U.S. National PM_2.5 Chemical Speciation Monitoring Networks—CSN and IMPROVE: Description of networks

Figures & data

Figure 1. CSN and IMPROVE site locations are illustrated as of (a) 2006 and (b) 2012. Colocated: sites where a network had side-by-side samplers to estimate precision. Carbon backup filter: IMPROVE sites (6 in 2006 and 12 in 2012) that had a QFF backup filter to estimate the OC artifact (see text for details). All CSN sites had backup QFF for OC artifact once the IMPROVE methods (URG 3000N sampler and IMPROVE_A analysis protocol) were implemented, between 2007 and 2009; prior to implementation of the URG 3000N no sites included backup QFF. An interactive IMPROVE map with a complete site list can be found at http://views.cira.colostate.edu/fed/Tools/SiteBrowser.aspx. CSN site listing can be found at EPA (2013).

Table 1. Design specifications for IMPROVE and CSN samplers, the latter employed in EPA Speciation Trends Network

	IMPROVE	CSN
	IMPROVE,	Spiral Ambient Speciation Sampler; SASS or SuperSASS,	Reference Ambient Air Sampler (RAAS); RAAS 2.5-400,	Mass Aerosol Speciation Sampler; MASS 400 and 450,	URG 3000N Speciation Sampler^b; 3000N,
	URG	MetOne^a	Andersen	URG	URG
Sampler schematic and picture	http://vista.cira.colostate.edu/improve/Overview/IMPROVEProgram_files/v3_document.htm (see Figure 3, IMPROVE schematic)	http://www.epa.gov/ttn/amtic/files/ambient/pm25/spec/pm25pict.pdf (includes IMPROVE sampler) (see Figure 2, MetOne schematic)
External exposure	Samplers inside or under open shelter, no AC	Samplers outside, standalone units
Sampling inlet height, agl (m)	2 to 15 with most between 3 and 4	2 and 15
Sampling inlet	PM2.5 modules: weather cap. PM10: Wedding or Sierra-Andersen PM10 inlet; All Wedding inlets replaced by Sierra-Andersen in 2009	Sharp-cut cyclone with downward facing inlet nozzle; solar/weather shield	FRM PM10 inlet, modified to 48 L/min	FRM PM10 inlet	Identical to IMPROVE
Inlet cutpoint (μm); slope^c (Watson and Chow, 2011)	PM2.5 module inlet head not characterized. PM10 – 10; NA	2.5; 1.1. (Kenny et al., 2000)	10; NA	10; NA (Tolocka et al., 2001; Kenny et al., 2005)	Identical to IMPROVE
Inlet material; coating	Anodized aluminum	Anodized aluminum	Teflon-coated aluminum	Anodized aluminum; Teflon® coating optional	Identical to IMPROVE
Length of inlet tube (m); material, coating	1.83; Anodized aluminum	Cyclone inlet tube 0.34; Anodized aluminum	0.3 m; Anodized aluminum	0.3 m; Anodized aluminum	Identical to IMPROVE
PM2.5 fractionator; cutpoint (μm) (50% collection efficiency) at flow rate (L/min); slope^c (Watson and Chow, 2011)	AIHL-type cyclone; 2.4 at 22.8; 1.16 (John and Reischl, 1980)	Sharp-cut cyclone^a; 2.5 at 6.7; 1.2	AIHL-type PM2.5 cyclone; 2.3 at 24; 1.16	WINS Impactor 2.5 at 16.67; 1.18	Identical to IMPROVE
Fractionator: material; coating	Anodized aluminum	Anodized aluminum	Anodized aluminum; Teflon	Anodized aluminum; Teflon (optional)	Identical to IMPROVE
Sampler configuration – number of channels	4 individual sampling modules, each with 4 filter cassettes that can rotate	1 instrument with 5 or 8 channels, one filter canister per channel; 3 channels for CSN sampling	1 instrument with 4 channels, one filter canister per channel, 3 channels for CSN sampling	Two units with single channel, one filter canister per channel	Identical to IMPROVE
Flow splitter; split flow rates (L/min)	None	None	Inlet at 48; split 24 into two cyclones and manifold; 16.7 and 7.3 from manifold	None	None
Flow control and measurement	Orifice; pressure transducer	Mass flow controller (CSN); critical orifice	Mass flow controller	Mass flow controller; dry gas meter	Mass flow controller
Volume, temperature, and pressure reported in	Actual conditions	Actual conditions	Actual conditions	Actual conditions	Actual conditions
Number of pumps; vacuum manifold	1 per module; NA	1; all channels	1; all channels	1; NA	1; NA

Notes: ^aSpiral inlet replaced with sharp-cut cyclone (Kenny et al., 2000; Kenny and Gussman, 2000) after EPA’s chemical speciation evaluation study (Solomon et al., 2000) due to large particle penetration through spiral inlet.

^bFor organic and elemental carbon measurements. MetOne OC/EC carbon measurements using QFF replaced with the URG 3000 between mid 2007 and 2009.

^cSlope = square root of particle diameter ratios for inlet penetration at 16% and 84%.

