Insight into ozone profile climatology over northeast China from aircraft measurement and numerical simulation

Tropospheric ozone is a major pollutant that can harm human health, animals and plants. With a rapid development in Northeast China, ozone pollution has become an increasingly serious environmental challenge. To study the ozone distribution and the potential sources of ozone precursors in Northeast China, we analyzed vertical ozone profiles from the In-service Aircraft for a Global Observing System (IAGOS) in 2012-2014 and provided the climatological vertical structure of tropospheric ozone over Shenyang. The tropospheric ozone generally presents high in hot months, mainly due to the combined effects of the strong solar radiation and high volatile organic compounds emission in summer. While in cold months, the ozone is low because of weak solar radiation and high nitrogen oxides emission. Besides, a low-ozone center exists within lower troposphere in August, which is mainly caused by the East Asian summer monsoon prevailing in summer. To analyze the sources of ozone, typical ozone pollution episodes were studied and the results revealed the different pathways for the enhancement of ozone pollution in Shenyang: regional transport of anthropogenic emissions from North China Plain (NCP), long-range transport from Siberian biomass burning and local photochemical production. Modeling results show that the largest contribution to the surface ozone in Northeast China is local anthropogenic emissions (exceed 90%); the regional transport of NCP anthropogenic emissions contribute more to the pollutants around 2 km, and account for more than 50% pollutants during highly ozone polluted days; through long-range transport, Siberian biomass burning in the spring also have a nonnegligible effect on the near-ground ozone in Northeast China. Overall, this study provides tropospheric ozone climatology and its source attribution in Northeast China, and highlight the great importance of regional transport of anthropogenic and biomass burning emissions in ozone pollution.

Impact of cabin ozone concentrations on passenger reported symptoms in commercial aircraft

Due to elevated ozone concentrations at high altitudes, the adverse effect of ozone on air quality, human perception and health may be more pronounced in aircraft cabins. The association between ozone and passenger-reported symptoms has not been investigated under real conditions since smoking was banned on aircraft and ozone converters became more common. Indoor environmental parameters were measured at cruising altitude on 83 US domestic and international flights. Passengers completed a questionnaire about symptoms and satisfaction with the indoor air quality. Average ozone concentrations were relatively low (median: 9.5 ppb). On thirteen flights (16%) ozone levels exceeded 60 ppb, while the highest peak level reached 256 ppb for a single flight. The most commonly reported symptoms were dry mouth or lips (26%), dry eyes (22.1%) and nasal stuffiness (18.9%). 46% of passengers reported at least one symptom related to the eyes or mouth. A third of the passengers reported at least one upper respiratory symptom. Using multivariate logistic (individual symptoms) and linear (aggregated continuous symptom variables) regression, ozone was consistently associated with symptoms related to the eyes and certain upper respiratory endpoints. A concentration-response relationship was observed for nasal stuffiness and eye and upper respiratory symptom indicators. Average ozone levels, as opposed to peak concentrations, exhibited slightly weaker associations. Medium and long duration flights were significantly associated with more symptoms compared to short flights. The relationship between ultrafine particles and ozone on flights without meal service was indicative of ozone-initiated chemistry.

Ozone exposures during trans-continental and trans-Pacific flights

Ozone concentrations were passively monitored in passenger cabins of commercial airliners flying domestic, Pacific, and south-east Asian routes. One-hundred and six flight segments were monitored for either the full duration and/or approximately 3 h during the middle portion of the flight for a total of 145 time-integrated measurements. Over all samples the mean (+/-SD) concentration was 80 p.p.b. (30.1). Twenty percent of the measurements exceeded 100 p.p.b., the FAA-recommended level. Eleven percent of the measurements exceeded 120 p.p.b., the US EPA's short-term National Ambient Air Quality Standard for ozone. Ozone concentrations measured on Pacific flights were substantially higher during mid-flight than over the full flight (95 p.p.b. vs. 56 p.p.b). Ozone concentrations on the northern Pacific routes were higher than concentrations for other Pacific flights. Season comparison showed that ozone levels were higher during the winter and spring than for the summer and fall. Our study shows that even in aircraft with catalytic ozone converters, passengers and flight crew may be exposed to elevated ozone levels on domestic and international flights. Given the frequency of ozone excess, it is recommended that (1) ozone converters should be required equipment on all commercial passenger aircraft for mid and high latitude routes (2) improved maintenance procedures should be required for catalytic converters (e.g., more frequent servicing/replacement), and (3) ozone should be routinely monitored on all mid and high latitude flights.

PRACTICAL IMPLICATIONS

The authors have demonstrated elevated ozone concentrations in passenger cabins. They give several practical recommendations to help solve the problem.