Does green mean clean? Volatile organic emissions from regular versus green cleaning products.

Cleaning products emit a range of volatile organic compounds (VOCs), including some which are hazardous or can undergo chemical transformations to generate harmful secondary pollutants. In recent years, "green" cleaners have become increasingly popular, with an implicit assumption that these are better for our health and/or the environment. However, there is no strong evidence to suggest that they are better for indoor air quality compared to regular products. In this study, the VOC composition of 10 regular and 13 green cleaners was examined by headspace analysis. Monoterpenes were the most prevalent VOCs, with average total monoterpene concentrations of 8.6 and 25.0 mg L-1 for regular and green cleaners, respectively. Speciated monoterpene emissions were applied to a detailed chemical model to investigate the indoor air chemistry following a typical cleaning event. Green cleaners generally emitted more monoterpenes than regular cleaners, resulting in larger increases in harmful secondary pollutant concentrations following use, such as formaldehyde (up to 7%) and PAN species (up to 6%). However, emissions of the most reactive monoterpenes (α-terpinene, terpinolene and α-phellandrene), were observed more frequently from regular cleaners, resulting in a disproportionately large impact on the concentrations of radical species and secondary pollutants that were formed after cleaning occurred.

Characterization of two photon excited fragment spectroscopy (TPEFS) for HNO3 detection in gas-phase kinetic experiments.

We have developed and tested two-photon excited fragment spectroscopy (TPEFS) for detecting HNO3 in pulsed laser photolysis kinetic experiments. Dispersed (220-330 nm) and time-dependent emission at (310 ± 5) nm following the 193 nm excitation of HNO3 in N2, air and He was recorded and analysed to characterise the OH(A2Σ) and NO(A2Σ+) electronic excited states involved. The limit of detection for HNO3 using TPEFS was ∼5 × 109 molecule cm-3 (at 60 torr N2 and 180 µs integration time). Detection of HNO3 using the emission at (310 ± 5 nm) was orders of magnitude more sensitive than detection of NO and NO2, especially in the presence of O2 which quenches NO(A2Σ+) more efficiently than OH(A2Σ). While H2O2 (and possibly HO2) could also be detected by 193 nm TPEFS, the relative sensitivity (compared to HNO3) was very low. The viability of real-time TPEFS detection of HNO3 using emission at (310 ± 5) nm was demonstrated by monitoring HNO3 formation in the reaction of OH + NO2 and deriving the rate coefficient, k2. The value of k2 obtained at 293 K and pressures of 50-200 torr is entirely consistent with that obtained by simultaneously measuring the OH decay and is in very good agreement with the most recent literature values.

Reaction of hydroxyl radicals with C4H5N (pyrrole): temperature and pressure dependent rate coefficients.

Absolute (pulsed laser photolysis, 4-639 Torr N(2) or air, 240-357 K) and relative rate methods (50 and 760 Torr air, 296 K) were used to measure rate coefficients k(1) for the title reaction, OH + C(4)H(5)N → products (R1). Although the pressure and temperature dependent rate coefficient is adequately represented by a falloff parametrization, calculations of the potential energy surface indicate a complex reaction system with multiple reaction paths (addition only) in the falloff regime. At 298 K and 760 Torr (1 Torr = 1.33 mbar) the rate coefficient obtained from the parametrization is k(1) = (1.28 ± 0.1) × 10(-10) cm(3) molecule(-1) s(-1), in good agreement with the value of (1.10 ± 0.27) × 10(-10) cm(3) molecule(-1) s(-1) obtained in the relative rate study (relative to C(5)H(8), isoprene) at this temperature and pressure. The accuracy of the absolute rate coefficient determination was enhanced by online optical absorption measurements of the C(4)H(5)N concentration at 184.95 nm using a value σ(184.95nm) = (1.26 ± 0.02) × 10(-17) cm(2) molecule(-1), which was determined in this work.

Removal of the potent greenhouse gas NF3 by reactions with the atmospheric oxidants O(1D), OH and O3.