Table 2. Filter medium (as manufacturer and model), acceptance tests, and sample preparation

Filter type	IMPROVE	CSN
PTFE/Teflon	Pall Corporation (Teflo) All filters visually inspected for holes, deformities; ˜24 filters per new lot checked for pressure drop, trace element blank levels by EDXRF^a, light absorption by HIPS Filter equilibrated at constant T and RH as noted in Table 2	Whatman (Part 7592-304) All filters visually inspected for holes, deformities; selected filters checked for weight loss or gain over time; ten filters per new lot analyzed for trace elements by EDXRF Filter equilibrated at constant T and RH as noted in Table 2
Nylon	Pall Corporation (Nylasorb) (changed from Osmonics in 2004) All filters visually inspected for holes, deformities; ˜24 filters per new lot checked for pressure drop and ion blank levels by IC Nylon filters not washed, used as received	Whatman (Part 7410-004) All filters visually inspected for holes, deformities, washed in deionized (DI) water, filter extract analyzed by IC, if extract ion concentrations exceed 0.1 μg/mL (K^+, 0.02 μg/mL) wash repeated All filters washed in DI water, dried in dedicated drying oven; 2 percent analyzed and must be less than 1% of any measured species for acceptance
QFF	Pall Corporation Pallflex (Tissuquartz) All filters visually inspected for holes, deformities; filters heat-treated and 24 filters analyzed for OC and EC by TOT and TOR Prefired at 900ºC for 4-hr	Whatman 47 mm (Part 18561-047) or Pall Corporation 25 mm (Tissuquartz 2500 QAT-UP-25MM) All filters visually inspected for holes or other deformities;  filters heat-treated, selected filters analyzed for OC and EC by TOR Prefired at 900°C for ≥ 3 hrs, cooled under N2

Notes: Shipping conditions, holding times, and laboratory storage requirements described in Table 6.

^aPESA discontinued November 2001.

Table 3. Analytical procedures by filter type and component. All measured species are listed in Table 11

	IMPROVE	CSN
PTFE/Teflon Mass	Gravimetric Equilibrated several minutes, RH = 30–50%, T = 20–25°C	Gravimetric Equilibrated 24 hr, RH = 30–40% ± 5%, T = 20–23°C ± 2°C, per FRM protocol
Filter transmittance	Hybrid integrating plate/sphere	N/A^a
Hydrogen	Proton elastic scattering analysis, discontinued January 2011	N/A
Elemental analysis	Proton-induced x-ray emission (PIXE): Na–Mn, Energy dispersive x-ray fluorescence (EDXRF): Fe–Pb through November 2001	N/A
	EDXRF: Na–Pb beginning December 2001	EDXRF for Na - Pb
Anions and cations	N/A	Ion chromatography URG MASS: Teflon front filter DI water extract, 4°C, shaken overnight, analyzed for NO3^−, SO4^2-, Na^+, NH4^+, and K^+
Nylon
Anions and cations	Ion chromatography DI water extract, room temperature overnight, second day at 4° C, analyzed for NO3^−, NO2^−, Cl^−, and SO4^2-	Ion chromatography DI water extract, 4°C, sonicate 1 hr, shaken overnight, analyzed for NH4^+, NO3^−, SO4^2-, Na^+, and K^+. URG MASS: nylon backup filter, IC eluent extract, 4°C, shaken overnight, analyzed for NO3^−
Differences between IMPROVE and CSN ionic analysis methods (both performed by the RTI Laboratory)
	IMPROVE	CSN
Extraction solution	DI H2O	DI H2O; IC eluent^c: URG nylon backup
Extraction volume^b (mL)	20	25
Sonication (min)	30	60
Mechanical shaking	None	Overnight 4°C
Additional extraction time	Second day at 4°C	None
Quartz
OC, EC, and OC and EC fractions	DRI Thermal Optical Reflectance (TOR) until 2005, modified to IMPROVE_A with TOR and TOT (Chow et al., 2007); OC and EC fractions reported in 8 temperature steps (Chow et al., 2001; Chow et al., 2008), analysis by DRI; Details in Table 4	Sunset Thermal Optical Transmittance (TOT), modified NIOSH method 5040 (RTI 2009e); OC reported in five temperature steps; Details in Table 4; By late 2009 CSN switched to IMPROVE_A method, analysis by RTI

Notes: ^aN/A, not applicable.

^bBased upon filter size (37 mm for IMPROVE; 47 mm for STN).

^cIC eluent is 0.3 mM NaHCO₃/2.7 mM Na₂CO₃.

