Dataset Information

Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes.

ABSTRACT: Delhi, India, suffers from periods of very poor air quality, but little is known about the chemical production of secondary pollutants in this highly polluted environment. During the postmonsoon period in 2018, extremely high nighttime concentrations of NO_x (NO and NO₂) and volatile organic compounds (VOCs) were observed, with median NO_x mixing ratios of ∼200 ppbV (maximum of ∼700 ppbV). A detailed chemical box model constrained to a comprehensive suite of speciated VOC and NO_x measurements revealed very low nighttime concentrations of oxidants, NO₃, O₃, and OH, driven by high nighttime NO concentrations. This results in an atypical NO₃ diel profile, not previously reported in other highly polluted urban environments, significantly perturbing nighttime radical oxidation chemistry. Low concentrations of oxidants and high nocturnal primary emissions coupled with a shallow boundary layer led to enhanced early morning photo-oxidation chemistry. This results in a temporal shift in peak O₃ concentrations when compared to the premonsoon period (12:00 and 15:00 local time, respectively). This shift will likely have important implications on local air quality, and effective urban air quality management should consider the impacts of nighttime emission sources during the postmonsoon period.

SUBMITTER: Nelson BS

PROVIDER: S-EPMC10275353 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature

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Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes.

Nelson Beth S BS Bryant Daniel J DJ Alam Mohammed S MS Sommariva Roberto R Bloss William J WJ Newland Mike J MJ Drysdale Will S WS Vaughan Adam R AR Acton W Joe F WJF Hewitt C Nicholas CN Crilley Leigh R LR Swift Stefan J SJ Edwards Pete M PM Lewis Alastair C AC Langford Ben B Nemitz Eiko E Shivani Gadi Ranu R Gurjar Bhola R BR Heard Dwayne E DE Whalley Lisa K LK Şahin Ülkü A ÜA Beddows David C S DCS Hopkins James R JR Lee James D JD Rickard Andrew R AR Hamilton Jacqueline F JF

Environmental science & technology letters 20230503 6

Delhi, India, suffers from periods of very poor air quality, but little is known about the chemical production of secondary pollutants in this highly polluted environment. During the postmonsoon period in 2018, extremely high nighttime concentrations of NOx (NO and NO2) and volatile organic compounds (VOCs) were observed, with median NOx mixing ratios of ∼200 ppbV (maximum of ∼700 ppbV). A detailed chemical box model constrained to a comprehensive suite of specia ...[more]

PMID: 37333938

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Project description:This study discusses an analysis of combined airborne and ground observations of particulate nitrate (NO3 - (p)) concentrations made during the wintertime DISCOVER-AQ study at one of the most polluted cities in the United States, Fresno, CA in the San Joaquin Valley (SJV) and focuses on development of understanding of the various processes that impact surface nitrate concentrations during pollution events. The results provide an explicit case-study illustration of how nighttime chemistry can influence daytime surface-level NO3 - (p) concentrations, complementing previous studies in the SJV. The observations exemplify the critical role that nocturnal chemical production of NO3 - (p) aloft in the residual layer (RL) can play in determining daytime surface-level NO3 - (p) concentrations. Further, they indicate that nocturnal production of NO3 - (p) in the RL, along with daytime photochemical production, can contribute substantially to the build-up and sustaining of severe pollution episodes. The exceptionally shallow nocturnal boundary layer heights characteristic of wintertime pollution events in the SJV intensifies the importance of nocturnal production aloft in the residual layer to daytime surface concentrations. The observations also demonstrate that dynamics within the RL can influence the early-morning vertical distribution of NO3 - (p), despite low wintertime wind speeds. This overnight reshaping of the vertical distribution above the city plays an important role in determining the net impact of nocturnal chemical production on local and regional surface-level NO3 - (p) concentrations. Entrainment of clean free tropospheric air into the boundary layer in the afternoon is identified as an important process that reduces surface-level NO3 - (p) and limits build-up during pollution episodes. The influence of dry deposition of HNO3 gas to the surface on daytime particulate nitrate concentrations is important but limited by an excess of ammonia in the region, which leads to only a small fraction of nitrate existing in the gas-phase even during the warmer daytime. However, in late afternoon, when diminishing solar heating leads to a rapid fall in the mixed boundary layer height, the impact of surface deposition is temporarily enhanced and can lead to a substantial decline in surface-level particulate nitrate concentrations; this enhanced deposition is quickly arrested by a decrease in surface temperature, which drops the gas-phase fraction to near zero. The overall importance of enhanced late afternoon gas-phase loss to the multiday build-up of pollution events is limited by the very shallow nocturnal boundary layer. The case study here demonstrates that mixing down of NO3 - (p) from the RL can contribute a majority of the surface-level NO3 - (p) in the morning (here, ~80%), and a strong influence can persist into the afternoon even when photochemical production is maximum. The particular day-to-day contribution of aloft nocturnal NO3 - (p) production to surface concentrations will depend on prevailing chemical and meteorological conditions. Although specific to the SJV, the observations and conceptual framework further developed here provide general insights into the evolution of pollution episodes in wintertime environments.

Project description:IntroductionSodium homeostasis is intimately associated with blood pressure (BP) rhythm, and potassium excretion is closely associated with sodium excretion in the general population. However, the association between circadian sodium and potassium pattern excretion and nocturnal BP in patients with chronic kidney disease (CKD) is not elucidated.MethodsWe evaluated the correlation between the day-to-night ratio of urinary sodium and potassium excretion rate, nocturnal blood pressure, and nocturnal BP dipping in a CKD cohort.ResultsA total of 3152 (56.76% males, mean age 47.63 years) individuals with CKD were included in the study. Patients in quartile 1 (with the lowest ratio) exhibited a 12 mmHg or 9 mmHg higher nocturnal systolic blood pressure (SBP) and blunted SBP dipping than those in quartile 4 when urinary sodium or potassium excretion rate was divided into day-to-night ratios (both P < 0.001). In multivariate analyses, lower day-to-night ratio of urinary sodium was independently linked to higher nocturnal SBP and blunted SBP dipping (linear regression coefficient (95% confidence interval [CI]): -6.89 (-9.48 to -4.31), and -3.64 (-5.48 to -1.80), respectively; both P < 0.001). Similarly, compared with the highest quartile of day-to-night ratio of urinary potassium excretion rate, linear regression coefficient (95% CI) for the lowest quartile was -5.60 (-8.13 to -3.07) for nocturnal SBP, and -2.47 (-4.28 to -0.67) for SBP dipping (both P < 0.001). Moreover, urine flow rate and concentrates of sodium or potassium in the urine were positively associated with urinary sodium or potassium excretion during daytime (P < 0.001).ConclusionA higher nocturnal BP and a blunted nocturnal BP dipping were both independently linked to a lower excretion of sodium or potassium during the day in patients with CKD. Furthermore, a decreased urine flow rate and a diminished capacity to concentrate sodium or potassium in the urine appear to be the key contributors to a low day-to-night ratio of urinary sodium excretion or potassium rate.

Dataset Information

Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes.

Publications

Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes.

Similar Datasets

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