Nitrogen trifluoride, NF(3), a trace gas of purely anthropogenic origin with a large global warming potential is accumulating in the Earth's atmosphere. Large uncertainties are however associated with its atmospheric removal rate. In this work, experimental and theoretical kinetic tools were used to study the reactions of NF(3) with three of the principal gas-phase atmospheric oxidants: O((1)D), OH and O(3). For reaction (R2) with O((1)D), rate coefficients of k(2)(212-356 K) = (2.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1) were obtained in direct competitive kinetics experiments, and experimental and theoretical evidence was obtained for F-atom product formation. These results indicate that whilst photolysis in the stratosphere remains the principal fate of NF(3), reaction with O((1)D) is significant and was previously underestimated in atmospheric lifetime calculations. Experimental evidence of F-atom production from 248 nm photolysis of NF(3) was also obtained, indicating that quantum yields for NF(3) destruction remain significant throughout the UV. No evidence was found for reaction (R3) of NF(3) with OH indicating that this process makes little or no contribution to NF(3) removal from the atmosphere. An upper-limit of k(3)(298 K) < 4 × 10(-16) cm(3) molecule(-1) s(-1) was obtained experimentally; theoretical analysis suggests that the true rate coefficient is more than ten orders of magnitude smaller. An upper-limit of k(4)(296 K) < 3 × 10(-25) cm(3) molecule(-1) s(-1) was obtained in experiments to investigate O(3) + NF(3) (R4). Altogether these results underpin calculations of a long (several hundred year) lifetime for NF(3). In the course of this work rate coefficients (in units of 10(-11) cm(3) molecule(-1) s(-1)) for removal of O((1)D) by n-C(5)H(12), k(6) = (50 ± 5) and by N(2), k(7) = (3.1 ± 0.2) were obtained. Uncertainties quoted throughout are 2σ precision only.

Rate coefficients for the reaction of iodine oxide with methyl peroxy radicals.

Pulsed laser photolysis radical generation is used to study the title reaction IO+CH(3)O(2)→products. Sensitive and selective laser-induced fluorescence detection of IO allows excess CH(3)O(2) conditions to be maintained throughout, ensuring minimal interference from other fast IO reactions. The rate coefficients, k(5)(296 K)=(3.4±1.4)×10(-12) cm(3) molecule(-1) s(-1), are obtained relative to a well-characterised reference value (k(3) for IO+HO(2)). This result agrees well with a previous determination from this laboratory and demonstrates that the above reaction proceeds an order of magnitude slower than suggested in other recent experimental and theoretical studies. Implications for HOx production/O(3) destruction within the marine boundary layer are briefly discussed.

LIF studies of iodine oxide chemistry. Part 3. Reactions IO + NO3 --> OIO + NO2, I + NO3 --> IO + NO2, and CH2I + O2 --> (products): implications for the chemistry of the marine atmosphere at night.

The technique of pulsed laser photolysis coupled to LIF detection of IO was used to study IO + NO(3) --> OIO + NO(2); I + NO(3) --> (products); CH(2)I + O(2) --> (products); and O((3)P) + CH(2)I(2) --> IO + CH(2)I, at ambient temperature. was observed for the first time in the laboratory and a rate coefficient of k(1 a) = (9 +/- 4) x 10(-12) cm(3) molecule(-1) s(-1) obtained. For , a value of k(2) (298 K) = (1.0 +/- 0.3) x 10(-10) cm(3) molecule(-1) s(-1) was obtained, and a IO product yield close to unity determined. IO was also formed in a close-to-unity yield in , whereas in an upper limit of alpha(3)(IO) < 0.12 was derived. The implications of these results for the nighttime chemistry of the atmosphere were discussed. Box model calculations showed that efficient OIO formation in was necessary to explain field observations of large OIO/IO ratios.

Reaction of HO with glycolaldehyde, HOCH2CHO: rate coefficients (240-362 K) and mechanism.

