Theoretical model for the evaporation loss of PM2.5 during filter sampling

Lee

et al. 2015

Aerosol Air Qual. Res.

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In this study, long term measurements of PM 2.5 and ultrafine particles (UFPs) for daily average mass concentration at Zhongshan (ZS), Sinjhuang (SJ), and Jhudong (JD) urban air monitoring stations were conducted from 2011 spring to 2013 autumn. The results showed that daily average UFPs mass concentrations in spring (average at 3 stations: 1.58 ± 0.74 µg m -3 ) and summer (average at 3 stations: 1.59 ± 0.53 µg m -3 ) were higher than those in autumn (average at 3 stations: 1.02 ± 0.28 µg m -3 ) and winter (average at 3 stations: 1.04 ± 0.48 µg m -3 ) due to the impacts by heavy traffic emission and new particle formation event. The effective density (ρ eff ) and dynamic shape factor (χ) for ultrafine particles (UFPs) were found to be 0.68 ± 0.16 g cm -3 and 2.06 ± 0.19, respectively, suggesting that the particle morphology was irregular shape. Based on the calculated ρ eff and χ, the average number and surface area concentration ratio of UFPs to those of PM 2.5 at these monitoring stations was determined to be 89.0 ± 5.5% and 42.1 ± 12.8%, respectively, suggesting that UFPs contribute significantly to the health-relevant PM 2.5 aerosol fraction in these stations.

Section: Seasonal Variation Of Pm 25 and Ufps Mass Concentrationmentioning

confidence: 99%

Ultrafine Particles and PM2.5 at Three Urban Air Monitoring Stations in Northern Taiwan from 2011 to 2013

Lee

et al. 2015

Aerosol Air Qual. Res.

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“…S10, exposure of an unprotected acidic filter for longer than 1 d will lead to ammonia reacting with the acid to form ammonium bisulfate or ammonium sulfate, even at low ammonia mixing ratios. Other aspects that could impact this comparison and are beyond the scope of this study (but has been discussed in other studies; Hering and Cass, 1999;Schauer et al, 2003;Chow et al, 2005Chow et al, , 2010Dzepina et al, 2007;Watson et al, 2009;Nie et al, 2010;Liu et al, 2014Liu et al, , 2015Cheng and He, 2015;Heim et al, 2020) include the loss of volatile ammonium from the evaporation of ammonium nitrate or differences in the handling, shipping, and/or storage of the filters or extracted samples. Thus, without denuders, or handling of filters with more than one person present, will lead to similar differences between in situ sampling versus filter collection of inorganic aerosols observed during various aircraft campaigns.…”

Section: Impacts Of Ammonia Uptake On Acidic Filtersmentioning

confidence: 99%

“…Filter measurements have been shown to be most prone to artifacts during sample collection, handling, storage of the filter, and extraction of the aerosol from the filter prior to analysis. These artifacts include evaporation of volatile compounds such as organics (Watson et al, 2009;Chow et al, 2010;Cheng and He, 2015) and ammonium nitrate (Hering and Cass, 1999;Chow et al, 2005;Nie et al, 2010;Liu et al, 2014Liu et al, , 2015Heim et al, 2020), as well as chemical reactions of gas-phase species with the accumulated particles (e.g., Schauer et al, 2003;Dzepina et al, 2007). Further, early research indicated potential artifacts from gasphase ammonia uptake onto acidic aerosol collected onto filters, leading to a positive bias for particulate ammonium (Klockow et al, 1979;Hayes et al, 1980;Koutrakis et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Interferences with aerosol acidity quantification due to gas-phase ammonia uptake onto acidic sulfate filter samples

