Case study of deep STE event of ozone at a low latitude Indian station using simultaneous balloon borne ozonesonde and surface ozone measurements

{kksHkeaMy esa vkst+ksu dh ek=k dks izHkkfor djus okys egRoiw.kZ dkjd vkst+ksu dk lerkieaMy {kksHkeaMy esa ijLij fofue; ¼STE½ dk gksuk gSA ;g loZekU; ckr gS fd fuEu v{kka’kksa ij lerkieaMy {kksHkeaMy fofue; ¼STE½ vis{kkd`r vlkekU; gksrk gSA blfy, bl 'kks/k i= esa vkstksu lkSans] mixzg ,oa ijkcSaxuh izdk’kfed vkst+ksu fo’ys"kd vkadM+ksa dk mi;ksx djrs gq, Hkkjr ds fuEu v{kka’k ij fLFkr Å".k dfVca/kh; vkst+ksu ds lerkieaMy {kksHkeaMy fofue; ¼STE½ dh ?kVuk dk xgjkbZ ls v/;;u fd;k x;k gSA Stratosphere Troposphere Exchange (STE) of ozone is an important factor influencing the budget of ozone in the troposphere. It is well established that STE is relatively uncommon at low latitudes. Therefore a case study of deep STE event of ozone at a low latitude tropical coastal site of India is presented in the paper using ozonesonde, satellite and UV photometric ozone analyzer data.

Measurement report: Photochemical production and loss rates of formaldehyde and ozone across Europe

Various atmospheric sources and sinks regulate the abundance of tropospheric formaldehyde (HCHO), which is an important trace gas impacting the HOx (≡ HO2 + OH) budget and the concentration of ozone (O3). In this study, we present the formation and destruction terms of ambient HCHO and O3 calculated from in situ observations of various atmospheric trace gases measured at three different sites across Europe during summertime. These include a coastal site in Cyprus, in the scope of the Cyprus Photochemistry Experiment (CYPHEX) in 2014, a mountain site in southern Germany, as part of the Hohenpeißenberg Photochemistry Experiment (HOPE) in 2012, and a forested site in Finland, where measurements were performed during the Hyytiälä United Measurements of Photochemistry and Particles (HUMPPA) campaign in 2010. We show that, at all three sites, formaldehyde production from the OH oxidation of methane (CH4), acetaldehyde (CH3CHO), isoprene (C5H8) and methanol (CH3OH) can almost completely balance the observed loss via photolysis, OH oxidation and dry deposition. Ozone chemistry is clearly controlled by nitrogen oxides (NOx ≡ NO + NO2) that include O3 production from NO2 photolysis and O3 loss via the reaction with NO. Finally, we use the HCHO budget calculations to determine whether net ozone production is limited by the availability of VOCs (volatile organic compounds; VOC-limited regime) or NOx (NOx-limited regime). At the mountain site in Germany, O3 production is VOC limited, whereas it is NOx limited at the coastal site in Cyprus. The forested site in Finland is in the transition regime.

Seasonality of Coastal Picophytoplankton Growth, Nutrient Limitation, and Biomass Contribution

Picophytoplankton in the Baltic Sea includes the simplest unicellular cyanoprokaryotes (Synechococcus/Cyanobium) and photosynthetic picoeukaryotes (PPE). Picophytoplankton are thought to be a key component of the phytoplankton community, but their seasonal dynamics and relationships with nutrients and temperature are largely unknown. We monitored pico- and larger phytoplankton at a coastal site in Kalmar Sound (K-Station) weekly during 2018. Among the cyanoprokaryotes, phycoerythrin-rich picocyanobacteria (PE-rich) dominated in spring and summer while phycocyanin-rich picocyanobacteria (PC-rich) dominated during autumn. PE-rich and PC-rich abundances peaked during summer (1.1 × 105 and 2.0 × 105 cells mL–1) while PPE reached highest abundances in spring (1.1 × 105 cells mL–1). PPE was the main contributor to the total phytoplankton biomass (up to 73%). To assess nutrient limitation, bioassays with combinations of nitrogen (NO3 or NH4) and phosphorus additions were performed. PE-rich and PC-rich growth was mainly limited by nitrogen, with a preference for NH4 at >15°C. The three groups had distinct seasonal dynamics and different temperature ranges: 10°C and 17–19°C for PE-rich, 13–16°C for PC-rich and 11–15°C for PPE. We conclude that picophytoplankton contribute significantly to the carbon cycle in the coastal Baltic Sea and underscore the importance of investigating populations to assess the consequences of the combination of high temperature and NH4 in a future climate.

