Abstract
Abstract. In order to understand the aging and processing of organic aerosols (OA), an intensive field campaign (Campaign of Air Pollution at Typical Coastal Areas IN Eastern China, CAPTAIN) was conducted March–April at a receptor site (a Changdao island) in central eastern China. Multiple fast aerosol and gas measurement instruments were used during the campaign, including a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) that was applied to measure mass concentrations and non-refractory chemical components of submicron particles (PM1nr). The average mass concentration of PM1(PM1nr+black carbon) was 47 ± 36 μg m−3 during the campaign and showed distinct variation, depending on back trajectories and their overlap with source regions. Organic aerosol (OA) is the largest component of PM1 (30%), followed by nitrate (28%), sulfate (19%), ammonium (15%), black carbon (6%), and chloride (3%). Four OA components were resolved by positive matrix factorization (PMF) of the high-resolution spectra, including low-volatility oxygenated organic aerosol (LV-OOA), semi-volatile oxygenated OA (SV-OOA), hydrocarbon-like OA (HOA) and a coal combustion OA (CCOA). The mass spectrum of CCOA had high abundance of fragments from polycyclic aromatic hydrocarbons (PAHs) (m/z 128, 152, 178, etc.). The average atomic ratio of oxygen to carbon in OA (O / C) at Changdao was 0.59, which is comparable to other field studies reported at locations downwind of large pollution sources, indicating the oxidized nature of most OA during the campaign. The evolution of OA elemental composition in the van Krevelen diagram (H / C vs. O / C) showed a slope of −0.63; however, the OA influenced by coal combustion exhibits a completely different evolution that appears dominated by physical mixing. The aging of organic aerosols vs. photochemical age was investigated. It was shown that OA / ΔCO, as well as LV-OOA / ΔCO and SV-OOA / ΔCO, positively correlated with photochemical age. LV-OOA accounted for 73% of the OA secondary formation (SOA) in the oldest plumes (photochemical age of 25 h). The kOH at Changdao, by assuming SOA formation and aging as a first-order process proportional to OH, was calculated to be 5.2 × 10−12 cm3 molec.−1 s−1, which is similar to those determined in recent studies of polluted air in other continents.
Highlights
The primary sources and secondary formation of fine particles are key issues in the quantification of aerosol effects on regional air quality, climate change and human health
In order to focus on the regional contribution to fine particle concentrations at Changdao, periods strongly influenced by local coal combustion and biomass burning were excluded by recognizing concentration peaks of their corresponding indicators, naphthalene and acetonitrile, respectively
It shows that the average PM1 concentration at Changdao is about 2–4 times higher than the values measured at downwind sites in other regions, and higher than the concentrations measured at urban cities in the US and European countries
Summary
The primary sources and secondary formation of fine particles are key issues in the quantification of aerosol effects on regional air quality, climate change and human health. A major uncertainty at present are the sources, fate and aging of organic aerosols (OA), which are still not well understood due to their extremely complex composition, properties, and reaction pathways This is especially true for the secondary organic aerosols (SOA) formed from chemical reactions of gas-phase species (Hallquist et al, 2009). This study had four main objectives: (1) an overview of time series, chemical composition and size distributions of submicron particles in the continental outflow of central eastern China; (2) a study of OA primary and secondary components using positive matrix factorization (PMF) of high-resolution AMS data; (3) an analysis of bulk elemental composition (O / C, H / C and N / C) of OA; and (4) the evolution of OA, PMF components, and OA elemental ratios with photochemical age
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
