Springtime measurements of ozone, nonmethane hydrocarbons, and oxidized nitrogen species at Rishiri, 45°N in east Asian Pacific rim region during risotto 2000: NOy speciation and photochemistry

Measurements of ozone, nonmethane hydrocarbons, and oxdized nitrogen species (NOx, PAN, and HNO3) have been conducted during Rishiri Island Study of Oxidants and Transport for Tropospheric Ozone (RISOTTO) 2000. The campaign was made from winter to summer 2000, at Rishiri island, a northern remote island in Japan. An observatory is located at 45‹ N, near the northern-tip of Japan, and the altitude is 35 m asl. Northern Japan frequently receives continental outflow from Siberia, especially from winter to late spring, hence, air masses observed at the site are Eurasian continental background. NOx, PAN, and HNO3 were measured by chemiluminescence analyzer equipped with photolytic converter (PLC/CL), gas chromatograph/negative ion chemical ionization mass spectrometer (GC/NICI MS), and chemical ionization mass spectrometer utilizing ion-molecule reactions (IMR CIMS), respectively. Individual NMHCs (alkane, alkene, acetylene, isoprene, terpene) were quantified by gas chromatograph/flame ionization detector (GC/FID) after whole air sampling to stainless steel canisters. Ozone showed springtime maximum of ~55 ppbv, similar to other remote sites in the Northern Hemisphere. PAN also showed springtime enhancement of ~500 pptv showing more larger amplitude than that of ozone. In contrast to PAN, HNO3 showed monotonous increase from winter to summer, taking summer maximum of ~1 ppbv. PAN was the most abundant NOy species in winter reflecting PANfs longer lifetime, and larger wet deposition rate of HNO3, while HNO3 was the most abundant in summer reflecting the balance of PANfs shorter lifetime, and larger photochemical production rate (due to increasing OH radicals) and reduced wet removal of HNO3. Spring seems the transition period in terms of the partitioning between PAN and HNO3, but the production of PAN was more dominant than that of HNO3. The behavior of several NMHCs including ethane, propane, propene, acetylene, was primarily explained by the seasonal cycle of OH radicals. The contribution of photochemistry to ozone spring maximum at the site was examined utilizing seasonal variations of NMHCs and individual NOy species. Ozone production efficiency was also derived from NOy species and ozone relationship.