Seasonal Analysis of Reduced and Oxidized Nitrogen-Containing Organic Compounds at a Coastal Site

Nitrogen-containing organic compounds, which may be directly emitted to the atmosphere or may form via reactions with prevalent reactive nitrogen species (e.g. NH3, NOx, NO3), have important but uncertain effects on climate and human health. Using gas and liquid chromatography with soft ionization and high-resolution mass spectrometry, we performed a molecular-level speciation of functionalized organic compounds at a coastal site on the Long Island Sound in summer (during the LISTOS 2018 campaign) and winter. This region often experiences poor air quality due to the emissions of reactive anthropogenic, biogenic, and marine-derived compounds and their chemical transformation products. Indeed, we observed a range of functionalized compounds containing oxygen, nitrogen, and/or sulfur atoms resulting from a mix of direct emissions and chemical transformations, including photochemical processing in summer and aqueous-phase processing in winter. In both summer and winter, nitrogen-containing organic aerosols dominated the observed distribution of functionalized particle-phase species ionized by our analytical techniques, with 85 % and 68 % of measured compound abundance containing a nitrogen atom, respectively. Nitrogen-containing particles included reduced nitrogen functional groups (e.g. amines, imines, azoles) and common NOz contributors (e.g. organonitrates). The prevalence of reduced nitrogen functional groups observed in the particle-phase, while frequently paired with oxygen-containing groups elsewhere on the molecule, often rivaled that of oxidized nitrogen groups detected by our methods. Supplemental gas-phase measurements, collected on adsorptive samplers and analyzed with a novel liquid chromatography-based method, suggest that gas-phase reduced nitrogen compounds are possible contributing precursors to the observed nitrogen-containing particles. Altogether, this work highlights the prevalence of reduced nitrogen-containing compounds in the less-studied Northeastern U.S., and potentially in other regions with similar anthropogenic, biogenic, and marine source signatures.

Measurement report: Photochemical production and loss rates of formaldehyde and ozone across Europe

Various atmospheric sources and sinks regulate the abundance of tropospheric formaldehyde (HCHO) which is an important trace gas impacting the HOx (≡ HO2 + OH) budget and the concentration of ozone (O3). In this study, we present the formation and destruction terms of ambient HCHO and O3 calculated from in-situ observations of various atmospheric trace gases measured at three different sites across Europe during summer time. These include a coastal site in Cyprus in the scope of the Cyprus Photochemistry Experiment (CYPHEX) in 2014, a mountain site in Southern Germany as part of the Hohenpeißenberg Photochemistry Experiment (HOPE) in 2012 and a forested site in Finland where measurements were performed during the Hyytiälä United Measurements of Photochemistry and Particles (HUMPPA) campaign in 2010. We show that at all three sites formaldehyde production from the OH oxidation of methane (CH4), acetaldehyde (CH3CHO), isoprene (C5H8) and methanol (CH3OH) can almost completely balance the observed loss via photolysis, OH oxidation and dry deposition. Ozone chemistry is clearly controlled by nitrogen oxides (NOx ≡ NO + NO2) that includes O3 production from NO2 photolysis and O3 loss via the reaction with NO. Finally, we use the HCHO budget calculations to determine whether net ozone production is limited by the availability of VOCs (VOC limited regime) or NOx (NOx limited regime). At the mountain site in Germany O3 production is VOC limited, whereas it is NOx limited at the coastal site in Cyprus. The forested site in Finland is in the transition regime.