Peroxyacetyl nitrate and peroxypropionyl nitrate during SCOS 97-NARSTO.

Peroxyacyl nitrates [RC(O)OONO2] play an important role in urban air quality and tropospheric chemistry. They also receive attention as mutagens, phytotoxins, and possible air quality indicators of changes in vehicle fuel composition. Ambient concentrations of PAN (R = CH3) and PPN (R = C2H5) have been measured during summer 1997 at two southern California locations, Azusa (July 14-October 16) and Simi Valley (June 18-October 16). The highest concentrations were 4.8 ppb for PAN and 0.72 ppb for PPN in Azusa and 3.0 ppb for PAN and 0.28 ppb for PPN in Simi Valley. Ambient levels of PAN and PPN during summer 1997 were lower than those measured in the last three studies carried out in southern California in the summers of 1990, 1991, and 1993. Average PPN/PAN concentration ratios were about the same in Azusa (0.142+/-0.025, n = 132) and in Simi Valley (0.135+/-0.028, n = 138). The PPN/PAN ratio measured in Azusa was the same as that measured at that location in 1993 prior to the introduction in 1996 of California Phase 2 reformulated gasoline. Diurnal variations of PAN and PPN generally followed those of ozone with respect to time of day but not with respect to amplitude. The PAN/ozone ratio was lower in Simi Valley than in Azusa, and daytime minima were recorded at both locations. The amount of PAN lost by thermal decomposition accounted for large fractions of the amount of PAN formed (measured + decomposed) during daytime hours at both locations. The amount of PAN lost by thermal decomposition was higher in Azusa and was up to ca. 8.5 ppb, i.e., 4-5 times more than that measured, when afternoon temperatures were ca. 40 degrees C.

On-road measurement of carbonyls in California light-duty vehicle emissions.

Emissions of carbonyls by motor vehicles are of concern because these species can be hazardous to human health and highly reactive in the atmosphere. The objective of this research was to measure carbonyl emission factors for California light-duty motor vehicles. Measurements were made at the entrance and exit of a San Francisco Bay area highway tunnel, in the center bore where heavy-duty trucks are not allowed. During summer 1999, approximately 100 carbonyls were identified, including saturated aliphatic aldehydes and ketones, unsaturated aliphatic carbonyls, aliphatic dicarbonyls, and aromatic carbonyls. Concentrations were measured for 32 carbonyls and were combined with NMOC, CO, and CO2 concentrations to calculate by carbon balance emission factors per unit of fuel burned. The measured carbonyl mass emitted from light-duty vehicles was 68 +/- 4 mg L(-1). Formaldehyde accounted for 45% of the measured mass emissions, acetaldehyde 12%, tolualdehydes 10%, benzaldehyde 7.2%, and acetone 5.9%. The ozone forming potential of the carbonyl emissions was dominated by formaldehyde (70%) and acetaldehyde (14%). Between 1994 and 1999, emission factors measured at the same tunnel for formaldehyde, acetaldehyde, and benzaldehyde decreased by 45-70%. Carbonyls constituted 3.9% of total NMOC mass emissions and 5.2% of NMOC reactivity. A comparison of carbonyl emissions with gasoline composition supports previous findings that aromatic aldehyde emissions are related to aromatics in gasoline. Carbonyl concentrations in liquid gasoline were also measured. Acetone and MEK were the most abundant carbonyls in unburned gasoline; eight other carbonyls were detected and quantified.

On-road emissions of carbonyls from light-duty and heavy-duty vehicles.

