Appendix A. Fluorinated Silane Coating Procedure for Pyrex and Quartz

Transcription

1 Appendix A. Fluorinated Silane Coating Procedure for Pyrex and Quartz Coating Compound: United Cemical Tecnologies Compound #T Mix te coating solution: a. Start wit a 200 cm 3 etanol to 10 cm 3 distilled H 2 O solution. b. Bring solution to ph=5 by adding acetic acid dropwise (1 part in 10 5 ). c. Slowly add 2-5% by weigt UTC-T2494. d. Stir 5-15 minutes for ydrolysis. 2. Prepare te Pyrex or quartz surface: a. Was wit a basic lab soap (Micro brand) or treat wit NaOH solution. b. Rinse wit distilled H 2 O. c. Dry torougly. 3. Apply te coating: a. Dip object in solution for 2-5 minutes. For large pieces suc as flow tubes, pour coating solution over te inner surfaces, keeping tem wet for a total of 2-5 minutes. b. Rinse wit etanol. c. Cure minutes at 100 C or overnigt at room temperature and eat briefly wit a eat gun. 143

2 Appendix B. Estimate of te Deposition Velocity of Peroxyacetyl Nitrate (PAN) PAN formation proceeds during te oxidation of biogenic and antropogenic ydrocarbons in te presence of NO x. Te dominant loss mecanism for PAN during te day is termal decomposition to te peroxyacetyl radical and NO 2 [Miller et al., 1999]. PAN may be considered in termo-cemical equilibrium wit peroxyacetyl and NO 2 in te atmospere: CH 3 C(O)O 2 + NO 2 + M CH 3 C(O)O 2 NO 2 + M (RB.1,RB.-1) were Reaction B.1 is te forward reaction, and RB.-1 is te reverse reaction. Removal of te peroxyacetyl radical occurs in te presence of NO [Moise et al., 1999]. CH 3 C(O)O 2 + NO CH 3 C(O)O + NO 2 (RB.2) Te lifetime of PAN is terefore determined by te concentrations of NO and NO 2, and te rates of Reactions (RB.1) and (RB.2) [Moise et al., 1999]: k 1[ 2 ] 1 = 1 + R NO τ 2[ ]. (Eq. B.1) k R NO k R 1 At nigt, observed NO concentrations at Harvard Forest are very low compared to NO 2 due to te lack of potocemical production and low soil emission rate of less tan 0.9 µmol m -2 r -1 at Harvard Forest [Munger et al., 1996]. Using nigttime May, June and July 2000 data from Harvard Forest (wen te PAN instrument was operational), along wit temperature-dependent rate constants k RB.1, k RB.2, and k RB.-1 [DeMore et al., 1997], we calculated te lifetime of PAN against permanent termal decomposition above and below te forest canopy (Table B.1), along wit te lifetime of O 3 against reaction wit NO (Capter 3, Reaction 3.1). 144

3 Table B.1. Median nigttime conditions during May, June, and July 2000; lifetime of PAN; and lifetime of O 3 at Harvard Forest. Above Canopy =28 m Below Canopy =0.5 m T( 0 C) C 15 0 C [NO 2 ]/[NO] τ(pan), (Eq. B.1) 271 Hours 65 Hours τ(o 3 ), (R3.1) 53 Hours 22 Hours Te lifetimes of PAN and O 3 against termal decomposition and cemical loss at nigt are long (Table B.1). Since we observe first-order decay on sorter timescales for particularly stable nigts at Harvard Forest, suc tat C k C t ( t) C 0 e (Eq. B.2) were C is te concentration of O 3 or PAN, it is likely tat deposition is te dominant loss process for bot species under tese conditions. After Sepson et al. [1992], we use observations of PAN and O 3 concentrations, along wit te eddy covariance flux of O 3 above te canopy, to estimate te deposition velocity of PAN. If additional, unidentified cemical loss processes were significant for PAN at nigt, te following estimate would be an upper limit for surface deposition velocity. Also, we make no distinction between loss due to PAN deposition and loss due to peroxyacetyl radical deposition. We write te mass balance for a trace gas species in te nocturnal boundary layer (NBL, eigt = H) as 145

4 H C F FH = dz (Eq. B.3) t were F is te observed eddy covariance flux at eigt =, F H is te flux across te top of te NBL, and C is te concentration of te species. We assume tat gas-pase production and loss are negligible, and tat F H 0. Munger et al. [1996] sowed tat te storage term for O 3, 0 ( C / t) dz, is only significant during te early morning and late afternoon. We consider ere only nigttime data between 20:00 and 04:00, and terefore ignore te storage term. We make te additional assumption tat te concentrations of bot PAN and O3 follow te same simple concentration profile troug te NBL between and H suc tat C(z)=C f(z). Eq. B.3 becomes: dc H ( t) F = f ( z) dz dt (Eq. B.4) Te ratio of te F,PAN to F,O3 becomes (d[pan]/dt)/(d[o 3 ]/dt), and te H integral f ( z) dz cancels. Expressing te flux as te product of deposition velocity and concentration, F=V d C, and combining wit Eq. B.2, we are left wit: k PAN Vd ( PAN) = Vd ( O3 ) (Eq. B.5) k O3 We determine k PAN and k O3 for eac of six nigts were first-order decay was observed by performing te linear regression of ln(c/c 0 ) against time (Figure B.1), and use te mean observed deposition velocity of ozone for te nigt to estimate V d (PAN). Results are summarized in Table B.2. Te resulting mean V d (PAN) was 0.8 ± 0.4 cm s -1. Tis falls witin te range of prior estimates of nigttime PAN deposition velocity over vegetation [Sepson et al., 1992; Scrimpf et al., 1996; McFayden and Cape, 1999]. 146

5 Table B.2. Summary of k [PAN] and k [O3] for six nigts during May, June, and July 2000 wen first order decays of PAN and O 3 were observed. Te product of te ratio of te decay constants wit te deposition velocity of PAN provides an upper limit estimate of te deposition velocity of PAN. Mean ± standard deviation V d (PAN) for te six nigts is 0.8 ± 0.4 cm s -1. Day of Yr k [P AN] (s -1 ) k [O3] (s -1 ) k [PAN]/ k [O3] <V d (O 3 )> ± s.d. (cm s -1 ) V d (PAN) (cm s -1 ) E E ± E E ± E E ± E E ± E E ± E E ± References See Capter

6 Nigt 138 C=[O 3 ] Nigt 139 C=[PAN] ln(c/c 0 ) k O3 =9.30E-6 s -1, R 2 = 0.70 k PAN =5.27E-5 s -1,R 2 = k O3 =1.73E-5 s -1, R 2 = 0.83 k PAN =4.07E-5 s -1,R 2 = 0.78 Nigt 153 Nigt 178 ln(c/c 0 ) k O3 =1.94E-5 s -1, R 2 = 0.96 k PAN =2.06E-5 s -1,R 2 = k O3 =2.58E-5 s -1, R 2 = 0.98 k PAN =5.12E-5 s -1,R 2 = 0.75 ln(c/c 0 ) k O3 =2.12E-5 s -1, R 2 = 0.97 k PAN =1.29E-4 s -1,R 2 = 0.91 Nigt 196 Nigt k O3 =9.54E-6 s -1, R 2 = 0.84 k PAN =3.36E-5 s -1,R 2 = 0.85 Time (s) Time (s) Figure B.1. Linear regressions of ln([o 3 ]/[O 3 ] 0 ) and ln([pan]/[pan] 0 ) vs. time in seconds after 20:00 for six nigts during te summer of 2000 wen concentrations of bot species decayed exponentially overnigt. 148