Absolute rate coefficients for the title reaction, HO+HOCH2CHO-->products (R1), were measured over the temperature range 240-362 K using the technique of pulsed laser photolytic generation of the HO radical coupled to detection by pulsed laser induced fluorescence. Within experimental error, the rate coefficient, k1, is independent of temperature over the range covered and is given by k1(240-362 K)=(8.0+/-0.8)x10(-12) cm3 molecule-1 s-1. The effects of the hydroxy substituent and hydrogen bonding on the rate coefficient are discussed based on theoretical calculations. The present results, which extend the database on the title reaction to a range of temperatures, indicate that R1 is the dominant loss process for HOCH2CHO throughout the troposphere. As part of this work, the absorption cross-section of HOCH2CHO at 184.9 nm was determined to be (3.85+/-0.2)x10(-18) cm2 molecule-1, and the quantum yield of HO formation from the photolysis of HOCH2CHO at 248 nm was found to be (7.0+/-1.5)x10(-2).

Determination of the rate coefficients for the reactions IO + NO2 + M (air) --> IONO2 + M and O(3P) + NO2 --> O2 + NO using laser-induced fluorescence spectroscopy.

Laser-induced fluorescence spectroscopy via excitation of the A2pi(3/2) <-- X2pi(3/2) (2,0) band at 445 nm was used to monitor IO in the presence of NO2 following its generation in the reactions O(3P) + CF3I and O(3P) + I2. Both photolysis of O3 (248 nm) and NO2 (351 nm) were used to initiate the production of IO. The rate coefficients for the thermolecular reaction IO + NO2 + M --> IONO2 + M were measured in air, N2, and O2 over the range P = 18-760 Torr, covering typical tropospheric conditions, and were found to be in the falloff region. No dependence of k1 upon bath gas identity was observed, and in general, the results are in good agreement with recent determinations. Using a Troe broadening factor of F(B) = 0.4, the falloff parameters k0(1) = (9.5 +/- 1.6) x 10(-31) cm6 molecule(-2) s(-1) and k(infinity)(1) = (1.7 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1) were determined at 294 K. The temporal profile of IO at elevated temperatures was used to investigate the thermal stability of the product, IONO2, but no evidence was observed for the regeneration of IO, consistent with recent calculations for the IO-NO2 bond strength being approximately 100 kJ mol(-1). Previous modeling studies of iodine chemistry in the marine boundary layer that utilize values of k1 measured in N2 are hence validated by these results conducted in air. The rate coefficient for the reaction O(3P) + NO2 --> O2 + NO at 294 K and in 100 Torr of air was determined to be k2 = (9.3 +/- 0.9) x 10(-12) cm3 molecule(-1) s(-1), in good agreement with recommended values. All uncertainties are quoted at the 95% confidence limit.

Reaction of HO with hydroxyacetone (HOCH2C(O)CH3): rate coefficients (233-363 K) and mechanism.

Absolute rate coefficients for the title reaction, HO + HOCH(2)C(O)CH(3)--> products (R1) were measured over the temperature range 233-363 K using the technique of pulsed laser photolytic generation of the HO radical coupled to detection by pulsed laser induced fluorescence. The rate coefficient displays a slight negative temperature dependence, which is described by: k(1)(233-363 K) = (2.15 +/- 0.30) x 10(-12) exp{(305 +/- 10)/T} cm(3) molecule(-1) s(-1), with a value of (5.95 +/- 0.50) x 10(-12) cm(3) molecule(-1) s(-1) at room temperature. The effects of the hydroxy-substituent and hydrogen bonding on the rate coefficient are discussed based on theoretical calculations. The present results, which extend the database on the title reaction to a range of temperatures, indicate that R1 is the dominant loss process for hydroxyacetone throughout the troposphere, resulting in formation of methylglyoxal at all atmospheric temperatures. As part of this work, the rate coefficient for reaction of O((3)P) with HOCH(2)C(O)CH(3) (R4) was measured at 358 K: k(4)(358 K) = (6.4 +/- 1.0) x 10(-14) cm(3) molecule(-1) s(-1) and the absorption cross section of HOCH(2)C(O)CH(3) at 184.9 nm was determined to be (5.4 +/- 0.1) x 10(-18) cm(2) molecule(-1).

The reaction of IO with CH3SCH3: products and temperature dependent rate coefficients by laser induced fluorescence.

