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We report concentrations of atmospheric NO x , nitric acid (HNO 3 ), peroxyacetyl nitrate (PAN), and NO y ; eddy covariance fluxes of NO x and NO y ; inferred fluxes of HNO 3 at the mixed deciduous Harvard Forest field site, June–November 2000. A novel Tunable Diode Laser Absorption Spectrometer (TDLAS) produced sensitive, hourly HNO 3 concentration data, which were used to evaluate systematic error in the Dry Deposition Inferential Method (DDIM), often employed to estimate weekly HNO 3 flux at deposition monitoring network sites. Due to the weak diurnal variation in HNO 3 concentration at Harvard Forest, no systematic bias was found in the application of this method to compute daily and weekly average fluxes. The sum of individually measured reactive nitrogen species concentrations and fluxes were approximately equal to total NO y concentrations and fluxes for clean Northwesterly flows, but fell short of the total NO y values for the more polluted Southwesterly transport regime. The concentration and deposition velocity of the unmeasured reactive nitrogen compounds were consistent with prior estimates and recent measurements of alkyl- and hydroxyalkyl nitrates, suggesting that these compounds play an important role in reactive nitrogen deposition processes where anthropogenic NO x emissions and natural hydrocarbons are present.

A compact, fast response, infrared spectrometer using four pulsed quantum cascade (QC) lasers has been applied to the analysis of gases in mainstream (MS) and sidestream (SS) cigarette smoke. QC lasers have many advantages over the traditional lead-salt tunable diode lasers, including near room temperature operation with thermoelectric cooling and single mode operation with improved long-term stability. The new instrument uses two 36 m, 0.3 l multiple pass absorption gas cells to obtain a time response of 0.1 s for the MS smoke system and 0.4 s for the SS smoke system. The concentrations of ammonia, ethylene, nitric oxide, and carbon dioxide for three different reference cigarettes were measured simultaneously in MS and SS smoke. A data rate of 20 Hz provides sufficient resolution to determine the concentration profiles during each 2 s puff in the MS smoke. Concentration profiles before, during and after the puffs also have been observed for these smoke constituents in SS smoke. Also, simultaneous measurements of CO 2 from a non-dispersive infrared (NDIR) analyzer are obtained for both MS and SS smoke. In addition, during this work, nitrous oxide was detected in both the MS and SS smoke for all reference cigarettes studied.

Measurement of the isotopic compositions of carbon dioxide and methane is a powerful tool for quantifying their atmospheric sources and sinks, which is especially important considering the dramatic increase in these greenhouse gases during the industrial era. Laser absorption spectroscopy is a technique which has demonstrated the high sensitivity needed for isotopic measurement. A significant problem in the spectroscopic measurement of isotopic abundances is the large difference in concentrations of the major and minor isotopic constituents. The measurement of two isotopic species using lines of similar strength but very unequal concentrations leads to low precision, with either the minor constituent having too small an absorption depth, or the major constituent having too great an absorption depth. If lines with unequal strength are chosen to compensate for the absorption depth imbalance, then precision tends to suffer due to the greater temperature sensitivity of the weaker line strength. We describe the development of a compact instrument for isotopic analysis CO2 and CH4 using tunable infrared laser absorption spectroscopy which combines novel optical design and signal processing methods to address this problem. The design compensates for the large difference in concentration between major and minor isotopes by measuring them with pathlengths which differ by a factor of 72 within the same multipass cell. We have demonstrated the basic optical design and signal processing by determining delta13C (CO2) isotopic ratios with precision as small as 0.2/1000 using a lead salt diode laser based spectroscopic instrument.