Table 4. Operating conditions for the original CSN and the current CSN and IMPROVE OC/EC analysis protocols

	CSN/TOT^a		IMPROVE_A/TOR-TOT^b
Atmosphere/fraction	Analyte name	Maximum temperature	Analyte name	Maximum temperature
He/1st OC peak	Pk1_OC	310°C	OC1	140°C
He/2nd OC peak	Pk2_OC	480°C	OC2	280°C
He/3rd OC peak	Pk3_OC	615°C	OC3	480°C
He/4th OC peak	Pk4_OC	900°C	OC4	580°C
He-O2/PCT	Pyrol_C	Varies	OPT	580°C
He-O2/PCR	Not calculated	N/A	OPR	580°C
He&He-O2/OCT	OC^c	900°C	OCT	580°C
He&He-O2/OCR	Not calculated	N/A	OCR	580°C
He-O2/1st EC peak	Not reported	675°C	EC1	580°C
He-O2/2nd EC peak	Not reported	750°C	EC2	740°C
He-O2/3rd EC peak	Not reported	825°C	EC3	840°C
He-O2/4th EC peak	Not reported	920°C	N/A	N/A
He-O2/ECT	EC	920°C	ECT	840°C
He-O2/ECR	Not calculated	N/A	ECR	840°C

Notes: Not calculated: CSN method did not include laser reflectance values. Not reported: CSN temperature profile included the step indicated, but the data have not been reported to AQS.

^aCSN/TOT adopted by EPA in 2000 (Peterson and Richards, 2002). Switched to IMPROVE_A protocol at all sites by late 2009. Pk# refers to peak number in the thermogram since temperature step time varies.

^bIMPROVE adopted IMPROVE_A in 2005 (Chow et al., 2007); OC and EC reported using TOR and TOT. OC# and EC# refers to the OC and EC peak number in the thermogram since the temperature steps are fixed in time.

Table 5. Denuder characteristics by sampler type. Nylon channel in all samplers, see Figures 2 and 3

	IMPROVE	CSN
Sampler	IMPROVE	SASS™	RAAS	MASS	URG 3000N
Denuder type; material; active surface coating; length (m)	Annular; aluminum; Na2CO3; 0.6	Honeycomb; Al/Mg alloy; MgO; 0.025	Annular (6 surfaces); glass; MgO; 0.22	Annular (7 surfaces); glass; Na2CO3; 0.25	NA
Denuder location	Before cyclone	After cyclone before filter	After cyclone	Before WINS impactor	NA
Denuder change Frequency	Annually	3 months^a	Quarterly	Each exposure	NA
Filter cassette material; support screen material	Delrin; stainless steel screen^b (McDade et al., 2009)	Nylon & QFF: Delrin; stainless steel^c Teflon: hard plastic rings; stainless steel^d	Delrin; stainless steel^d	Delrin; stainless steel (integrated into sample module)	Delrin; stainless steel^c

Notes: ^aSix sets of denuders issued per site to accommodate rotation of MetOne canisters between laboratory and field. Each denuder replaced every 18 months, sampling 1/6 of days in that period.

^bScreen holes are larger than those in PM_2.5 FRM filter holder.

^cSame as FRM sampler.

^dAlternate material adopted when Delrin contamination observed with early lot of MetOne filter cassettes (Clark, 2002b; Gutknecht et al., 2001).

Table 6. Sampling handling, shipping conditions, holding times, and laboratory storage requirements.

	IMPROVE	CSN (MetOne)
Packing filters into cassettes	Filters loaded into filter cassettes in laboratory; cassettes capped and cartridge with up to four cassettes stored in sealed Ziploc^® bag	Filters loaded into filter cassettes with powder-free gloves in laboratory; filter canisters sealed with end caps at inlet and outlet
Presampling storage temperature (ºC)
Teflon	Ambient	4 until assembly, then ambient until sampling
Nylon	Ambient	4 until assembly, then ambient until sampling
QFF	Ambient	−15 until assembly, then ambient until sampling
Presampling holding time in sampler (hr)	24–144	12–36
Postsampling holding time (hr) in sampler	24–144	1-in-3 day sampling schedule: 24 maximum; 1-in-6 day sampling schedule: 48 maximum
Post sample shipping conditions	Ambient temperature; no temperature control, shipped in special mailer, UPS or USPS	4°C or less; shipped in special container with blue ice; overnight express shipping
Laboratory storage Temperature (°C); analysis location
Teflon	Room temperature; UC Davis	4; RTI
Nylon^a	4; RTI	4; RTI
QFF^b	−20; DRI	−20; RTI
Time in laboratory storage before analysis (days)	1–2: gravimetric analysis, variable other analyses	Teflon: If shipping <4°C, ≤30 days to postweigh; 10 business days once removed from 4°C storage
		QFF: ≤20 days upon receipt from field
		Nylon: ≤20 days upon receipt from field

Notes: ^aIMPROVE Nylon filters shipped to RTI at ambient temperature.

^bIMPROVE QFF filters sent from field to UC Davis at ambient temperature and shipped to DRI with blue ice.