et al. 2020

Abstract. Measurements of the mass concentration and chemical speciation of aerosols are important to investigate their chemical and physical processing from near emission sources to the most remote regions of the atmosphere. A common method to analyze aerosols is to collect them onto filters and analyze the filters offline; however, biases in some chemical components are possible due to changes in the accumulated particles during the handling of the samples. Any biases would impact the measured chemical composition, which in turn affects our understanding of numerous physicochemical processes and aerosol radiative properties. We show, using filters collected onboard the NASA DC-8 and NSF C-130 during six different aircraft campaigns, a consistent, substantial difference in ammonium mass concentration and ammonium-to-anion ratios when comparing the aerosols collected on filters versus an Aerodyne aerosol mass spectrometer (AMS). Another online measurement is consistent with the AMS in showing that the aerosol has lower ammonium-to-anion ratios than obtained by the filters. Using a gas uptake model with literature values for accommodation coefficients, we show that for ambient ammonia mixing ratios greater than 10 ppbv, the timescale for ammonia reacting with acidic aerosol on filter substrates is less than 30 s (typical filter handling time in the aircraft) for typical aerosol volume distributions. Measurements of gas-phase ammonia inside the cabin of the DC-8 show ammonia mixing ratios of 45±20 ppbv, consistent with mixing ratios observed in other indoor environments. This analysis enables guidelines for filter handling to reduce ammonia uptake. Finally, a more meaningful limit of detection for University of New Hampshire Soluble Acidic Gases and Aerosol (SAGA) filters collected during airborne campaigns is ∼0.2 µg sm−3 of ammonium, which is substantially higher than the limit of detection of ion chromatography. A similar analysis should be conducted for filters that collect inorganic aerosol and do not have ammonia scrubbers and/or are handled in the presence of human ammonia emissions.

“…The samples are, then, extracted and mass concentrations are quantified using ion chromatography (IC). However, manual filter samplers have negative artifacts due to the semi-volatile nature of NH 4 + and NO 3 − [22] resulting in underestimation [23,24]. A porous-metal denuder sampler (PDS) [25], which uses acidic/basic coated porous metal discs to capture the basic/acidic precursor gases combined with a Teflon filter to collect particles and back-up filters to collect the semi-volatile materials evaporated from collected particles, can be used for determining the accurate mass concentrations of gases and particles simultaneously without evaporation loss [26].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Atmospheric PM2.5 Inorganic Aerosols Using the Semi-Continuous PPWD-PILS-IC System and the ISORROPIA-II

Wang

Pui

et al. 2020

Atmosphere

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A semi-continuous monitoring system, a parallel plate wet denuder and particle into liquid sampler coupled with ion chromatography (PPWD-PILS-IC), was used to measure the hourly precursor gases and water-soluble inorganic ions in ambient particles smaller than 2.5 µm in diameter (PM2.5) for investigating the thermodynamic equilibrium of aerosols using the ISORROPIA-II thermodynamic equilibrium model. The 24-h average PPWD-PILS-IC data showed very good agreement with the daily data of the manual 5 L/min porous-metal denuder sampler with R2 ranging from 0.88 to 0.98 for inorganic ions (NH4+, Na+, K+, NO3−, SO42−, and Cl−) and 0.89 to 0.98 for precursor gases (NH3, HNO3, HONO, and SO2) and slopes ranging from 0.94 to 1.17 for ions and 0.87 to 0.95 for gases, respectively. In addition, the predicted ISORROPIA-II results were in good agreement with the hourly observed data of the PPWD-PILS-IC system for SO42− (R2 = 0.99 and slope = 1.0) and NH3 (R2 = 0.97 and slope = 1.02). The correlation of the predicted results and observed data was further improved for NH4+ and NO3− with the slope increasing from 0.90 to 0.96 and 0.95 to 1.09, respectively when the HNO2 and NO2− were included in the total nitrate concentration (TN = [NO3−] + [HNO3] + [HONO] + [NO2−]). The predicted HNO3 data were comparable to the sum of the observed [HNO3] and [HONO] indicating that HONO played an important role in the thermodynamic equilibrium of ambient PM2.5 aerosols but has not been considered in the ISORROPIA-II thermodynamic equilibrium model.