Assessment of direct radiative forcing due to secondary organic aerosol over China with a regional climate model

Figures & data

Table 1. Acronyms used in the texts

Acronyms	Description
ISOA	Component of secondary organic aerosol formed from photochemical oxidation of primary organic vapours precursors with volatility higher than 10^4 but lower than 10^6 µg m^−3 at 298 K and 1 atm (Robinson et al., 2007)
AORi	Anthropogenic secondary organic aerosol for bin i, and as i increases, the volatility increases
BORi	Biogenic secondary organic aerosol for bin i, and as i increases, the volatility increases
TRF	Radiative forcing at top of atmosphere
SRF	Radiative forcing at surface

Fig. 1 Research domain setting and geographical locations of the sites selected for model evaluation as well as five defined sub-regions of China (green box for West China, yellow box for South China, red box for Middle China, blue box for North China and orange box for Northeast China).

Table 2. The refractive indices of α-pinene SOA under different wavelengths in literature

	α-pinene (limonene) SOA
Wavelength	Ozonolysis^a	Photooxidation	References
405	1.5–1.4	1.5–1.4	(Nakayama et al., 2012)
532
781
532		1.34–1.56 (limonene)	(Kim et al., 2012)
		1.36–1.52 (pinene)
670	1.4–1.5	1.4–1.53	(Kim et al., 2010)
		1.38–1.53
>350	1.44		(Schnaiter et al., 2003)
Visible	1.45		(Wex et al., 2009)
355			(Nakayama et al., 2010)
532
670		1.42±0.02	(Barkey et al., 2007)
450		1.56±0.04
550		1.51±0.03	(Yu et al., 2008)
700		1.46±0.03
532	1.44		(Kim and Paulson, 2013)
355	1.45±0.02		(Ma and Thompson, 2012)

^aThe process through which SOA is generated from VOC precursor.

Table 3. The toluene refractive indices under different wavelengths in literature

	Toluene SOA
Wavelength	Ozonolysis	Photooxidation	References
405 532 781	n: 1.57–1.39		(Nakayama et al., 2013)
532	k: 0.0018–0.0072 (405 nm)
781	both n and k increase to shorter wavelengths
670		1.4–1.6	(Kim et al., 2010)
355			(Nakayama et al., 2010)
532
532	1.55		(Kim and Paulson, 2013)

Table 4. Experiment settings including size distribution parameters, optical properties (at 550 nm) and category of SOA

Name	Particle size distribution^a	ρp	RI	σext	g	ω	α	SOA^b
ABP	Bimodal	1.0	1.53–6.0×10^−3 i	8.1	0.70	0.97	0.25	ASOA
ABPN	Bimodal	1.0	1.53–1.0×10^−7 i	8.2	0.69	1.00	0.25	ASOA
AUL	Unimodal	1.5	1.47–2.0×10^−4 i	2.6	0.69	1.00	0.25	ASOA
AULD	Unimodal	1.5	1.47–2.0×10^−4 i	2.6	0.69	1.00	0	ASOA
BBP	Bimodal	1.0	1.53–6.0×10^−3 i	8.1	0.70	0.97	0.25	BSOA
BBPN	Bimodal	1.0	1.53–1.0×10^−7 i	8.2	0.69	1.00	0.25	BSOA
BUL	Unimodal	1.5	1.45–1.0×10^−7 i	2.5	0.71	1.00	0.25	BSOA
BULD	Unimodal	1.5	1.45–1.0×10^−7 i	2.5	0.71	1.00	0	BSOA
IBP	Bimodal	1.0	1.53–6.0×10^−3 i	8.1	0.70	0.97	0.25	ISOA
IUP	Unimodal	1.5	1.53–6.0×10^−7 i	2.8	0.67	0.95	0.25	ISOA

R_i stands for ‘dry’ modal radius (µm), σ_i represents standard deviation, C_i is particle number concentration, i is particle mode (‘fine’ for the accumulation mode, and ‘crs’ for the coarse mode), ρ_p stands for particle density (g cm⁻³), α is hygroscopic growth parameter, σ_ext is extinction coefficients (m² g⁻¹), g is asymmetry factors, and ω is single scattering albedos.

