast, were the most aged and consisted of the highest proportion of low-volatility oxygenated organic aerosol (LVOOA) and the lowest proportion of small particles. Both small and large particles mixed externally in LRT episodes. The highest proportion of semi-volatile oxygenated organic aerosol (SVOOA) and a medium proportion of small particles were observed in IR episodes. Both small and large particles were likely externally mixed during IR episodes. Furthermore, aerosols experienced the most dramatic size increase and diurnal variation, with a time lag between SVOOA and LVOOA and a gradual increase in carbon oxidation state (OSc ≈ 2 × O : C − H : C). Five out of 10 episodes were of the IR type, further reflecting the importance of this type of episode. The evolution of aerosol components in one particular episode of the IR type, which exhibited a clear land–sea breeze pattern, was examined in detail. Sulfate and SOA due to photochemical aging were very efficiently produced during the course of 6 h. The “less-oxidized” SOA (SVOOA) was initially formed at a higher rate than the “more-oxidized” SOA (LVOOA). The SVOOA transformed to LVOOA at the later stage of photochemical aging. This transformation was further supported by mass spectral analysis, which showed an increase in the most oxidized ion (CO2+) and decreases in moderately oxidized ones (C2H3O+, C3H3O+ and C3H5O+). By measuring the physical and chemical properties of PM in a highly time-resolved manner, the current study was able to demonstrate the dynamic and complex nature of PM transformation during high-PM episodes.

scholarly journals Particulate matter (PM) episodes at a suburban site in Hong Kong: evolution of PM characteristics and role of photochemistry in secondary aerosol formation

2016 ◽  
Author(s):  
Yi Ming Qin ◽  
Yong Jie Li ◽  
Hao Wang ◽  
Berto Paul Yok Long Lee ◽  
Dan Dan Huang ◽  
...  
Keyword(s):  
Hong Kong ◽  
Particulate Matter ◽  
Time Lag ◽  
Organic Aerosols ◽  
Meteorological Conditions ◽  
Aerosol Formation ◽  
Small Particles ◽  
Large Particles ◽  
Photochemical Aging ◽  
Suburban Site

Abstract. Episodes with high concentrations of particulate matter (PM) across the seasons were investigated during four one-month campaigns at a suburban site in Hong Kong. High-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurements revealed that both regional transport and secondary formation contributed to high PM levels during the episodes at this site. Based on distinct meteorological conditions, episodes were categorized into three types: liquid water content (LWC), solar irradiance (IR), and long-range transport (LRT). Despite the difference in meteorological conditions, all episodes were characterized by a high fraction of sulfate (45 %–56 %) and organics (23 %–34 %). However, aerosols in LWC episodes were less aged, consisting of the lowest fraction of secondary organics aerosols (SOA) and the highest fraction of small particles. Large particles mixed internally while freshly formed small particles mixed externally in LWC episodes. Aerosols in LRT episodes, by contrast, were the most aged and consisted of the highest proportion of low-volatility oxygenated organic aerosols (LVOOA) and the lowest proportion of small particles. Both small and large particles mixed externally in LRT episodes. The highest proportion of semi-volatile oxygenated organic aerosols (SVOOA) and a medium proportion of small particles were observed in IR episodes. Both small and large particles were likely externally mixed during IR episodes. Unlike in the other two types of episodes, in IR episodes aerosols experienced the most dramatic size increase and diurnal variation, with a time lag between SVOOA and LVOOA and a gradual increase in carbon oxidation state (OSc ≈ 2 × O : C – H : C). Five out of ten episodes were of the IR type, further reflecting the importance of this type of episode. The evolution of aerosol components in one particular episode of the IR type, which exhibited a clear land-sea breeze pattern, was examined in detail. Sulfate and SOA due to photochemical aging were very efficiently produced during the course of six hours. The “fresh” SOA (SVOOA) was initially formed at a higher rate than the “aged” SOA (LVOOA). The SVOOA transformed to LVOOA at the later stage of photochemical aging. This tranformation was further supported by mass spectral analysis, which showed an increase in the most oxidized ion (CO2+) and decreases in moderately oxidized ones (C2H3O+, C3H3O+ and C3H5O+). By measuring the physical and chemical properties of PM in a highly time-resolved manner, the current study was able to demonstrate the dynamic and complex nature of PM transformation during high-PM episodes.

scholarly journals Secondary organic aerosol formation from biomass burning emissions