Table 7. Filter characteristics, flow rates, and face velocities

	IMPROVE	CSN
Characteristic	IMPROVE	SASS™	RAAS	MASS	URG 3000N
Flow rate through filter (L/min) (nominal)	22.8 @ 20°C	6.7 per channel (module)	16.67 for Teflon channel; 7.3 for QFF and nylon channel	16.67 per channel	22.8
Filter size (outside diameter) (mm)	25 for Teflon (PM2.5 and PM10) and QFF, 37 for nylon	46.2	46.2	46.2	25
Exposed filter area Teflon^a (cm^2)	3.53 for most sites; masked to 2.20 at certain western sites with low loadings. Masks removed from all sites by 2008	11.3 [Note 1]	11.3 [Note 1]	11.3 [Notes 1 and 2]
Nylon^b (cm^2)	9.08	11.76	11.76	11.76	NA
QFF^c (cm^2)	3.53	11.76	11.76	11.76	3.38
Calculated face velocity; Teflon (cm/sec)	108.6; 174.2 (masked)	9.5	24.5	24.5	NA
Nylon (cm/sec)	43.2	9.5	10.4	24.5	NA
QFF (cm/sec)	108.6	9.5	10.4	24.5	108.6

Notes: ^aUsed to convert EDXRF analytical results from mass per unit area to mass per filter.

^bNylon filter area not required for calculations.

^cUsed to convert OC/EC analytical results from mass per unit area to mass per filter.

Note 1: 11.3 cm² area for the Teflon filter is consistent with a nominal diameter of 3.8 cm for the sampled filter diameter and used to convert EDXRF data from mass/area to mass/filter since beginning of the CSN program. 11.76 cm² value used for QFF determined in RTI’s OC/EC laboratory by repeat measurements of the inside diameters of filter cassette rings and the perforated area of the metal support screens. QFF are thicker than Teflon, so there can be significant “feathering” around the edge where the filter meets the cassette ring, which might justify using a slightly larger effective area for QFF relative to Teflon. There is approximately a 2% uncertainty in the accuracy of deposit diameter, which propagates to 4% in area.

Note 2: Cassette rings for QFF, nylon, and Teflon filters approximately identical in size for the Andersen and MetOne. URG cassette rings integrated into the filter module and have a slightly wider inside diameter than the Andersen and MetOne cassette rings. The metal support screens identical for the three CSN samplers.

Figure 2. CSN MetOne SASS sampler schematic. RAAS and MASS samplers were only used through early 2009; their schematics are available at Solomon et al. (2000) and pictures, including SASS, are available at EPA (2012c).

Figure 3. IMPROVE sampler schematic. Pictures are available at EPA (2012c).

Table 8. Recommended performance criteria used to develop data quality objectives for CSN

	Expert Panel	4-City Study	Atlanta^c	Expert Panel (R^2)	4-City Study (R^2)	Atlanta^d (r)
Species	Ratio 1 ± X%			Regression coefficient
Mass	10	10	20	≥0.9	≥0.9	≥0.9
SO4^2- or S	5	10	10	≥0.95	≥0.95	≥0.95
NO3^−	10	15	35^e	≥0.9	≥0.9	≥0.20
NH4^+	10	10	15	≥0.9	≥0.9	≥0.95
OC		15^f	20^g		≥0.9	≥0.9
EC		15^f	20^h		≥0.85	≥0.85
Trace elements	15	30	30%	≥0.85	≥0.85^i	≥0.85^j

Notes: Performance criteria recommended by EPA’s Expert Chemical Speciation Panel (Koutrakis, 1998; Koutrakis, 1999)^a, observed in the

4-City Study (Solomon et al., 2000)^b, and the Atlanta Supersites Integrated Comparison Study (Solomon et al., 2003).^b

^aExpert Panel did not provide criteria for OC and EC.

^bCriterion is ratio of test sampler to relative reference value; regression coefficient (R² for expert panel and 4-City Study; r for Atlanta), is the test sampler regressed against the relative reference or FRM depending on the study.

^cTwelve samplers including CSN in comparison. Values likely represent an outer bound for uncertainty between two sampler types.

^dRegression coefficient for Atlanta only considers CSN sampler results relative to results obtained by the FRM or for OC to the versatile air pollution sampler using a denuder to remove organic gases.

^eAverage nitrate values during the study were approximately 0.5 μg/m³, approaching the limit of detection for the method of about 0.2 μg/m³; therefore, results for nitrate likely have considerably more variability than in locations where nitrate concentrations are well above the limit of detection for the method. Compared to the relative reference value, r ≥ 0.9 could be expected.

^fGreater than 15% may be a more realistic expectation.

^gBoth samplers either with or without denuders; uncertainty increases to 35–45% if one sampler is using a denuder and the other is not.

^hWhen comparing between results using the same TOA analytical method; uncertainty increases up to 200% if comparing between different TOA methods.

ⁱFor elements (S, Si, Ca, Fe, Zn, K) measured on samples collected using the Anderson RASS as compared to elements measured on a Teflon filter collected using a PM_2.5 FRM sampler, with some exceptions. The MetOne sample in the 4-City study employed the spiral inlet, which had poor collection efficiency, was biased high for crustal-related elements, and had a correspondingly lower regression coefficients. Sulfur R² > 0.97.

^jFor higher concentration elements (S, Si, K, Ca, Fe, Zn, Pb, Cu) and r = 0.7 for Mn and 0.46 for As, all to the relative reference as defined in Solomon et al. (2003), only these 10 elements reported.