^aThe bimodal lognormal size distribution corresponds to the size distribution with C _fine/C _crs=4500, R _fine=0.185, R _crs=1.138, σ _fine=1.492, and σ _crs=2.203. The unimodal lognormal size distribution corresponds to the size distribution with R=0.0212, and σ=0.35.

^bThe category of SOA considered in radiative transfer calculation.

Fig. 2 (a) NCEP Reanalysis 840 mb wind (m s⁻¹) and TRMM precipitation (mm hr⁻¹) field averaged over July 2006. (b) RegCM 840 mb wind field (m s⁻¹) and precipitation (mm hr⁻¹) averaged over July 2006.

Fig. 3 (a) Isoprene, (b) α-pinene, and (c) limonene emission (mg m⁻² day⁻¹) averaged over July 2006.

Fig. 4 (a) OC and (b) xylene emission (mg m⁻² day⁻¹) averaged over July 2006.

Table 5. Precursors’ simulated emission statistics over China^a

Precursors	Abbreviation	Emission
Alkane	PAR	0.38
Alkene	OLT	0.10
	OLI	0.14
Aromatic	TOL	0.25
	XYL	0.12
Isoprene	ISO	2.52
Monoterpene	APIN	0.42
	LIMO	0.22

^aUnits are Tg/month. All quantities are summed over the interior of China for July 2006.

Fig. 5 (a) ASOA, (b) BSOA, and (c) ISOA concentration (µg m⁻³) at model surface averaged over July 2006.

Fig. 6 Vertical distribution (µg m⁻³) of ASOA with effective saturation concentrations of (a) 1, (b) 10, (c) 100, (d) 1000 µg m⁻³ at 300 K and BSOA with effective saturation concentrations of (e) 1, (f) 10, (g) 100, (h) 1000 µg m⁻³ at 300 K averaged along longitude over July 2006.

Table 6. Tendencies for tracer transport and chemistry at model surface^a

SOA category	Chemical reactions	Horizontal advection	Vertical advection	Convective transport	Vertical turbulence	Total rainout	Total washout	Sedimentation
AOR1	2585.9	273.0	−306.2	−582.3	−961.4	−16.6	−37.4	−961.4
AOR2	1559.7	−5.9	−69.3	−248.3	−1068.5	−2.4	−4.3	−161.8
AOR3	342.3	−5.6	−14.3	−39.7	−252.9	−0.4	−0.6	−28.5
AOR4	51.8	−0.8	−2.5	−4.8	−39.4	−0.0	−0.0	−4.1
BOR1	4448.9	176.9	−465.0	−901.5	−2080.3	−16.4	−270.9	−881.5
BOR2	3002.1	9.2	−132.9	−498.3	−2043.0	−4.2	−77.7	−255.2
BOR3	1118.9	3.3	−44.5	−134.6	−826.2	−1.1	−31.5	−84.5
BOR4	171.7	0.7	−6.1	−18.2	−130.5	−0.1	−5.2	−12.4

^aUnits are kg kg⁻¹ s⁻¹×10⁻¹⁷. All quantities are averaged over the interior of China for July 2006. The tracer tendencies due to diffusion and boundary conditions are not listed, as they are one or two order smaller than other processes.

Fig. 7 (a) ASOA, (b) BSOA, and (c) ISOA column burden (mg m⁻²) averaged over July 2006.

Fig. 8 (a) Observed OM and simulated OC concentration (µg m⁻³) averaged over July 2006 for 14 sites. (b) AOD averaged over July 2006 for 14 sites. The bars are simulated ASOA and BSOA AOD, and the dots are monthly-averaged MODIS AOD.

Fig. 9 Aerosol optical depth of ASOA and BSOA averaged over July 2006 for experiment (a) ABP, (b) AUL, (c) BBP, and (d) BUL.

Fig. 10 TOA RF (W m⁻²) averaged over six regions (West China, South China, Middle China, North China, Northeast China and the total area of China) in China over July 2006 for eight experiments (ABP, ABPN, AUL, AULD, BBP, BBPN, BUL and BULD).

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