Physical and chemical characterization of ambient aerosol by HR‐ToF‐AMS at a suburban site in Hong Kong during springtime 2011

Abstract. Aerosol pollution has been a very serious environmental problem in China for many years. The volatility of aerosols can affect the distribution of compounds in the gas and aerosol phases, the atmospheric fates of the corresponding components, and the measurement of the concentration of aerosols. Compared to the characterization of chemical composition, few studies have focused on the volatility of aerosols in China. In this study, a thermodenuder aerosol mass spectrometer (TD-AMS) system was deployed to study the volatility of non-refractory submicron particulate matter (PM 1 ) species during winter in Shenzhen. To our knowledge, this paper is the first report of the volatilities of aerosol chemical components based on a TD-AMS system in China. The average PM 1 mass concentration during the experiment was 42.7±20.1 µg m −3 , with organic aerosol (OA) being the most abundant component (43.2 % of the total mass). The volatility of chemical species measured by the AMS varied, with nitrate showing the highest volatility, with a mass fraction remaining (MFR) of 0.57 at 50 • C. Organics showed semivolatile characteristics (the MFR was 0.88 at 50 • C), and the volatility had a relatively linear correlation with the TD temperature (from the ambient temperature to 200 • C), with an evaporation rate of 0.45 % • C −1 . Five subtypes of OA were resolved from total OA using positive matrix factorization (PMF) for data obtained under both ambient temperature and high temperatures through the TD, including a hydrocarbonlike OA (HOA, accounting for 13.5 %), a cooking OA (COA, 20.6 %), a biomass-burning OA (BBOA, 8.9 %), and two oxygenated OAs (OOAs): a less-oxidized OOA (LO-OOA, 39.1 %) and a more-oxidized OOA (MO-OOA, 17.9 %). Different OA factors presented different volatilities, and the volatility sequence of the OA factors at 50 • C was HOA (MFR of 0.56) > LO-OOA (0.70) > COA (0.85) ≈ BBOA (0.87) > MO-OOA (0.99), which was not completely consistent with the sequence of their O / C ratios. The high volatility of HOA implied that it had a high potential to be oxidized to secondary species in the gas phase. The aerosol volatility measurement results in this study provide useful parameters for the modeling work of aerosol evolution in China and are also helpful in understanding the formation mechanisms of secondary aerosols.

Section: Source Apportionment Methodssupporting

confidence: 83%

Volatility measurement of atmospheric submicron aerosols in an urban atmosphere in southern China

Cao

Huang

et al. 2018

“…Mass spectra of organic aerosols measured by HR-ToF-AMS were also analyzed by PMF with an analysis toolkit Ulbrich et al, 2009;Zhang et al, 2011). Three factors, namely hydrocarbon-like organic aerosol (HOA), semi-volatile oxygenated organic aerosols (SVOOA), and low-volatility oxygenated organic aerosols (LVOOA), were resolved by PMF (Lee et al, 2013, and Section 2 in supporting information). The two OOA factors have been considered as surrogates for SOA and will be used in the following discussion, along with other indicators including f 44 (fraction of m/z 44 in organic mass spectra) (Ng et al, 2010), the elemental ratio of oxygen to carbon (O : C) (Aiken et al, 2008), and the carbon oxidation state (OS c ) (Kroll et al, 2011) in order to evaluate the degree of oxygenation of OA.…”

Section: Discussionmentioning

confidence: 99%

Evaluating the degree of oxygenation of organic aerosol during foggy and hazy days in Hong Kong using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS)

