The relationship between O3 and NOx (NO + NO2) which was measured during summer and winter periods at Niwot Ridge, Colorado, has been analyzed and compared to model calculations. Both model calculations and observations show that the daily O3 production per unit of NOx is greater for lower NOx. Model calculations without nonmethane hydrocarbons (NMHC) tend to underestimate the O3 production rate at NOx higher than 1.5 parts per billion by volume and show the opposite dependence on NOx. The model calculations with NMHC are consistent with the observed data in this regime and demonstrate the importance of NMHC chemistry in the O3 production. In addition, at eight other rural stations with concurrent O3 and NOx measurements in the central and eastern United States the daily O3 increase in summer also agrees with the O3 and NOx relationship predicted by the model. The consistency of the observed and model‐calculated daily summer O3 increase implies that the average O3 production in rural areas can be predicted if NOx is known. The dependence of O3 production rate on NOx deduced in this study provides the basis for a crude estimate of the total O3 production. For the United States an average summer column O3 production of about 1×1012Cm−2S−1 from anthropogenically emitted NOx and NMHC is estimated. This photochemical production is roughly 20 times the average cross‐tropopause O3 flux. Production of O3 from NOx that is emitted from natural sources in the United States is estimated to range from 1.9×1011 to 12×1011 cm−2 s−1, which is somewhat smaller than ozone production from anthropogenic NOx sources. Extrapolation to the entire northern hemisphere shows that in the summer, 3 times as much O3 is generated from natural precursors as those of anthropogenic origin. The winter daily O3 production rate was found to be about 10% of the summer value at the same NOx level. However, because of longer NOx lifetime in the winter, the integrated O3 production over the lifetime of NOx may be comparable to the summer value. Moreover, because the natural NOx sources are substantially smaller in the winter, the wintertime O3 budget in the northern hemisphere should be dominated by ozone production from anthropogenic ozone precursors. The photochemical lifetime of O3 in the winter in the mid‐latitude is approximately 200 days. We propose that this long lifetime allows anthropogenically produced O3 to accumulate and contribute substantially to the observed spring maximum that is usually attributed to stratospheric intrusion. Furthermore, the anthropogenic O3 may be transported not only zonally but also to lower latitudes. Thus the long‐term interannual increase in O3, observed in the winter and spring seasons at Mauna Loa, may be due to the same anthropogenic influences as the similar winter trend observed at Hohenpeissenberg, Germany.

Measurement of the levels of ozone and carbon monoxide (a tracer of anthropogenic pollution) at three surface sites on the Atlantic coast of Canada allow the estimation of the amount of ozone photochemically produced from anthropogenic precursors over North America and transported to the lower troposphere over the temperate North Atlantic Ocean. This amount is greater than that injected from the stratosphere, the primary natural source of ozone. This conclusion supports the contention that ozone derived from anthropogenic pollution has a hemisphere-wide effect at northern temperate latitudes.

[1] Nonmethane hydrocarbons (NMHCs) and oxy hydrocarbons (oxy HCs) were measured aboard the National Oceanic and Atmospheric Administration research vessel Ronald H. Brown during the New England Air Quality Study from 13 July to 10 August 2002 by an online dual gas chromatographic instrument with two separate analytical columns equipped, respectively, with flame ionization and mass spectrometer detectors. Measurements, taken each half hour, included C2 to C10 alkanes, C2 to C5 alkenes, alcohols and ketones, C6 to C9 aromatics, and biogenic volatile compounds including six monoterpenes, isoprene and its immediate oxidation products methacrolein and methylvinylketone. All compounds have been categorized by their contribution to the OH loss rate calculated for 298K and 1 atm. Large temporal variability was observed for all compounds. Airflow from the Providence, Rhode Island/Boston, Massachusetts, urban corridor northeast to the New Hampshire coast was usually heavily laden with NMHCs and oxy HCs of anthropogenic origin. Comparison of specific compound ratios with automotive tunnel studies suggested that these were predominantly mobile source emissions. When such flow occurred during daylight hours, these urban plumes were accompanied by increases in ozone in the 80 to 120 ppbv range. About equally as often, much less chemically mature NMHC plumes were encountered near the New Hampshire coast. Ozone was titrated out of these latter plumes, and the unusually high mixing ratios of C4 and C5 alkenes suggested that their source was partly gasoline vapor release rather than mobile source emissions. In the New England coastal region explored, in spite of the large anthropogenic NMHC input during periods of offshore flow, OH loss with hydrocarbons was frequently dominated by compounds of biogenic origin. During periods of cleaner marine air inflow the OH loss rate was dominated by reaction with methane and with oxy HCs, predominantly acetone, formaldehyde, and acetaldehyde.

[1] We report measurements of NO x , SO 2 , CO, and HCHO mass-based emission factors from more than 200 commercial vessel encounters in the Gulf of Mexico and the Houston-Galveston region of Texas during August and September, 2006. For underway ships, bulk freight carriers have the highest average NO x emissions at $87 g NO x (kg fuel)À1 , followed by tanker ships at $79 g NO x (kg fuel) À1 , while container carriers, passenger ships, and tugs all emit an average of about $60 g NO x (kg fuel)À1 . Emission of NO x from stationary vessels was lower, except for container ships and tugs, and likely reflects use of medium-speed diesel engines. Overall, our mean NO x emission factors are 10-15% lower than published data. Average emission of SO 2 was lower for passenger ships and tugs and tows (6-7 g SO 2 (kg fuel) À1 ) than for larger cargo vessels (20-30 g SO 2 (kg fuel) À1 ). Our data for large cargo ships in this region indicate an average residual fuel sulfur content of $1.4% which is a factor of two lower than the global average of 2.7%. Emission of CO was low for all categories (7-16 g CO (kg fuel) À1 ), although our mean overall CO emission factor is about 10% higher than published data. Emission of HCHO was less than 5% that of CO. Despite considerable variability, no functional relationships, such as emissions changes with engine speed or load, could be discerned. Comparison of emission factors from ships to those from other sources suggests ship emissions in this region cannot be ignored.