Table 9. Measurement quality objectives for the CSN and IMPROVE networks^a

	IMPROVE	CSN
Measurement^b	Acceptable range
Flow (L/min)	22.8 ± 10%	Design flow (varies by sampler type) ± 10%
Ambient temp (°C)	±10	±2
Ambient pressure (mm Hg)	±10	±10
Sample duration (min)	±5	±5
Leaks (mL/min)	<100	<100

Notes: ^aIMPROVE system audits from 2000–2006 included comparison of the reference measurement to the reported value, but not the design value. Beginning in 2007, the flow rate was checked against the design value to identify cases in which the flow rate may have been measured properly but had drifted from the design value; the flow rate was adjusted to the design value. This revision was for all parameters listed.

^bTemperature and pressure as measured using instruments in samplers.

Table 10. Trip^a and field-filter blank values for ionic species by year and sampler

		Ionic species/filter type/average concentration ± standard deviation (ng/m^3)
		NH4^+	K^+	Na^+	SO4^2-	NO3^−	NO3^−
Sampler type^b	Averaging period	Teflon (front)	Teflon (front)	Teflon (front)	Teflon (front)	Teflon (front)	Nylon (after)^c
MASS	2006 Annual	0 ± 3	0 ± 0	5 ± 8	6 ± 11	30 ± 30	28 ± 38
MASS	2006 Winter	0 ± 1	0 ± 0	2 ± 3	4 ± 6	25 ± 19	25 ± 15
MASS	2006 Spring	1 ± 3	0 ± 0	3 ± 5	3 ± 5	27 ± 17	24 ± 13
MASS	2006 Summer	0 ± 0	0 ± 0	8 ± 8	11 ± 13	26 ± 12	44 ± 71
MASS	2006 Fall	1 ± 5	0 ± 0	9 ± 11	7 ± 15	45 ± 57	20 ± 13
		NH4^+	K^+	Na^+	SO4^2-	NO3^−
		Nylon	Nylon	Nylon^d	Nylon	Nylon
RAAS	2006 Annual	1 ± 4	1 ± 6	7 ± 16	26 ± 23	21 ± 34
RAAS	2006 Winter	0 ± 2	0 ± 0	5 ± 11	21 ± 22	25 ± 40
RAAS	2006 Spring	1 ± 5	2 ± 8	4 ± 11	33 ± 30	24 ± 46
RAAS	2006 Summer	1 ± 7	0 ± 0	10 ± 20	32 ± 18	19 ± 25
RAAS	2006 Fall	0 ± 0	2 ± 10	7 ± 20	17 ± 21	14 ± 25
		NH4^+	K^+	Na^+	SO4^2-	NO3^−
		Nylon	Nylon	Nylon	Nylon	Nylon
SASS	2006 Annual	4 ± 27	1 ± 10	13 ± 158	22 ± 71	21 ± 36
SASS	2006 Winter	3 ± 21	1 ± 11	19 ± 280	23 ± 114	22 ± 34
SASS	2006 Spring	2 ± 12	1 ± 10	6 ± 22	24 ± 30	17 ± 41
SASS	2006 Summer	7 ± 41	1 ± 10	12 ± 39	24 ± 34	24 ± 34
SASS	2006 Fall	2 ± 20	1 ± 6	13 ± 49	14 ± 54	20 ± 35
SASS	2012 Annual	2 ± 7	1 ± 5	9 ± 22	34 ± 22	15 ± 33
SASS	2012 Winter	2 ± 5	1 ± 6	8 ± 19	13 ± 27	5 ± 17
SASS	2012 Spring	2 ± 11	0 ± 3	5 ± 18	42 ± 43	16 ± 48
SASS	2012 Summer	1 ± 2	1 ± 2	12 ± 26	48 ± 29	11 ± 19
SASS	2012 Fall	3 ± 4	2 ± 7	13 ± 25	31 ± 17	13 ± 25
		Cl^−	NO2^−	SO4^2-	NO3^−
		Nylon	Nylon	Nylon	Nylon
IMPROVE	2006 Annual	11 ± 8	16 ± 3	0 ± 4	12 ± 4
IMPROVE	2006 Winter	27 ± 1	18 ± 1	7 ± 6	15 ± 1
IMPROVE	2006 Spring	8 ± 1	16 ± 4	0 ± 4	9 ± 3
IMPROVE	2006 Summer	11 ± 1	14 ± 2	0 ± 0	7 ± 4
IMPROVE	2006 Fall	12 ± 1	16 ± 1	0 ± 4	12 ± 2
IMPROVE	2012 Annual	9 ± 1	13 ± 8	17 ± 5	18 ± 4
IMPROVE	2012 Winter	10 ± 1	18 ± 4	18 ± 4	20 ± 1
IMPROVE	2012 Spring	9 ± 1	0 ± 8	15 ± 3	22 ± 21
IMPROVE	2012 Summer	9 ± 1	0 ± 7	16 ± 2	15 ± 1
IMPROVE	2012 Fall	8 ± 1	17 ± 3	18 ± 10	13 ± 2

Notes: ^aCSN field and trip blanks were indistinguishable so they were averaged and the overall average reported here. CSN trip blanks were discontinued in 2013.