2019 ◽  
Author(s):  
Christopher Y. Lim ◽  
David H. Hagan ◽  
Matthew M. Coggon ◽  
Abigail R. Koss ◽  
Kanako Sekimoto ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Secondary Organic Aerosol ◽  
Total Concentration ◽  
Organic Aerosol ◽  
Oh Radicals ◽  
Aerosol Formation ◽  
Atmospheric Aging ◽  
Aerosol Mass ◽  
Photochemical Aging ◽  
Organic Gases

Abstract. Biomass burning is an important source of aerosol and trace gases to the atmosphere, but how these emissions change chemically during their lifetimes is not fully understood. As part of the Fire Influence on Regional and Global Environments Experiment (FIREX 2016), we investigated the effect of photochemical aging on biomass burning organic aerosol (BBOA), with a focus on fuels from the western United States. Emissions were sampled into a small (150 L) environmental chamber and photochemically aged via the addition of ozone and irradiation by 254 nm light. While some fraction of species undergoes photolysis, the vast majority of aging occurs via reaction with OH radicals, with total OH exposures corresponding to the equivalent of up to 10 days of atmospheric oxidation. For all fuels burned, large and rapid changes are seen in the ensemble chemical composition of BBOA, as measured by an aerosol mass spectrometer (AMS). Secondary organic aerosol (SOA) formation is seen for all aging experiments and continues to grow with increasing OH exposure, but the magnitude of the SOA formation is highly variable between experiments. This variability can be explained well by a combination of experiment-to-experiment differences in OH exposure and the total concentration of non-methane organic gases (NMOGs) in the chamber before oxidation, measured by PTR-ToF-MS (r2 values from 0.64 to 0.83). From this relationship, we calculate the fraction of carbon from biomass burning NMOGs that is converted to SOA as a function of equivalent atmospheric aging time, with carbon yields ranging from 24 ± 4 % after 6 hours to 56 ± 9 % after 4 days.

scholarly journals Tracer-based source apportioning of atmospheric organic carbon and the influence of anthropogenic emissions on secondary organic aerosol formation in Hong Kong

2021 ◽  
Vol 21 (13) ◽  
pp. 10589-10608
Author(s):  
Yubo Cheng ◽  
Yiqiu Ma ◽  
Di Hu
Keyword(s):  
Hong Kong ◽  
Organic Carbon ◽  
Secondary Organic Aerosol ◽  
Large Fraction ◽  
Linear Regression Analysis ◽  
Temporal Trends ◽  
Organic Aerosol ◽  
Gas Chromatography Mass Spectrometry ◽  
Multivariate Linear Regression Analysis ◽  
Aerosol Formation

Abstract. Here we conducted comprehensive chemical characterization and source apportionment of 49 PM2.5 samples collected in Hong Kong. Besides the major aerosol constituents, 39 polar organic species, including 14 secondary organic aerosol (SOA) tracers of isoprene, monoterpenes, β-caryophyllene, and naphthalene, were quantified using gas chromatography–mass spectrometry (GC–MS). Six factors, i.e., SOA, secondary sulfate (SS), biomass burning (BB)/SOA, sea salt, marine vessels, and vehicle emissions, were apportioned by positive matrix factorization (PMF) as the major sources of ambient organic carbon (OC) in Hong Kong. The secondary formation, including OC from SOA, SS, and aging of BB plume, was the leading contributor to OC (51.4 %, 2.15 ± 1.37 µg C m−3) throughout the year. We then applied a tracer-based method (TBM) to estimate the SOA formation from the photo-oxidation of four selected precursors, and monoterpene SOA was the most abundant. A Kintecus kinetic model was used to examine the formation channels of isoprene SOA, and the aerosol-phase ring-opening reaction of isoprene epoxydiols (IEPOXs) was found to be the dominant formation pathway. Consistently, IEPOX tracers contributed 94 % to total GC–MS-quantified isoprene SOA tracers. The TBM-estimated secondary organic carbon (SOCTBM) and PMF-apportioned SOC (SOCPMF) showed similar temporal trends; however, SOCTBM only accounted for 26.5 % of SOCPMF, indicating a large fraction of ambient SOA was from other reaction pathways or precursors. Results of Pearson's R and multivariate linear regression analysis showed that NOx processing played a key role in both daytime and nighttime SOA production in the region. Moreover, sulfate had a significant positive linear relationship with SOCPMF and SS-related SOC, and particle acidity was significantly correlated with SOC from the aging of BB.

scholarly journals In situ secondary organic aerosol formation from ambient pine forest air using an oxidation flow reactor