Vehicle emissions are a major source of carbonyls, which play an important role in atmospheric chemistry and urban air quality. Yet, little data are available for speciated carbonyls emitted by vehicles and especially by heavy-duty diesel vehicles. On-road vehicle emissions of carbonyls have been measured in May 1999 at the Tuscarora Mountain Tunnel, PA. Ten saturated aliphatic aldehydes, 4 saturated aliphatic ketones, 4 unsaturated aliphatic carbonyls, 4 aliphatic dicarbonyls, and 9 aromatic carbonyls have been identified and their concentrations measured. For light-duty (LD) vehicles, total carbonyl emissions were ca. 6.4 mg/km, and the 10 largest emission factors were, in decreasing order, those of formaldehyde (2.58 +/- 1.05 mg/km, ca. 40% of total carbonyls), acetone, acetaldehyde, heptanal, crotonaldehyde, 2-butanone, propanal, acrolein, methacrolein, and benzaldehyde. For weight class 7-8 heavy-duty diesel vehicles (7-8 HD), total carbonyl emissions were ca. 26.1 mg/km, and the 10 largest emission factors were, in decreasing order, those of formaldehyde (6.73 +/- 2.05 mg/km, ca. 26% of total carbonyls), acetaldehyde, acetone, crotonaldehyde, m-tolualdehyde, 2-pentanone, benzaldehyde, a C5 saturated aliphatic aldehyde isomer, 2,5-dimethylbenzaldehyde, and 2-butanone. Aromatic carbonyls, unsaturated aliphatic aldehydes, and aliphatic dicarbonyls represented larger fractions of the total carbonyl emissions for 7-8 HD vehicles than for LD vehicles. For HD vehicles, formaldehyde and acetaldehyde emission factors measured in this study are ca. 4-5 times lower than those measured in previous work. For LD vehicles, emission factors measured in this study are generally lower than those measured in earlier work and are about the same, within reported uncertainties, as those measured in 1992 in the same highway tunnel.

Liquid Chromatography Analysis of Carbonyl (2,4-Dinitrophenyl)hydrazones with Detection by Diode Array Ultraviolet Spectroscopy and by Atmospheric Pressure Negative Chemical Ionization Mass Spectrometry.

The (2,4-dinitrophenyl)hydrazones of carbonyls are separated by liquid chromatography and detected by ultraviolet spectroscopy (diode array detector) and by atmospheric pressure negative chemical ionization mass spectrometry. Results are presented for 78 carbonyls including 18 1-alkanals (from formaldehyde to octadecanal), 16 other saturated aliphatic carbonyls (5 C(4)-C(7) aldehydes and 11 C(3)-C(9) ketones), 16 unsaturated aliphatic carbonyls (9 C(3)-C(11) aldehydes and 7 C(4)-C(9) ketones), 13 aromatic carbonyls (including hydroxy- and/or methoxy-substituted compounds), 10 C(2)-C(10) aliphatic dicarbonyls, 3 aliphatic carbonyl esters, and 2 other carbonyls. Isomers were observed for α,ß-unsaturated ketones and saturated carbonyls that bear other oxygen-containing substituents, e.g. methoxyacetone, 2-furaldehyde, and the 3 carbonyl esters. For all but two of the carbonyls studied, the base peak in the negative APCI mass spectrum was the M - 1 ion (NO(2))(2)C(6)H(3)NN [Formula: see text] CR(1)R(2) (R(1) = H for aldehydes), where M is the molecular mass of the carbonyl (2,4-dinitrophenyl)hydrazone derivative. The dicarbonyls 2,4-pentanedione and succinic dialdehyde reacted with DNPH to yield predominantly other products. Concentrations measured by ultraviolet spectroscopy (peak area) and by mass spectrometry (abundance of M - 1 ion) were in good agreement. Applications described include the measurement of 34 C(1)-C(18) carbonyls at levels of 0.015-14 parts per billion (ppb) in urban air and the identification of carbonyls at ppb concentrations as reaction products in laboratory studies of the atmospheric oxidation of unsaturated organic compounds.

Monitoring ambient ozone with a network of passive samplers: a feasibility study.

Ambient levels of ozone have been measured at 46 mountain forest, desert, Class I Wilderness areas and other remote locations using a network of passive samplers. Typical values were 40-80 ppb (2 week samples) and exhibited temporal variations (studied for up to 1 year) as well as changes with elevation (studied up to 10 500 ft (3 200 m)). The performance of the passive sampler was evaluated with respect to reproducibility, field controls, data capture (>0.95), precision for co-located samples (av. = 11.9%, n = 103), and the role of other atmospheric oxidants as potential interferents (2 locations). Suggestions for additional sampler performance evaluation and network operation are outlined.