Source appointment of nitrogen in PM_2.5 based on bulk δ¹⁵N signatures and a Bayesian isotope mixing model

Figures & data

Table 1. δ¹⁵N values (mean ± SD) reported for major NO_x and NH₃ emissions in the atmosphere.

Sources	N species	δ^15N/‰	References
Coal combustion	NO2	+19.8 ± 5.2	Felix et al. (2012)
Coal combustion	NH3	−8.9 ± 4.1	Freyer (1991), Felix et al. (2013)
Vehicle exhausts	NO2	−2.5 ± 1.5	Walters et al. (2015)
Vehicle exhausts	NH3	−3.4 ± 1.7	Felix et al. (2013)
Biomass burning	NO2	+12.5 ± 3.1	Hastings et al. (2009), Felix et al. (2012)
Biomass burning	NH3	+12.0	Kawashima and Kurahashi (2011)
Microbial N cycle	NO2	−30.3 ± 9.4	Li and Wang (2008), Felix et al. (2013), Felix and Elliott (2014)
Animal wastes	NH3	−19.0 ± 14.1	Freyer (1978), Heaton (1987), Felix et al. (2013, 2014)
Fertilizer application	NH3	−26.8 ± 15.4	Felix et al. (2013, 2014)

Fig. 1. δ¹⁵N values of bulk N in PM_2.5 and dominant N sources assigned for PM_2.5 at the Beijing CRAES site (in red) and the Menyuan site (in blue). The box encompasses the 25th–75th percentiles, whiskers are SD values. The line and square in each box mark the median and arithmetic mean values, respectively. The number of jittered replicate δ¹⁵N data (dots around the boxes) is 1–34. Mean and SD values of source δ¹⁵N data were used in the SIAR model. δ¹⁵N values of N from dust were assumed as those of surface soils (Wang et al., 2014) according to the air mass backward trajectories (Fig. 2).

Table 2. Mass concentrations of inorganic N (–N plus –N), –S, bulk N, molecular ratios of to , to , to () in PM_2.5 at Beijing (CRAES site) and a background site (Menyuan, Qinghai province) of China. Data of ambient NH₃ and SO₂ at Beijing site were cited from Carmichael et al. (2003), He et al. (2014), Wei et al. (2015). Data of NH₃ and SO₂ were cited from the background site of Waliguan in Qinghai Province (Carmichael et al., 2003).

	Beijing (CRAES site)	Menyuan, Qinghai
PM2.5 (μg/m^3)	264.3 ± 118.0 (43.0–433.6)	13.0 ± 3.2 (7.0–17.8)
-N (%)	7.4 ± 3.4 (3.5–12.9)	5.9 ± 1.8 (3.1–9.4)
-N (%)	5.0 ± 3.0 (0.7–9.4)	1.9 ± 0.4 (1.2–2.6)
-S (%)	5.5 ± 2.4 (2.4–8.3)	0.2 ± 0.0 (0.2–0.3)
Inorganic N (%)	12.4 ± 4.6 (5.1–22.2)	7.8 ± 1.7 (5.7–11.3)
Bulk N (%)	16.7 ± 4.6 (8.2 –29.3)	8.6 ± 5.6 (1.4–18.7)
n-/n-	2.5 ± 2.5 (0.5–9.0)	3.3 ± 1.2 (1.2–4.9)
n-/n-	3.5 ± 1.6 (1.2–6.3)	56.3 ± 14.3 (42.1–89.5)
n-/(n- + n-)	1.1 ± 0.6 (0.4–2.9)	3.1 ± 1.1 (1.2–4.7)
n-/(n- + 2*n-)	0.8 ± 0.4 (0.3–1.7)	2.9 ± 1.0 (1.1–4.5)
NH3 (μg/m^3)	14.1	4.8
NO2 (μg/m^3)	89.2 ± 21.2 (57.0–122.0)	4.3 ± 1.3 (2.6–6.7)
SO2 (μg/m^3)	22.9	0.3
n-NH3/n-NO2	0.4	3.0
n-NH3/n-SO2	2.3	60.2
n-NH3/(n-NO2 + n-SO2)	0.4	2.9
n-NH3/(n-NO2 + 2*n-SO2)	0.3	2.7

Fig. 2. Seventy-two-h air mass backward trajectories for all sampling dates at the Beijing CRAES site and the Menyuan site, based on NOAA HYSPLIT model back trajectories.

Fig. 3. Correlations between δ¹⁵N values of PM_2.5 and molecular ratios of to () (expressed as n-/n-()) in PM_2.5 at Beijing CRAES site and Menyuan site. The regression line was drawn on data of both sites.

Table 3. Fractional contributions (F, %) of dominant N precursors and sources to bulk N in PM_2.5 at Beijing (CRAES site) and a background site (Menyuan, Qinghai province) of China. Values (mean ± SD; n = 10⁴) were calculated based on the output of the SIAR model.

	Beijing (CRAES site)	Menyuan, Qinghai
	40 ± 10	64 ± 11
	41 ± 11	22 ± 10
	1.1 ± 6.3	4.4 ± 5.6
Ffossil	71 ± 12
Fnon-fossil	29 ± 12
Fcoal combustion	39 ± 10
Fvehicle exhausts	32 ± 12
		34 ± 12
Fbiomass burning		46 ± 10

Fig. 4. Fractional contributions of dominant N sources to bulk N in PM_2.5 at the Beijing CRAES site and the Menyuan site. Dots around the boxes (n = 10⁴) show the percentages estimated by the SIAR model. The box encompasses the 25th–75th percentiles, whiskers are the 5th and 95th percentiles. The line and cross in each box mark the median and arithmetic mean values, respectively.

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