2015 ◽  
Vol 15 (21) ◽  
pp. 30409-30471 ◽  
Author(s):  
B. B. Palm ◽  
P. Campuzano-Jost ◽  
A. M. Ortega ◽  
D. A. Day ◽  
L. Kaser ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Flow Reactor ◽  
Secondary Organic Aerosol ◽  
Ambient Air ◽  
Organic Aerosol ◽  
Pine Forest ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Aerosol Formation ◽  
Photochemical Aging

Abstract. Ambient air was oxidized by OH radicals in an oxidation flow reactor (OFR) located in a montane pine forest during the BEACHON-RoMBAS campaign to study biogenic secondary organic aerosol (SOA) formation and aging. High OH concentrations and short residence times allowed for semi-continuous cycling through a large range of OH exposures ranging from hours to weeks of equivalent (eq.) atmospheric aging. A simple model is derived and used to account for the relative time scales of condensation of low volatility organic compounds (LVOCs) onto particles, condensational loss to the walls, and further reaction to produce volatile, non-condensing fragmentation products. More SOA production was observed in the OFR at nighttime (average 4 μg m-3 when LVOC fate corrected) compared to daytime (average 1 μg m-3 when LVOC fate corrected), with maximum formation observed at 0.4–1.5 eq. days of photochemical aging. SOA formation followed a similar diurnal pattern to monoterpenes, sesquiterpenes, and toluene + p-cymene concentrations, including a substantial increase just after sunrise at 07:00 LT. Higher photochemical aging (> 10 eq. days) led to a decrease in new SOA formation and a loss of preexisting OA due to heterogeneous oxidation followed by fragmentation and volatilization. When comparing two different commonly used methods of OH production in OFRs (OFR185 and OFR254), similar amounts of SOA formation were observed. We recommend the OFR185 mode for future forest studies. Concurrent gas-phase measurements of air after OH oxidation illustrate the decay of primary VOCs, production of small oxidized organic compounds, and net production at lower ages followed by net consumption of terpenoid oxidation products as photochemical age increased. New particle formation was observed in the reactor after oxidation, especially during times when precursor gas concentrations and SOA formation were largest. Approximately 6 times more SOA was formed in the reactor from OH oxidation than could be explained by the VOCs measured in ambient air. Several recently-developed instruments quantified ambient semi- and intermediate-volatility organic compounds (S/IVOCs) that were not detected by a PTR-TOF-MS. An SOA yield of 24–80 % from those compounds can explain the observed SOA, suggesting that these typically unmeasured S/IVOCs play a substantial role in ambient SOA formation. Our results allow ruling out condensation sticking coefficients much lower than 1. Our measurements help clarify the magnitude of SOA formation in forested environments, and demonstrate methods for interpretation of ambient OFR measurements.

Secondary Organic Aerosol Formation from Urban Roadside Air in Hong Kong

2019 ◽  
Vol 53 (6) ◽  
pp. 3001-3009 ◽  
Author(s):  
Tengyu Liu ◽  
Liyuan Zhou ◽  
Qianyun Liu ◽  
Berto P. Lee ◽  
Dawen Yao ◽  
...  
Keyword(s):  
Hong Kong ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Aerosol Formation ◽  
Secondary Organic Aerosol Formation

scholarly journals Secondary organic aerosol formation exceeds primary particulate matter emissions for light-duty gasoline vehicles

2013 ◽  
Vol 13 (9) ◽  
pp. 23173-23216 ◽  
Author(s):  
T. D. Gordon ◽  
A. A. Presto ◽  
A. A. May ◽  
N. T. Nguyen ◽  
E. M. Lipsky ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Secondary Organic Aerosol ◽  
Cold Start ◽  
Organic Aerosol ◽  
Smog Chamber ◽  
Aerosol Formation ◽  
Gas Emissions ◽  
Light Duty ◽  
Gasoline Vehicles ◽  
Diesel Trucks

