Aqueous-phase reactions occurred in the PM_2.5 cumulative explosive growth during the heavy pollution episode (HPE) in 2016 Beijing wintertime

Figures & data

Fig. 1. Time series of the PM_2.5 mass concentration in Beijing on 15–23 December 2016. The green, red, and blue lines correspond to the PM_2.5 data in the pollution transport stage (TS), pollution cumulative stage (CS) and clean stage (Clean), respectively. The dashed line corresponds to the daily mean PM_2.5 mass concentration (calculated from 8:00 am to 7:00 am in the following day). The data in the gray boxes were selected to represent the explosive growth (REG) processes.

Table 1. Average mass concentration (µg m⁻³) of PM_2.5, major water-soluble ions, and trace gases during the pollution transport stage (TS), pollution cumulative stage (CS), and clean stage (Clean).

	Clean	TS	CS	TS/Clean	CS/Clean	CS/TS
PM2.5	19.1	206.1	392.5	10.8	20.5	1.9
NO3^–	2.7	21.6	37.3	7.8	13.6	1.7
SO4^2–	2.9	14.4	31.49	4.9	10.7	2.2
NH4^+	0.4	11.5	24.7	28.7	61.7	2.1
Cl^–	0.5	3.9	5.1	7.1	9.3	1.3
K^+	0.2	1.1	1.9	6.4	10.8	1.7
Na^+	3.3	3.8	3.8	1.2	1.2	1
Ca^2+	1.6	1.5	1.5	0.9	0.9	1.0
Mg^2+	0.08	0.11	0.16	1.25	1.9	1.5
NO2	30.03	111.6	155.3	3.7	5.2	1.4
SO2	5.1	34.0	13.31	6.7	2.6	0.4
O3	37.9	3.0	4	0.08	0.1	1.3
HONO	1.52	5.06	12.66	3.32	8.3	2.5

Table 2. Duration and increase rate of the PM_2.5 mass concentration in REG1, REG2, and REG3.

	Start PM2,5 (µg.m^–3)	Final PM2,5 (µg.m^–3)	Time (hour)	Rate (µg.m^–3.h^–1)	R^2
REG1	34	320	12	29.3	0.92
REG2	88	384	14	23.4	0.95
REG3	202	524	12	32.5	0.91

Note: R² values refer to linear correlation coefficient during linear fitting of PM_2.5 mass concentration increase rate.

Fig. 2. Mass fractions of water-soluble inorganic ions in PM_2.5 during HPE on 15–22 December 2016 in Beijing.

Fig. 3. Temporal variations of major water-soluble inorganic ions in PM_2.5.

Fig. 4. Correlation between PM2.5 and (a) Cl^–, (b) K⁺ during the HPE on 15–22 December 2016 in Beijing.

Fig. 5. Temporal variations of the mass concentrations of gaseous SO₂, O₃, NO₂, and HONO during the observation period.

Fig. 6. Time series for the (a) PM_2.5 mass concentration and ambient RH, (b) nitrate and nitrogen dioxide, (c) sulfate, sulfur dioxide, and HONO in REG3.

Fig. 7. Scatter plots of particulate [NH₄⁺] against 2 × [SO₄^2–], 2 × [SO₄^2–] + [NO₃^–], 2 × [SO₄^2–] + [NO₃^–] + [Cl^–] in REG 3. [] refers to molar concentration.

Table 3. Deliquescence relative humidity for (NH₄)₂SO₄, NH₄NO₃, and NH₄Cl in REG3.

Salt	DRH (298.1 K)^a	$-\frac{18m_{\mathrm{s}}{L}_{\mathrm{S}}}{1000R}$^a	DRH in REG3 (271.9 K)^b
(NH4)2SO4	0.7997	80.0	0.82
NH4NO3	0.6183	852.0	0.81
NH4Cl	0.7710	239.0	0.83

^aThe values were originated from reference (Fountoukis and Nenes, 2007).

^bThe temperature here is the mean temperature in the REG 3.

Fig. 8. The relationship between the NOR and the RH in the REG3.

Fig. 9. Relationship between RH and (a) SOR, (b) PM_2.5, and (c) HONO in REG 3.

Fig. 10. Equivalent ratio of (a) ammonium (NH₄⁺) to the sum of SO₄²⁻ and NO₃^–, (b) NH₄⁺ to the sum of SO₄²⁻, NO₃⁻, and Cl⁻, (c) total cations to anions in PM_2.5. The top and bottom of the vertical line for each box correspond to the 95th and 5th percentiles, respectively. While the top, middle, and bottom horizontal lines of the box mark the 75th, 50th, and 25th percentiles of the data range. The white dot in each box represents the mean value.

Fountoukis, C. and Nenes, A. 2007. ISORROPIA II: A computationally efficient thermodynamic equilibrium model for K+-Ca2+-Mg2+-Nh(4)(+)-Na+-SO42–NO3–Cl–H2O aerosols. Atmos. Chem. Phys. 7, 4639–4659. doi:10.5194/acp-7-4639-2007

 Web of Science ®Google Scholar