^bOnly CSN SASS samplers employed in the network in 2012.

^cNylon after filter was only used with the MASS sampler.

^dNylon filter washing began in early 2003.

Table 11. Minimum detection limits for CSN and IMPROVE mass and species for 2006 and 2012

	MDL (ng/m^3)^a
	Average
Species^b	CSN 2006	CSN 2012	IMPROVE 2006	IMPROVE 2012
Gravimetric
PM2.5 mass	810	840	308	307
IC (ions)
Sulfate	13	18	16	22
Nitrate	8.8	23	12	13
Nitrite	NA	NA	25	34
Chloride	NA	NA	11	6.5
Ammonium	27	26	NA	NA
Sodium	33	32	NA	NA
Potassium	25	25	NA	NA
TOT
Organic carbon	320	NA
Pk1_OC^c	320	NA
Pk2_OC	320	NA
Pk3_OC	320	NA
Pk4_OC	320	NA
PyrolC	320	NA
Elemental carbon	320	NA
TOR
OC1	NA	65	46	48
OC2	NA	65	65	90
OC3	NA	97	95	92
OC4	NA	97	47	38
OP	NA	NA	23	8.4
EC1	NA	97	23	15
EC2	NA	65	20	11
EC3	NA	65	24	0.5
EDXRF
Hydrogen	NA	NA	6.0	NA
Sodium	220	57	17	3.7
Magnesium	65	19	7.8	2.7
Aluminum	25	27	3.0	1.9
Silicon	19	19	1.3	2.8
Phosphorus	17	18	0.93	0.23
Sulfur	11	11	0.60	0.26
Chlorine	15	11	0.36	0.26
Potassium	11	11	0.20	1.1
Calcium	8.2	8.3	0.10	2.0
Scandium^b	40	NA	NA	NA
Titanium	5.8	5.8	0.05	0.30
Vanadium	4.2	4.2	0.03	0.10
Chromium	2.8	2.8	0.03	0.12
Manganese	3.6	2.9	0.03	0.25
Iron	3.4	3.4	0.04	1.4
Cobalt	2.2	2.0	NA	NA
Nickel	1.9	1.9	0.06	0.10
Copper	2.6	2.6	0.04	0.21
Zinc	3.8	8.8	0.04	0.25
Gallium^b	5.3	NA	NA	NA
Arsenic	3.8	2.8	0.09	0.19
Selenium	3.3	2.7	0.03	0.21
Bromine	3.1	2.5	0.03	0.20
Rubidium	3.4	2.8	0.05	0.28
Strontium	3.9	3.8	0.08	0.24
Yttrium	4.7	NA	NA	NA
Zirconium^b	5.6	25	0.13	1.2
Niobium^b	6.5	NA	NA	NA
Molybdenum^b	9.7	NA	NA	NA
Silver	16	40	NA	NA
Cadmium	20	24	NA	NA
Indium	24	35	NA	NA
Tin	34	39	NA	NA
Antimony	45	56	NA	NA
Cesium	57	47	NA	NA
Barium	92	60	NA	NA
Lanthanum^b	110	NA	NA	NA
Cerium^b	130	NA	NA	NA
Samarium^b	10	NA	NA	NA
Europium^b	18	NA	NA	NA
Terbium^b	12	NA	NA	NA
Hafnium^b	41	NA	NA	NA
Tantalum^b	30	NA	NA	NA
Tungsten^b	21	NA	NA	NA
Iridium^b	9.2	NA	NA	NA
Gold^b	8.3	NA	NA	NA
Mercury^b	10	NA	NA	NA
Lead	8.5	6.4	0.05	0.62

Notes: For CSN, concentrations are based on the MetOne flow rate of 6.7 L/min and for IMPROVE at 22.8 L/min, both assuming 24-hr sampling period. MDL calculations methods are given in Table 13.

^aMDLs are given in ambient concentration (ng/m³); however, since the RAAS and MASS operated at higher flow rates, the effective MDLs will be proportionately lower than for the SASS.

^bThe number of elements analyzed by EDXRF for CSN was reduced from 48 to 33, and elements labeled are no longer reported.

^cPk#_OC corresponds to the OC fractions, OC1–OC4, and PyrolC refers to pyrolytic carbon.