Abstract. The effects of photochemical aging on emissions from 15 light-duty gasoline vehicles were investigated using a smog chamber to probe the critical link between the tailpipe and ambient atmosphere. The vehicles were recruited from the California in-use fleet; they represent a wide range of model years (1987 to 2011), vehicle types and emission control technologies. Each vehicle was tested on a chassis dynamometer using the unified cycle. Dilute emissions were sampled into a portable smog chamber and then photochemically aged under urban-like conditions. For every vehicle, substantial secondary organic aerosol (SOA) formation occurred during cold-start tests, with the emissions from some vehicles generating as much as 6 times the amount of SOA as primary particulate matter after three hours of oxidation inside the chamber at typical atmospheric oxidant levels. Therefore, the contribution of light duty gasoline vehicle exhaust to ambient PM levels is likely dominated by secondary PM production (SOA and nitrate). Emissions from hot-start tests formed about a factor of 3–7 less SOA than cold-start tests. Therefore, catalyst warm-up appears to be an important factor in controlling SOA precursor emissions. The mass of SOA generated by photo-oxidizing exhaust from newer (LEV1 and LEV2) vehicles was only modestly lower (38%) than that formed from exhaust emitted by older (pre-LEV) vehicles, despite much larger reductions in non-methane organic gas emissions. These data suggest that a complex and non-linear relationship exists between organic gas emissions and SOA formation, which is not surprising since SOA precursors are only one component of the exhaust. Except for the oldest (pre-LEV) vehicles, the SOA production could not be fully explained by the measured oxidation of speciated (traditional) SOA precursors. Over the time scale of these experiments, the mixture of organic vapors emitted by newer vehicles appear to be more efficient (higher yielding) in producing SOA than the emissions from older vehicles. About 30% of the non-methane organic gas emissions from the newer (LEV1 and LEV2) vehicles could not be speciated, and the majority of the SOA formed from these vehicles appears to be associated with these unspeciated organics. These results for light-duty gasoline vehicles contrast with the results from a companion study of on-road heavy-duty diesel trucks; in that study late model (2007 and later) diesel trucks equipped with catalyzed diesel particulate filters emitted very little primary PM, and the photo-oxidized emissions produced negligible amounts of SOA.

Characterization and Source Apportionment of Organic Aerosols in Delhi, India

2020 ◽  
Author(s):  
Varun kumar ◽  
David Bell ◽  
Sophie Haslett ◽  
Deepika Bhattu ◽  
Yandong Tong ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Source Apportionment ◽  
Mass Spectrometer ◽  
Time Of Flight ◽  
Organic Aerosol ◽  
Formation Mechanisms ◽  
Aerosol Formation ◽  
Gaseous Species ◽  
Secondary Sources ◽  
Long Time

<p>Delhi is one of the world’s most polluted city and experiences very high levels of particulate matter throughout the year. It significantly affects radiative forcing, increases mortality, and causes other deleterious effects on human health. Generally, there is a lack of consensus on the dominant sources of organic aerosol driving these high aerosol concentrations. In particular, there is a need to elucidate the relative importance of primary vs. secondary sources and formation mechanisms of secondary aerosols. In order to answer questions pertaining to the sources, formation mechanisms, and atmospheric transformations of organic aerosol, we deployed for the first time in Delhi, the recently developed extractive electrospray ionization long-time-of-flight mass spectrometer (EESI-TOF) in Delhi. This was deployed along with a high-resolution long-time-of-flight aerosol mass spectrometer (AMS), and a Chemical Ionisation Mass Spectrometer fitted with a Filter Inlet for Gases and AEROsols (FIGAERO-CIMS). These measurements were further supported by measurements of black carbon and gaseous species such as CO, NO<sub>x</sub> etc.</p><p>The EESI-TOF provides in real-time information on the chemical composition at the near-molecular level without thermal desorption and fragmentation (Lopez-Hilfiker et al., 2019). It was operated in Delhi from December to February 2019. Measurements by the AMS showed persisting high levels of particulate matter. We attributed the relative contributions of different sources to total non-refractory PM mass by performing source apportionment analysis by means of positive matrix factorization (PMF). A strong day-night variability was clearly seen in all the AMS species. High levels of secondary sources during daytime e.g., low-volatility oxygenated organic aerosol (LVOOA) and an increase of factors associated with primary sources i.e., hydrocarbon-like organic aerosol (HOA) and aerosol from solid fuel combustion (SFC) during morning and evening hours was observed. A similar trend as for the primary aerosol was seen for the semi-volatile oxygenated organic aerosol (SVOOA) mainly due to increased temperature during daytime which may leads to evaporation of semi-volatile species. A unique feature observed was a significant contribution of chloride to the non-refractory (NR) PM<sub>2.5</sub> mass. On average, chloride contributed 18-20% to total NR-mass. Similar trends have also been seen in a recent study (Gani et al., 2018). The effect of these high chlorine concentrations during the night and early morning on atmospheric chemistry as well as on secondary organic aerosol formation will be presented.</p>

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