Hydrolysis of Organonitrate Functional Groups in Aerosol Particles

Figures & data

TABLE 1 Experimental conditions including initial mixing ratios of TMB and NO_x, RH, total organic loading (M _org), mass fraction of ON groups (F_ON), yield of OM (Y _OM), molar ratio of alkane and ON groups (R _mole) in SOA, and availability of PSAP measurements.

	Date	TMB0 (ppb)	NOx0 (ppb)	TMB: NOx	RH (%)	M org (μg m^–3)	F ON (%)	Y OM (%)	R mole	PSAP
Experiments	3/12/2011	454.8	1483.7	0.31	<1.5	37.0	19.9	1.7	8.7
addressing RH	3/23/2011	291.8	1799.9	0.17	<0.3	46.7	19.0	3.3	9.2	Yes
effects	3/15/2011	370.1	1639.8	0.24	15.0–20.0	65.7	19.0	3.6	8.5
	3/17/2011	366.8	2264.7	0.17	37.8–49.0	70.6	11.9	3.9	21.2
	3/21/2011	380.6	1610.0	0.24	53.7–66.8	73.4	7.9	3.9	37.5	Yes
	3/28/2011	276.8	1854.8	0.17	85.2–86.5	61.0	4.8	4.5	73.1
Experiments	4/2/2011	337.9	215.1	1.99	<0.4	97.4	10.5	5.9	16.1	Yes
addressing NOx	4/5/2011	310.2	250.0	1.42	37.3–51.0	80.8	8.2	5.3	29.9	Yes
effects	4/7/2011	206.2	30.2	10.78	0	34.9	5.3	3.5	41.7	Yes
	4/4/2011	237.6	30.3	12.45	46.1–60.0	32.9	2.2	2.8	139.7

FIG. 1 (a) Representative FTIR spectra for SOA produced under high-NO_x (23 March) and low-NO_x conditions (2 April). Absorptions near 1100 and 2360 cm⁻¹ (grey areas) are not shown due to interferences by Teflon substrates and CO₂, respectively. (b) Comparison of IR spectra in the 750 to 950 cm⁻¹ region for high-NO_x SOA, ammonium nitrate, and condensed-phase nitric acid. Spectra are normalized in order to show differences. (Color figure available online.)

FIG. 2 (a) Typical mass spectrum for SOA generated under high-NO_x conditions (23 March). (b) Mass fraction of nitrogen-containing fragments (on 23 March). (c) Comparison of FTIR-measured ON groups (ONO₂) and AMS-measured nitrate for all experiments. The RH (%) is indicated by the vertical scale. (Color figure available online.)

FIG. 3 Time-dependence of (a) RH, (b) temperature, (c) TMB, (d) NO, (e) AMS-measured OM, and (f) AMS-measured nitrate. The AMS measurements on 28 March (RH ∼85%) were only available 1 h after the lights were on due to improper experimental setup during the first hour. (Color figure available online.)

FIG. 4 Example (15 March) time-dependence of size distributions of AMS-measured OM and nitrate. (Color figure available online.)

FIG. 5 (a) RH dependence of organic functional group mass fraction for the high-NO_x experiments (12–28 March). The mass fractions are derived from the FTIR measurements. (b) Production rate of AMS-measured OM and nitrate. (Color figure available online.)

FIG. 6 Time-dependence of nitrate-to-OM ratio (measured by the AMS). The lines represent linear fits of the measurements, with slopes of 7.1 × 10⁻⁵, 1.0 × 10⁻⁴, 2.2 × 10⁻⁴, 1.7 × 10⁻⁴, and 2.0 × 10⁻⁴ for RH < 2%, RH = 15–20%, RH = 38–49%, RH = 54–67%, and RH = 85–87% experiments, respectively. (Color figure available online.)

FIG. 7 Structure of molecule A—a likely product of 1,2,4-TMB and OH reaction system.

FIG. 8 Mass absorption coefficient (MAC) (left axis), ON group mass fraction (right axis), and normalized (by OM) nitroaromatic group peak area (scale is not shown) for low-RH (<2%) and intermediate-RH (∼50%) experiments (dates are shown in the parentheses), respectively. The TMB-to-NO_x ratio is indicated by the vertical scale. The ON group mass fraction was determined for the 30 min average around the peak absorption for each experiment using the scaled AMS nitrate mass fraction. The scaling factor was derived by linear regression (slope = 0.60; R = 0.83) of FTIR ON group mass fraction and AMS nitrate mass fraction. (Color figure available online.)