Abstract. The nocturnal nitrogen oxides, which include the nitrate radical (NO3),
dinitrogen pentoxide (N2O5), and its uptake product on chloride
containing aerosol, nitryl chloride (ClNO2), can have profound impacts
on the lifetime of NOx (= NO + NO2), radical budgets, and
next-day photochemical ozone (O3) production, yet their abundances and
chemistry are only sparsely constrained by ambient air measurements. Here, we present a measurement data set collected at a routine monitoring
site near the Abbotsford International Airport (YXX) located approximately
30 km from the Pacific Ocean in the Lower Fraser Valley (LFV) on the west
coast of British Columbia. Measurements were made from 20 July to 4 August
2012 and included mixing ratios of ClNO2, N2O5, NO,
NO2, total odd nitrogen (NOy), O3, photolysis frequencies,
and size distribution and composition of non-refractory submicron aerosol
(PM1). At night, O3 was rapidly and often completely removed by dry deposition
and by titration with NO of anthropogenic origin and unsaturated biogenic
hydrocarbons in a shallow nocturnal inversion surface layer. The low
nocturnal O3 mixing ratios and presence of strong chemical sinks for
NO3 limited the extent of nocturnal nitrogen oxide chemistry at ground
level. Consequently, mixing ratios of N2O5 and ClNO2 were low
(< 30 and < 100 parts-per-trillion by volume (pptv) and
median nocturnal peak values of 7.8 and 7.9 pptv, respectively). Mixing
ratios of ClNO2 frequently peaked 1–2 h after sunrise
rationalized by more efficient formation of ClNO2 in the nocturnal
residual layer aloft than at the surface and the breakup of the nocturnal
boundary layer structure in the morning. When quantifiable, production of
ClNO2 from N2O5 was efficient and likely occurred
predominantly on unquantified supermicron-sized or refractory sea-salt-derived aerosol. After sunrise, production of Cl radicals from photolysis of
ClNO2 was negligible compared to production of OH from the reaction of
O(1D) + H2O except for a short period after sunrise.
Routine monitoring stations on the west coast of North America serve to monitor baseline levels of criteria pollutants such as ozone (O3) arriving from the Pacific Ocean. In Canada, the Amphitrite Point Observatory (APO) on Vancouver Island has been added to this network to provide regional baseline measurements. In 2014, McKendry and co-workers reported frequent nocturnal O3 depletion events (ODEs) at APO that generally correlated with alongshore winds, elevated concentrations of carbon dioxide (CO2) and stable boundary layer conditions, but whose cause (or causes) has (have) remained unclear.This manuscript presents results from the Ozone-depleting Reactions in a Coastal Atmosphere (ORCA) campaign, which took place in July, 2015 to further investigate ODEs at APO. In addition to the long-term measurements at the site (e.g., of CO2 and O3 mixing ratios), abundances of biogenic volatile organic compounds (BVOC) and aerosol size distributions were quantified. ODEs were observed on the majority of measurement nights and were characterized by a simultaneous increase of CO2 and BVOC abundances, in particular of limonene, a terpene 2.5 more reactive with respect to oxidation of O3 than other monoterpenes.Back trajectory calculations showed that ODEs occurred mainly in air masses that originated from the WNW where the air would have travelled parallel to the coastline and above kelp forests. Head space analyses of sea weed samples showed that bull kelp is a source of gas-phase limonene, consistent with its high relative abundance in air masses from the WNW sector. However, the enhanced terpene and CO2 content showed that the air likely also came in contact with terrestrial vegetation via mesoscale transport phenomena (such as slope flows and land-sea breeze circulations) that were generally poorly captured by the back trajectories. This absence of aerosol growth during ODEs indicates that dry deposition is likely the primary O3 loss mechanism.
Landfalling atmospheric rivers (ARs) frequently trigger heavy and sometimes prolonged precipitation, especially in regions with favored orographic enhancement. The presence and strength of ARs are often described using the integrated water vapor (IWV) and the integrated vapor transport (IVT). However, the associated precipitation is not directly correlated with these two variables. Instead, the intensity of precipitation is mainly determined by the net convergence of moisture flux and the initial degree of saturation of the air column. In this study, a simple algorithm is proposed for estimating the heavy precipitation attributable to the IVT convergence. Bearing a strong resemblance to the Kuo‐Anthes parameterization scheme for cumulus convection, the proposed algorithm calculates the large‐scale primary condensation rate (PCR) as a proportion of the IVT convergence, with a reduction to account for the general moistening in the atmosphere. The amount of reduction is determined by the column relative humidity (CRH), which is defined as the ratio of IWV to its saturation counterpart. Our analysis indicates that the diagnosable PCR compares well to the forecast precipitation rate given by a numerical weather prediction model. It is also shown that the PCR in an air column with CRH < 0.50 is negligibly small. The usefulness of CRH and PCR as two complements to standard AR analysis is illustrated in three case studies. The potential application of PCR to storm classification is also explored.
At Amphitrite Point, ozone (O 3) mixing ratios are observed to drop steadily to 5-15 ppb over a period of 12 hours or less with a frequency approaching one event per week (with highest frequencies occurring in summer and fall). Analysis of 47 such O 3 depletion events reveals that low O 3 episodes are a predominantly nocturnal phenomenon associated with anticyclonic conditions characterized by light onshore or alongshore winds and an absence of fog and mist. Back-trajectories show air carried to the Amphitrite Point Observatory (APO) during depletion events remains in the marine boundary layer and is not brought to the surface from aloft. There is no strong correlation with other "criteria" pollutants (CO, NO x , SO 2 , PM 2.5) that might be indicative of a mechanism for O 3 destruction linked to human, terrestrial, or marine pollutant sources. However, CO 2 mixing ratios are observed to increase, coincident with O 3 depletion. Together, these results point to a natural marine boundary layer phenomenon in which O 3 destruction dominates O 3 production and/or replenishment by vertical mixing. While there are several candidate mechanisms, the conditions for O 3 depletion (and CO 2 buildup) to occur are set by meteorology and, in particular, development of a stable marine boundary layer in which vertical mixing is suppressed. Support for this interpretation is provided by simultaneous increases in CO 2 in the stable marine boundary that are indicative of an important role played by marine biogenic processes (respiration). Future research should be directed at elucidating the chemical mechanisms responsible for O 3 destruction in the coastal zone, which means that there would be a need for a much broader range of measurements at APO (including halogenated species) as well as offshore measurements of both chemical and marine boundary layer meteorological variables.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.