PM<sub>2.5</sub> Speciation Trends Network: Evaluation of Whole-System Uncertainties Using Data from Sites with Collocated Samplers

Flanagan, James; Jayanty, R. K. M.; Rickman, Ed; Peterson, Max R.

doi:10.1080/10473289.2006.10464516

Cited by 47 publications

(33 citation statements)

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“…Monitoring System (SLAMS) such as the Speciation Trends Network (STN) (Chu et al, 2004, Flanagan et al, 2006, Interagency Monitoring of Protected Visual Environments (IMPROVE) network 2.0 (Watson et al, 2008), and the Southeastern Aerosol Research and Characterization (SEARCH) network (Hansen et al, 2006). Combined with receptor models, these methods are used to identify sources, analyze properties of the pollutants at the receptor site, and to estimate their contributions.…”

Section: Introductionmentioning

confidence: 99%

Aerosol particulate matter in the Baltimore metropolitan area: Temporal variation over a six-year period

Orozco

Delgado

Wesloh

et al. 2015

Journal of the Air & Waste Management Association

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This paper presents the first long-term aerosol speciation analysis in a Mid-Atlantic United States metropolitan area, which is essential for the air quality management agencies in order to revise regulations and reduce human exposure to adverse air quality conditions. The results suggest that although a declining trend in the overall PM2.5 was observed, no significant tendency was observed in the identified sources besides exceptional events such as the impact of wildfires on local air quality and downward contribution from industrial fraction of PM(2.5) after the Steel Mill at Sparrows Point closure in 2012.

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Section: Introductionmentioning

confidence: 99%

Aerosol particulate matter in the Baltimore metropolitan area: Temporal variation over a six-year period

Orozco

Delgado

Wesloh

et al. 2015

Journal of the Air & Waste Management Association

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“…One sigma (1σ ) precision estimates for CSN sulfate and ammonium aerosol concentrations are 6 and 8 % respectively (Flanagan et al, 2006). For the SEARCH network, the precision statistics are reported as median absolute differences (Edgerton et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol

et al. 2017

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Abstract. Thermodynamic models predict that sulfate aerosol (S(VI) ≡ H 2 SO 4 (aq) + HSO − 4 + SO 2− 4 ) should take up available ammonia (NH 3 ) quantitatively as ammonium (NH + 4 ) until the ammonium sulfate stoichiometry (NH 4 ) 2 SO 4 is close to being reached. This uptake of ammonia has important implications for aerosol mass, hygroscopicity, and acidity. When ammonia is in excess, the ammonium-sulfate aerosol ratio R = [NHshould approach 2, with excess ammonia remaining in the gas phase. When ammonia is in deficit, it should be fully taken up by the aerosol as ammonium and no significant ammonia should remain in the gas phase. Here we report that sulfate aerosol in the eastern US in summer has a low ammonium-sulfate ratio despite excess ammonia, and we show that this is at odds with thermodynamic models. The ammonium-sulfate ratio averages only 1.04 ± 0.21 mol mol −1 in the Southeast, even though ammonia is in large excess, as shown by the ammonium-sulfate ratio in wet deposition and by the presence of gas-phase ammonia. It further appears that the ammonium-sulfate aerosol ratio is insensitive to the supply of ammonia, remaining low even as the wet deposition ratio exceeds 6 mol mol −1 . While the ammonium-sulfate ratio in wet deposition has increased by 5.8 % yr −1 from 2003 to 2013 in the Southeast, consistent with SO 2 emission controls, the ammonium-sulfate aerosol ratio decreased by 1.4-3.0 % yr −1 . Thus, the aerosol is becoming more acidic even as SO 2 emissions decrease and ammonia emissions stay constant; this is incompatible with simple sulfate-ammonium thermodynamics. A tentative explanation is that sulfate particles are increasingly coated by organic material, retarding the uptake of ammonia. Indeed, the ratio of organic aerosol (OA) to sulfate in the Southeast increased from 1.1 to 2.4 g g −1 over the 2003-2013 period as sulfate decreased. We implement a simple kinetic mass transfer limitation for ammonia uptake to sulfate aerosols in the GEOS-Chem chemical transport model and find that we can reproduce both the observed ammonium-sulfate aerosol ratios and the concurrent presence of gas-phase ammonia. If sulfate aerosol becomes more acidic as OA / sulfate ratios increase, then controlling SO 2 emissions to decrease sulfate aerosol will not have the co-benefit of suppressing acidcatalyzed secondary organic aerosol (SOA) formation.

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“…Air monitoring is usually concerned with high concentrations and its practitioners thus express precision in relative, dimensionless terms. [3][4][5][6][7][8][9][10] To obtain a stable estimate of relative precision, the concentration range with uncertainties dominated by additive uncertainties must be eliminated from the estimates; however, exactly which concentrations to exclude is not clear. The additive and multiplicative uncertainties are unknown and can vary by species, site, filter lot, and even analysis date.…”

Section: Introductionmentioning

confidence: 99%

Estimating Precision Using Duplicate Measurements

Hyslop

White

2009

Journal of the Air & Waste Management Association

133

101

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Precision is a concept for which there is no universally accepted metric. Reports of precision vary depending on the formula and inclusion criteria used to calculate them. To properly interpret and utilize reported precisions, the user must understand exactly what the precision represents. This paper uses duplicate Interagency Monitoring of Protected Visual Environments (IMPROVE) measurements to illustrate distinctions among different approaches to reporting precision. Three different metrics are used to estimate the precision from the relative differences between the duplicate measurements: the root mean square (RMS), the mean absolute value, and a percentile spread. Precisions calculated using the RMS relative difference yield wide distributions that tend to overestimate most of the observed differences. Precisions calculated using percentiles of the relative differences yield narrower distributions that tend to fit the bulk of the observed differences very well. Precisions calculated using the mean absolute relative difference lie between the other two precision estimates. All three approaches underestimate the observed differences for a small percentage of outliers. INTRODUCTIONPrecision is defined by the International Standardization Organization (ISO) as "the closeness of agreement between quantity values obtained by replicate measurements of a quantity, under specified conditions…precision is usually expressed numerically by measures of imprecision, such as standard deviation, variance, or coefficient of variation under the specified conditions of measurement." 1 As noted by the ISO definition, there is no single prescribed formula for reporting precision. The quantitative expression of precision is subjectively chosen, and multiple issues must be considered when choosing a method, including whether to express the precision in dimensional or nondimensional terms, what range of concentrations to include in the precision calculations, and how to aggregate measurements made under differing conditions.

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PM_2.5 Speciation Trends Network: Evaluation of Whole-System Uncertainties Using Data from Sites with Collocated Samplers

Cited by 47 publications

References 1 publication

Aerosol particulate matter in the Baltimore metropolitan area: Temporal variation over a six-year period

Aerosol particulate matter in the Baltimore metropolitan area: Temporal variation over a six-year period

Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol

Estimating Precision Using Duplicate Measurements

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PM2.5 Speciation Trends Network: Evaluation of Whole-System Uncertainties Using Data from Sites with Collocated Samplers

Cited by 47 publications

References 1 publication

Aerosol particulate matter in the Baltimore metropolitan area: Temporal variation over a six-year period

Aerosol particulate matter in the Baltimore metropolitan area: Temporal variation over a six-year period

Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol

Estimating Precision Using Duplicate Measurements

Contact Info

Product

Resources

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PM_2.5 Speciation Trends Network: Evaluation of Whole-System Uncertainties Using Data from Sites with Collocated Samplers