Lee

et al. 2013

Abstract. The chemical characteristics of organic aerosol (OA) are still poorly constrained. Here we present observation results of the degree of oxygenation of OA based on high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) measurements made at a coastal site in Hong Kong from late April to the end of May in 2011. Two foggy periods and one hazy period were chosen for detailed analysis to compare the changes in the degree of oxygenation of OA due to different processes. Using HR-ToF-AMS measured inorganic species as input, the Extended Aerosol Inorganic Model (E-AIM) predicted a fine-particle liquid water content (LWCfp) up to 85 μg m−3 during the foggy days. Particle concentration as measured by HR-ToF-AMS was up to 60 μg m−3 during the hazy days and up to 30 μg m−3 during the foggy days. The degree of oxygenation of OA, as indicated by several parameters including the fraction of m/z 44 in organic mass spectra (f44), the elemental ratio of oxygen to carbon (O : C), and the carbon oxidation state (OSc), was evaluated against the odd oxygen (Ox) concentration, LWCfp, ionic strength (IS), and in situ pH (pHis). Observations suggest that the high concentration of OA (on average 11 μg m−3) and the high degree of oxygenation (f44 = 0.15, O : C = 0.51, and OSc = −0.31) during the hazy period were mainly due to gas-phase oxidation. During the foggy periods with low photochemical activities, the degree of oxygenation of OA was almost as high as that on the hazy days, and significantly higher than that during non-foggy/non-hazy days. However, the OA evolved quite differently in the two foggy periods. The first foggy period in late April saw a larger LWCfp and a lower Ox concentration and the OA were made up of ~ 20 % semi-volatile oxygenated organic aerosol (SVOOA) as resolved by positive matrix factorization (PMF). In the second foggy period in mid-May, higher Ox concentration and lower LWCfp were observed, and the OA were found to contain > 50 % low-volatility oxygenated organic aerosols (LVOOA). An examination of the particle characteristics (pHis, IS, and LWCfp) suggests that partitioning may have been the dominating process through which oxygenated species were incorporated into the particle phase during the first foggy period, while oxidation in the aqueous phase dominated over gas-phase processes during the second foggy period.

“…The high-resolution mode only analyzed the signals with m/z below 200. AMS calibrations -including ionization efficiency (IE) calibration, flow rate calibration and size calibration -were used as well as data quality assurance protocols (DeCarlo et al, 2006;Lee et al, 2013;Schurman et al, 2015). IE calibrations with differential mobility analyzer (DMA) size-selected (mobility diameter, D m = 400 nm) pure ammonium nitrate particles were carried out weekly.…”

Section: Measurementsmentioning

confidence: 99%

Impacts of traffic emissions on atmospheric particulate nitrate and organics at a downwind site on the periphery of Guangzhou, China

Qin

Tan

et al. 2017

Self Cite

Abstract. Particulate matter (PM) pollution on the peripheries of Chinese megacities can be as serious as in cities themselves. Given the substantial vehicular emissions in inner-city areas, the direct transport of primary PM (e.g., black carbon and primary organics) and effective formation of secondary PM from precursors (e.g., NO x and volatile organic compounds) can contribute to PM pollution in "buffer" zones between cities. To investigate how traffic emissions in inner-city areas impact these adjacent buffer zones, a suite of real-time instruments were deployed in Panyu, downwind from central Guangzhou, from November to December 2014. Nitrate mass fraction was higher on high-PM days, with the average nitrate-to-sulfate ratio increasing from around 0.35 to 1.5 as the PM mass concentration increased from 10 to 160 µg m −3 . Particulate nitrate was strongly correlated with excess ammonium (([NHwith higher concentrations in December than in November due to lower temperatures. The organic mass fraction was the highest across all PM 1 levels throughout the campaign. While organic aerosols (OA) were dominated by secondary organic aerosols (SOA = semi-volatile oxygenated organic aerosols + low-volatility oxygenated organic aerosols) as a campaign average, freshly emitted hydrocarbon-like organic aerosols (HOA) contributed up to 40 % of OA during high-OA periods, which typically occurred at nighttime and contributed 23.8 to 28.4 % on average. This was due to daytime traffic restrictions on heavy-duty vehicles in Guangzhou, and HOA almost increased linearly with total OA concentration. SOA increased as odd oxygen (O x = O 3 + NO 2 ) increased during the day due to photochemistry. A combination of nighttime traffic emissions and daytime photochemistry contributed to the buildup of PM in Panyu. The mitigation of PM pollution in inner-city areas by reducing vehicular traffic can potentially improve air quality in peripheral areas.