The technique of pulsed laser photolysis was coupled to laser induced fluorescence detection of iodine oxide (IO) to measure rate coefficients, k(1)(T), for the title reaction IO + CH3SCH3 --> products (R1). A value of k1(298 K) = (1.44 +/- 0.15) x 10(-14) cm3 molecule(-1) s(-1) was obtained, independent of bath gas pressure (50 < P((N2 or air))/Torr < 300). The expression k1(T) = (3.2 +/- 1.4)x 10(-13)exp[(-925 +/- 136)/T)] adequately described the data over the range of temperatures (256 < T/K < 341) covered. Uncertainties (2sigma) in the 298 K rate coefficient and the pre-exponential factor include an estimate of systematic error. The conventional Arrhenius behaviour of k1(T) and the lack of pressure dependence are suggestive of an abstraction mechanism, characterised by an energy barrier of E approximately 8 kJ mol(-1). The product yield for production of I-atoms was determined indirectly to be close to unity, indicating that the reaction proceeds via transfer of the O-atom from IO to CH3SCH3 to form CH3S(O)CH3. In general, the values of k1(T) measured in this work indicate that has little impact on the chemistry of the atmosphere.

Laser induced fluorescence studies of iodine oxide chemistry. Part II. The reactions of IO with CH3O2, CF3O2 and O3.

The technique of pulsed laser photolysis was coupled to laser induced fluorescence detection of iodine oxide (IO) to measure rate coefficients, k for the reactions IO + CH(3)O(2)--> products (R1, 30-318 Torr N(2)), IO + CF(3)O(2)--> products (R2, 70-80 Torr N(2)), and IO + O(3)--> OIO + O(2) (R3a). Values of k(1) = (2 +/- 1) x 10(-12) cm(3) molecule(-1) s(-1), k(2) = (3.6 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1), and k(3a) <5 x 10(-16) cm(3) molecule(-1) s(-1) were obtained at T = 298 K. In the course of this work, the product yield of IO from the reaction of CH(3)O(2) with I was determined to be close to zero, whereas CH(3)OOI was formed efficiently at 70 Torr N(2). Similarly, no evidence was found for IO formation in the CF(3)O(2) + I reaction. An estimate of the rate coefficients k(CH(3)O(2) + I) = 2 x 10(-11) cm(3) molecule(-1) s(-1) and k(CH(3)OOI + I) = 1.5 x 10(-10) cm(3) molecule(-1) s(-1) was also obtained. The results on k(1)-k(3) are compared to the limited number of previous investigations and the implications for the chemistry of the marine boundary layer are briefly discussed.

A laser photolysis-resonance fluorescence study of the reactions: I + O3 --> IO + O2, O + I2 --> IO + I, and I + NO2 + M --> INO2 + M at 298 K.

Laser flash photolysis coupled to resonance-fluorescence detection of I atoms was used to measure the rate coefficients for the reactions: I + O3 --> IO + O2 (R1), O + I2 --> IO + I (R6) and I + NO2 + M --> INO2 + M (R7). All experiments were conducted under pseudo first-order conditions, and the accuracy of the results was enhanced by online determination of reagent concentrations by optical absorption. Bimolecular rate coefficients for reactions (R1) and (R6) were determined to be k1 = (1.28 +/- 0.06) x 10(-12) and k6 = (1.2 +/- 0.1) x 10(-10) cm3 molecule(-1) s(-1) at 298 +/- 2 K, independent of pressure. Rate coefficients for the termolecular reaction (R7), also at 298 +/- 2 K, were found to be in the falloff region between 3rd and 2nd order behaviour and, when combined with other datasets obtained at higher and lower pressures, were adequately described by a simplified Troe function with the parameters: k7,0 (He, 330 K) = 1.48 x 10(-31) cm6 molecule(-2) s(-1), F(C) (He) = 0.43, and k7, infinity = 1.1 x 10(-10) cm3 molecule(-1) s(-1) for He as bath gas. In N2 (or air) the following parameters were obtained k7,0 (N2, 300 K) = 3.2 x 10(-31) cm6 molecule(-2) s(-1), F(C) ( N2) = 0.48, with k7, infinity set to 1.1 x 10(-10) cm3 molecule(-1) s(-1) as obtained from analysis of the falloff curve obtained in He.