Reactive nitrogen in Asian continental outflow over the western Pacific: Results from the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) airborne mission

Abstract

[1] We present here results for reactive nitrogen species measured aboard the NASA DC-8 aircraft during the Transport and Chemical Evolution over the Pacific (TRACE-P) mission. The large-scale distributions total reactive nitrogen (NO y,sum = NO + NO 2 + HNO 3 + PAN + C 1 -C 5 alkyl nitrates) and O 3 and CO were better defined in the boundary layer with significant degradation of the relationships as altitude increased. Typically, NO y,sum was enhanced over background levels of $260 pptv by 20-to-30-fold. The ratio C 2 H 2 /CO had values of 1-4 at altitudes up to 10 km and as far eastward as 150°E, implying significant vertical mixing of air parcels followed by rapid advection across the Pacific. Analysis air parcels originating from five principal Asian source regions showed that HNO 3 and PAN dominated NO y,sum . Correlations of NO y,sum with C 2 Cl 4 (urban tracer) were not well defined in any of the source regions, and they were only slightly better with CH 3 Cl (biomass tracer). Air parcels over the western Pacific contained a complex mixture of emission sources that are not easily resolvable as shown by analysis of the Shanghai mega-city plume. It contained an intricate mixture of pollution emissions and exhibited the highest mixing ratios of NO y,sum species observed during TRACE-P. Comparison of tropospheric chemistry between the earlier PEM-West B mission and the recent TRACE-P data showed that in the boundary layer significant increases in the mixing ratios of NO y,sum species have occurred, but the middle and upper troposphere seems to have been affected minimally by increasing emissions on the Asian continent over the last 7 years.

On the export of reactive nitrogen from Asia: NO<sub>x</sub> partitioning and effects on ozone

“…3, and discussed below. The observed range in gasphase NO y mixing ratio (200-400 pptv) is broadly consistent with previous observations of NO y in the both the eastern and western Pacific Talbot et al, 2003;Nowak et al, 2004). Further, the vertical distribution of O 3 and NO y are correlated in the troposphere reflecting their coupled source and sink mechanisms.…”

“…This was attributed to a strong gradient in temperature and, hence, PAN thermal dissociation. Talbot et al (2003) showed from observations taken during the TRACE-P experiment that the PAN/NO y ratio exhibited a strong vertical structure, again associated with the temperature dependence in the PAN thermal decomposition rate .…”

“…Previous aircraft observations of NO y over the North Pacific indicate that NO y is primarily comprised of PAN and HNO 3 Talbot et al, 2003;Roberts et al, 2004). These measurements were confined closely to either the Asian or North American continents, with only a select number of transpacific flights that sampled the remote Pacific.…”

The production and persistence of ΣRONO<sub>2</sub> in the Mexico City plume

“…As the plume becomes more dilute, the formation rate will decrease exponentially while the thermal decomposition rate is determined only by the temperature. For urban plumes that experience rapid lofting and wet removal of both HNO 3 and ANs, PNs become the dominant NO y reservoir in the colder, lofted airmass (Altshuller, 1993;Singh and Salas, 1989;Talbot et al, 2003). The Mexico City Plume, as selected based on the criteria described above, was encountered exclusively below 5 km.…”

Exploring Possible Missing Sinks of Nitrate and Its Precursors in Current Air Quality Models —A Case Simulation in the Pearl River Delta, China, Using an Observation-Based Box Model

“…Li et al (2015) simulated summer HNO 3 in Beijing using WRF-Chem and predicted levels in the range 2−5 parts per billion by volume (ppbv), which was much higher than observations (0−1 ppbv). Similar results were also found in the northwestern Pacific, where simulated HNO 3 /NO x and peroxy acetyl nitrate (PAN)/NO x were found to be 2−3 times higher than observations during the Transport and Chemical Evolution over the Pacific (TRACE-P) campaign (Talbot et al 2003). Tang et al (2014) warned that if new additional sources of nitrous acid (HONO) were incorporated into current models, simulated nitrate levels would increase by 80%−100% in China.…”