Table 12. Carbon artifact concentrations based on a nominal flow rates for CSN and IMPROVE and assuming a 24-hr sample: for CSN, average of trip and field blank samples; for IMPROVE, median of QFF after filter values

		Average concentration (ng/m^3)^a
Sampler type		OC	EC	OC1	OC2	OC3	OC4
MASS	2006 Annual	346	3	91	144	85	22
MASS	2006 Winter	376	4	85	155	109	25
MASS	2006 Spring	280	0	51	88	52	16
MASS	2006 Summer	425	3	106	186	99	28
MASS	2006 Fall	360	3	126	144	69	20
RAAS	2006 Annual	920	7	283	352	217	63
RAAS	2006 Winter	917	3	300	321	227	60
RAAS	2006 Spring	771	3	230	332	170	36
RAAS	2006 Summer	1032	17	278	385	273	91
RAAS	2006 Fall	906	6	310	367	171	54
SASS	2006 Annual	1035	8	289	421	250	70
SASS	2006 Winter	970	4	300	376	229	62
SASS	2006 Spring	864	3	212	371	214	63
SASS	2006 Summer	1188	8	294	470	329	89
SASS	2006 Fall	1078	18	342	467	202	62
URG 3000N	2012 Annual	130	3	14	43	65	8
URG 3000N	2012 Winter	122	3	14	38	63	7
URG 3000N	2012 Spring	139	3	12	48	70	9
URG 3000N	2012 Summer	132	2	14	46	63	8
URG 3000N	2012 Fall	130	3	14	42	65	9
IMPROVE	2006 Annual	NR	NR	53	77	93	20
IMPROVE	2006 Winter	NR	NR	51	63	72	9
IMPROVE	2006 Spring	NR	NR	59	77	103	21
IMPROVE	2006 Summer	NR	NR	58	101	158	40
IMPROVE	2006 Fall	NR	NR	43	69	84	18
IMPROVE	2012 Annual	NR	NR	17	64	91	19
IMPROVE	2012 Winter	NR	NR	22	56	67	12
IMPROVE	2012 Spring	NR	NR	17	72	98	21
IMPROVE	2012 Summer	NR	NR	17	89	120	32
IMPROVE	2012 Fall	NR	NR	20	53	70	13

Notes: NR: not reported.

^aZero indicates the reported average is below the MDL.

Table 13. Overview of MDL calculations for CSN^a and IMPROVE

Analysis method	CSN	IMPROVE
Gravimetry	Three times the standard deviation of ˜ 50 filters per lot received and acceptance tested, typically annually or more often	Twice the analytical uncertainty; a constant analytical uncertainty is applied, determined previously from laboratory weighing controls
Ion chromatography	Three times the standard deviation of ionic species concentrations measured on ˜7 laboratory blanks; MDLs are determined annually	Two times the standard deviation of ionic species concentrations measured on 45 field blanks collected each month
Thermal optical analysis	Three times the standard deviation of the instrument MDL provided by the manufacturer based on analysis of a large number of filters	Two times the standard deviation of OC and EC concentrations measured on 60 secondary filters collected each month
EDXRF	Three times the average instrument counting uncertainty for each element based on the analysis of ten new lot blanks; MLD values determined with each new filter lot of Teflon filters	Prior to 2011, MDL was estimated as 3.29 times the square root of the background counts under the region that would have been occupied by a peak of normal width (IMPROVE, 1997); expressed as ng/cm^2; beginning in 2011, with the change to the PANalytical instrument, MDL is estimated based on the 95th percentile of the intensity measured on a set of 50 to 100 field blank (IMPROVE, 2014a)

Notes: ^aEmployed since June 2003. See text for prior to June 2003.

Table 14. Data completeness estimates for CSN and IMPROVE from 2006 and 2012 by year and analytical method

	IMPROVE		CSN
Analysis method	2006	2012	2006	2012
Mass	92	94	94	96
Anions (all species)	92	94	95	96
Cations: NH4^+	N/A	N/A	95	96
Cations: Na^+ and K^+	N/A	N/A	95	96
OC/EC (all fractions)	94	94	95	94
EDXRF (all elements)	92	94	95	96

Note: N/A, not measured.

Table 15. Precision estimates for major components as percent average relative difference between colocated samplers

	CSN^a (2006) (%)	CSN^a (2012) (%)	IMPROVE (2006) (%)	IMPROVE (2012) (%)	Comments
Mass	20	13	11	7
Sulfate	18	7	7	3
Nitrate	20	8	8	7
Ammonium	16	11	N/A	N/A
Sodium*	40 (ion)	20 (ion)	N/A	N/A	^*Na^+ ion by IC and
	31 (elemental)	19 (elemental)	61	35	elemental Na by EDXRF
Potassium*	19 (ion)	22 (ion)	N/A	N/A	^*K^+ ion by IC and elemental K by EDXRF OC and EC fractions not reported in CSN
	20 (elemental)	13 (elemental)	N/A	N/A
Organic carbon	24	6	14	9
OC1	N/A	N/A	42	48
OC2	N/A	N/A	21	16
OC3	N/A	N/A	17	15
OC4	N/A	N/A	18	18
OCP	N/A	N/A	29	30
Elemental carbon	17	9	1424	13
EC1	N/A	N/A	**	21
EC2	N/A	N/A	**	130
EC3	N/A	N/A		**
Fe	30	18	18	14
Ca	31	23	19	16
Si	31	22	32	17
Al	41	27	44	18
Ti	28	28	26	20
V	22	19	30	25
Ni	30	28	29	30
Pb	25	20	23	27
Zn	33	16	22	16
Cd	**	**	N/A	N/A

Notes: N/A, not measured.

