Supplementary Material
Presence of high nitryl chloride in Asian coastal environment and its impact on atmospheric photochemistry
Yee Jun Tham · Chao Yan · Likun Xue · Qiaozhi Zha · Xinfeng Wang · Tao Wang
Y. J. Tham • C. Yan • L. Xue • Q. Zha • T. Wang (*)
Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong, China.
e-mail:
X. Wang
Environment Research Institute, Shandong University, Ji’nan, Shandong, China.
1 CIMS configuration and ClNO2 measurement
The sample inlet was set at 4 m above ground level. Ambient air was drawn down through a 3-m PFA-Teflon tube (I.D., 9.5 mm; O.D., 12.7 mm) at a total flow of 6 standard liters per minute (SLPM) resulting in residence time in the sampling tube less than 1 second. Immediately before entering CIMS, the last 14.8 cm of inlet was heated with a heater set to 180 ºC and this temperature is unable to dissociate the ClNO2 [1]. Only a small fraction of air (1.55 SLPM) was sampled through an orifice (pin-hole diameter = 0.45 mm) into the ion-molecular reaction (IMR) chamber which was maintained at 11 Torr. Iodide ion (I-) was introduced into the IMR from ionization of a small flow of CH3I (0.03% in N2, Arkonic, USA) diluted in 1.2 SLPM of N2 passing through a 210Po alpha ion source (NRD, P-2031-2000). The ion chemistry for measuring ClNO2 with CIMS has been thoroughly discussed in other studies [2,3]. Briefly, ClNO2 reacted with iodides to generate ion clusters and then moved through an aperture to a lower pressure region (0.5 Torr), collisional dissociation chamber (CDC), to remove the water cluster ion. The ions were transmitted through another octopole and subsequently mass selected by a quadrupole before being detected by a channeltron detector. The final product detected as ClNO2 were ICl- and I(ClNO2)- cluster ions at 162 m/z and 208 m/z, respectively, the latter of which was used in our campaign to quantify the concentrations of ClNO2. The schematic diagram of our TD-CIMS is shown in Fig. S1. ClNO2 was measured with a 6% duty cycle which gives a ∼9 s time resolution for the CIMS data and later used to derive the 1 minute average. The entire ClNO2 signal used in this work was normalized with the primary ion, I- signal counts.
The sensitivity of CIMS towards ClNO2 was determined post field campaign by passing a known concentration of N2O5 through NaCl slurry [4]. The N2O5 was produced by reacting NO2 in excess with O3 [5], and measured as NO3- at 62 m/z. A small flow (150 sccm) of N2O5 was introduced through a Teflon chamber (length = 5 cm; OD = 4.2 cm; volume = 69 cm3) quarter-filled with 4.2 M of NaCl slurry and then diluted into 5 SLPM stream of humidified zero air. The loss of N2O5 concentration after reacting with NaCl was presumed to be 100% converted into ClNO2 as there were over-sufficient of chloride [6]. Our instrument has a response factor of 0.44±0.05 Hz/ppt (mean±SD) for ClNO2 and limit of detection (3σ) was determined to be 2 pptv. Fig. S2 shows the mass spectrum for ClNO2 calibration compared with zero air. To further provide confidence for our measurement of ClNO2, we also measured the ambient isotopic ions of I(37ClNO2)- at 210 m/z. The signal of 210 m/z were well correlated (R2>0.9) with that of 208 m/z and yield a slope of 0.33±0.01 which is about 3 % within the theoretical value of 0.32.
Fig. S1 Schematic diagram of TD-CIMS
Fig. S2 Mass spectrum of ClNO2 calibration and zero air
2 Other instruments
Ozone was measured by a commercial UV photometric analyzer (Model 49i, Thermo Environmental Instruments (TEI), USA). NOx were analyzed with a chemiluminescence instrument (Model 42i, TEI) equipped with a photolytic NO2-converter (Meteorologie Consult Gmbh, Germany). The NO2 photolysis rate (JNO2) was measured using the LI-200 Pyranometer Sensor (LI-COR, USA). The ambient relative humidity (RH) and temperature were monitored with a RH/temperature probe (Model 41382VC/VF, M.R. YOUNG, USA).
3 Comparison with other studies
Table S1 Comparison of our observed maximum ClNO2 mixing ratio with other studies
Location / Maximum observed ClNO2 mixing ratio / ReferenceHouston, Texas, USA / 1.2 ppbv / Osthoff et al. [7]
Los Angeles, California, USA / 2.1 ppbv / Riedel et al. [8]
Boulder, Colorado, USA / 0.45 ppbv / Thornton et al. [9]
Calgary, Canada / 0.25 ppbv / Mielke et al. [2]
Hessen, southwest Germany / 0.8 ppbv / Phillips et al. [10]
HK, China / 1.9 ppbv / This study
4 Air mass types estimated from HYSPLIT model
The air masses during this period can be distinguished into two sections (refer Fig. S3). The first period consists of polluted plumes from Hong Kong urban area and the Pearl River Delta (PRD) region (23rd to 28th August) while the remaining is marine originated, mostly from South China Sea (29th August to 1st September).
Fig. S3 24-hours back trajectories from 23 August to 1 September 2012
References
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