^aPrecision estimates are given for species where the ambient concentrations were greater than 3 times their MDL.

**Less than 10 valid sample pairs; average not calculated.

Table 16. Startup history and summary of changes in field and laboratory network operations since 2000 when CSN began initial operations

Date (year/month)	Change in network operations	Reason for change
IMPROVE 1988	20 sites established in Class 1 Areas
1999	Network increased to 30 IMPROVE and 40 IMPROVE Protocol sites
2000–2002	Network increased to 110 IMPROVE sites in Class I areas and 57 Protocol sites with funding from EPA	The network was expanded to meet the needs of the Regional Haze Rule and in support of CSN objectives
2000/10	Nylon filters extracted using IC anion eluent (0.3 mM NaHCO3/2.7 mM Na2CO3) at all sites except GRSM1, SHEN1, and DOSO1 where filters were extracted with DI water. Previously nylon filters extracted some years in eluent, some years in water
2001/04	Nylon filters extracted using DI water at all sites	To reduce blank levels and allow for the measurement of ammonium ion if desired. Provided consistency with CSN
2001/12	Analysis of elements from Na to Mn was changed from PIXE to EDXRF by Cu anode	Improved detection limits for most elements of interest, plus better sample preservation for reanalysis
2002/06	Changed from quarterly to monthly medians to estimate OC artifact corrections from field blanks and QFF backup filters	To obtain an improved estimate of the OC artifact since the artifact varied by season and within season
2002/10	Standardized EDXRF run times changed from variable times to a standard 1000 sec	A single standardized exposure time was selected, providing acceptable detection limits for all elements of interest
2004/01	Changed nylon filter supplier from Osmonics to Pall Corporation	Field blank concentrations were decreased substantially, especially for chloride
2005/01	Changed carbon analysis instrument from DRI/OGC to model 2001 Thermal/Optical Carbon Analyzer (Desert Research Institute) Changed analysis protocol from IMPROVE to IMPROVE_A	To replace obsolete equipment. New equipment provided better temperature control and more stable analysis environment. (Chow et al., 2007)
2005/01	Changed from He flush to vacuum with Cu anode for the EDXRF system	He diffused through the Be window of the SiLi detector, changing the calibration and eventually destroying the detector
2008/08	Number of samplers with carbon backup filters increased from 6 to 12. Used to determine carbon artifact corrections	To obtain an improved estimate of the OC artifact since artifact varied by region due to differences in ambient conditions
2011/01	EDXRF analysis switched from custom-built legacy systems to PANalytical Epsilon 5	MDLs improved for many elements, x-ray self-absorption correction no longer applied, several spectral interferences eliminated
2011/01	PESA analysis discontinued, used to quantify hydrogen	Due to reduced funding
CSN
2000	Pilot study of 13 sites established and operated through July 2000
2001/1–2005/10	Network increased January 2001 through October 2005 to 54 STN and 181 SLAMS and Tribal sites, with 28 SLAMS IMPROVE protocol sites
2002/02	Improved nylon filter washing procedures	Higher levels of sodium and nitrate seen in filters as supplied from manufacturer. Washing reduced contamination
2003	Implemented improved OC/EC thermogram software that reduced background noise and improved blank levels. Samples reported before this date were reprocessed using the new software and resubmitted to AQS (reprocessing and reposting done in 2007)	Software was upgraded by vendor and implemented on RTI’s analyzers as part of normal system upgrades
2003/6	Prior to June 2003, a single set of MDL values (ng/m^3) for each species and sampler type was reported in AQS for CSN. After June 2003, MDL values were reported with each concentration value in AQS	Changed to be more consistent with IMPROVE reporting of MDL values
2006/01	Lighter weight shipping containers integrated into CSN network (fully implemented by March 2006). Initially composed of reinforced corrugated cardboard; changed after a short period to corrugated plastic boxes with longer lifetimes and about the same weight	Filter temperatures were maintained at 4°C or better because of the new shipping containers. Shipping costs were reduced
2006/04	Network reductions began in 2005; CSN reduced to 54 STN and 159 SLAMS, 28 IMPROVE Protocol, 3 Tribal sites	Due to reduced funding
2007/3–2009/9	Transition to URG 3000N sampler and IMPROVE_A method for carbon analysis on QFF	Requested by EPA to remove differences observed between the two networks for OC and EC
2009	Last MASS and RASS Samplers replaced by SASS samplers (2009/02 for last MASS, 2009/04 for last RASS)	Improved uniformity across network and reduced costs associated with multiple sampler types
2009	Number of elements analyzed by EDXRF reduced from 48 to 33 (see Table 12)	Elements removed were seldom seen above the MDL in field measurements
2009	EDXRF attenuation correction implemented for Na, Mg, Al, P, and Si (see text for details)	EPA added XRF attenuation corrections to the new CSN analytical contract
2013/1	Trip blanks discontinued	Due to reduced funding. Trip blanks were statistically similar to field blanks (the latter continued)

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